Refine
Has Fulltext
- yes (243)
Is part of the Bibliography
- yes (243)
Year of publication
- 2024 (4)
- 2023 (9)
- 2022 (29)
- 2021 (36)
- 2020 (29)
- 2019 (17)
- 2018 (8)
- 2017 (4)
- 2016 (15)
- 2015 (3)
- 2014 (2)
- 2013 (3)
- 2012 (3)
- 2011 (2)
- 2010 (2)
- 1994 (15)
- 1993 (6)
- 1992 (6)
- 1991 (7)
- 1990 (7)
- 1989 (7)
- 1988 (5)
- 1987 (4)
- 1986 (3)
- 1985 (1)
- 1984 (1)
- 1983 (4)
- 1982 (1)
- 1979 (1)
- 1978 (1)
- 1975 (2)
- 1974 (1)
- 1973 (2)
- 1972 (2)
- 1971 (1)
Document Type
- Journal article (243) (remove)
Language
- English (243) (remove)
Keywords
- Organische Chemie (59)
- fluorescence (10)
- self-assembly (9)
- water oxidation (9)
- Chemie (7)
- RNA (7)
- photocatalysis (7)
- polycyclic aromatic hydrocarbons (7)
- organic chemistry (6)
- SARS-CoV-2 (5)
- dyes (5)
- liquid crystals (5)
- luminescence (5)
- chemistry (4)
- circular dichroism (4)
- dyes/pigments (4)
- in vitro selection (4)
- perylene bisimide (4)
- sphingolipids (4)
- structure elucidation (4)
- supramolecular chemistry (4)
- absolute configuration (3)
- aggregation (3)
- aromaticity (3)
- artificial photosynthesis (3)
- boranes (3)
- catalysis (3)
- cell imaging (3)
- ceramide (3)
- ceramides (3)
- chirality (3)
- energy transfer (3)
- exciton coupling (3)
- homogeneous catalysis (3)
- kinetics (3)
- macrocycles (3)
- molecular docking (3)
- organic photodiodes (3)
- photoinduced electron transfer (3)
- Anorganische Chemie (2)
- Chili RNA Aptamer (2)
- Deoxyribozymes (2)
- Design (2)
- Dyes (2)
- Epitranscriptomics (2)
- Fluorescence (2)
- G-quadruplexes (2)
- Holothuria spinifera (2)
- J‐aggregates (2)
- LC-HRESIMS (2)
- RNA modification (2)
- RNA-dependent RNA polymerase (2)
- Ruthenium complexes (2)
- UV/Vis spectroscopy (2)
- X-ray crystallography (2)
- absorption (2)
- acid sphingomyelinase (2)
- annulation (2)
- azulene (2)
- boronate esters (2)
- cage compounds (2)
- cerebrosides (2)
- chirality transfer (2)
- click chemistry (2)
- corannulene (2)
- covalent organic frameworks (2)
- crystal engineering (2)
- cyclophanes (2)
- cytotoxic activity (2)
- cytotoxicity (2)
- density functional calculations (2)
- diketopyrrolopyrroles (2)
- dynamic covalent chemistry (2)
- electrocatalysis (2)
- fullerenes (2)
- helicenes (2)
- heterogeneous catalysis (2)
- homogenous catalysis (2)
- hydrocarbons (2)
- hydrogen bonding (2)
- ligands (2)
- lysosome (2)
- marine natural product (2)
- merocyanines (2)
- nanographene (2)
- optical spectroscopy (2)
- organic semiconductors (2)
- organic solar cells (2)
- pentacene (2)
- perylene bisimides (2)
- phosphorescence (2)
- polymerization (2)
- polymers (2)
- porphyrins (2)
- renewable fuels (2)
- ribozymes (2)
- ruthenium (2)
- ruthenium bda complexes (2)
- ruthenium complexes (2)
- singlet oxygen (2)
- site-specific RNA cleavage (2)
- solid-state emitters (2)
- solvent effects (2)
- spectroscopy (2)
- squaraine dyes (2)
- stereochemistry (2)
- streptomyces (2)
- supramolecular polymers (2)
- thermodynamics (2)
- two-photon absorption (2)
- two-photon excited fluorescence (2)
- water (2)
- water splitting (2)
- 2-photon absorption (1)
- ADME analysis (1)
- AIE (1)
- API (1)
- Aldehyde Bioconjugation (1)
- Alkyltransferase Ribozyme SAMURI (1)
- Alzheimer′s disease (1)
- Amplification (1)
- Anchimeric assistance in solvolysis (1)
- Ancistrocladus ealaensis (1)
- Ancistrocladus likoko (1)
- Antiviral nucleoside analogues (1)
- Apoptosis (1)
- Aromatic-hydrocarbon (1)
- Aspergillus niger (1)
- Atomic and molecular interactions with photons (1)
- BMP-2 (1)
- BMP-2 delivery (1)
- Bacillus megaterium (1)
- Baltic Sea (1)
- Bicyclo[1.1.0]butylcarbinyl sulfonates (1)
- Biochemistry (1)
- Biocompatibility (1)
- Biodegradable polymer scaffolds (1)
- Bioorthogonal Tag (1)
- Bone morphogenetic protein-2 (1)
- Bone tissue engineering (1)
- Butadien (1)
- C-13 NMR (1)
- C-C coupling (1)
- CCL2 (MCP-1) (1)
- CD4+ T cells (1)
- CD8+ T cells (1)
- CXCL8 (IL-8) (1)
- Caco-2 (1)
- Carbon (1)
- Ceramide (1)
- Chemical modification (1)
- Chromophore Assembly (1)
- Chromophores (1)
- Co-Crystal Structures of Chili RNA (1)
- Conjugated polymers (1)
- Corannulene (1)
- Cryoelectron Microscopy (1)
- Cryoelectron microscopy (1)
- Cyclobutylcarbinyl sulfonates (1)
- DNA (1)
- DNA catalysis (1)
- DNA/RNA binding (1)
- DNA/RNA sensors (1)
- DNS-Schädigung (1)
- Deoxyribozyme (1)
- Dictyota (1)
- Dictyotaceae (1)
- Dimers (1)
- Donor−acceptor dyads (1)
- EPR (1)
- Effectors in plant pathology (1)
- Electron (1)
- Electron demand in ditosylates (1)
- Electron transfer (1)
- Emission (1)
- Energy transfer (1)
- Enzymes (1)
- Eriodictyon californicum (1)
- FT-IR spectroscopy (1)
- Fiels-effect transistors (1)
- Fluorescence and Crosslinking (1)
- Fluoreszenzresonanz-Energietransfer (1)
- Fluorogenic RNA Aptamers (1)
- Functional nucleic acids (1)
- Functionalization (1)
- Fungal host response (1)
- Garcinia biflavonoids (1)
- Gibbs activation energy (1)
- Glycosyltransferase (1)
- Golgi (1)
- Graphene nanoribbons (1)
- Growth; BMP-2 (1)
- H2A histone family member X (H2AX) (1)
- HIV (1)
- HRMS (1)
- High efficiency (1)
- High performance (1)
- Hyperfine coupling constants (1)
- In-vitro (1)
- Indirect and direct contributions to A<sub>iso</sub> (1)
- Influence of excitation classes (1)
- Intensity (1)
- Isomorphe Nukleobasen-Analoga (1)
- J-aggregate behavior (1)
- J-aggregates (1)
- Jurkat cells (1)
- K-region (1)
- K2–K model (1)
- Lectins (1)
- Light-emitting diodes (1)
- Lippert–Mataga plot (1)
- Liquid-crystalline (1)
- MAS (1)
- METTL8 (1)
- Mandibular continuity defects (1)
- Marcus inverted region (1)
- Marrow stromal cells (1)
- Merocyanine (1)
- Mesenchymal transition (1)
- Microenvironment (1)
- Mitochondrial Matrix Protein (1)
- Modified Nucleotides in tRNAs (1)
- Molecular mechanism (1)
- Molecular-dynamics (1)
- Molecules (1)
- Molnupiravir (1)
- Molnupiravir-Induced RNA Mutagenesis Mechanism (1)
- Multibranched structures (1)
- N-oleoyl serinol (1)
- NDI-H (1)
- NIR OLED (1)
- NMR spectroscopy (1)
- Naphthylisoindolinone alkaloids (1)
- Neisseria (1)
- Nucleic Acids (1)
- Nucleobase Analogue (1)
- OEG chains (1)
- Octavalen (1)
- Oligofructoside (1)
- One-photon (1)
- Optical Spectroscopy (1)
- Optical properties (1)
- Optical spectroscopy (1)
- Oral squamous cell carcinoma (1)
- Organelles (1)
- PBI cyclophane (1)
- PI stacking (1)
- Pathway (1)
- Perovskite (1)
- Phaeophyceae (1)
- Photochemistry (1)
- Photoelektron (1)
- Polymer-drug interaction (1)
- Polymers (1)
- Potential-energy curves (1)
- QM/MM (1)
- RNA Enzymes (1)
- RNA Labelling (1)
- RNA Methyltransferase (1)
- RNA Modification (1)
- RNA aptamers (1)
- RNA labeling (1)
- RNA ligation (1)
- RNA splicing (1)
- RNA-Aptamere (1)
- RNA-Dependent RNA Polymerase (1)
- RU-(II) complexes (1)
- Radical-ion pair (1)
- Rearrangement of carbocations (1)
- Remdesivir (1)
- Ribozyme (1)
- Ru(II)–Fe(II)–Ru(II) complex (1)
- SARS-CoV-2 polymerase (1)
- SARS-CoV2 Replication Impairment (1)
- SacB (1)
- Scleractinia (1)
- Screening (1)
- Simulations (1)
- Sinus floor augmentation (1)
- Site-Specific RNA Cleavage (1)
- Site-specific RNA labelling (1)
- Solution-state NMR (1)
- Spin density (1)
- Squamous-cell carcinoma (1)
- Sracking (1)
- Staphylococcus aureus (1)
- State (1)
- Stereochemistry (1)
- Stokes-Verschiebung (1)
- Stokes-shifted fluorescence emission (1)
- Streptomyces axinellae (1)
- Structural Biology (1)
- Structure elucidation (1)
- Struktursonden (1)
- Stylissa carteri (1)
- Suc1 (1)
- Supramolecular Element (1)
- Suzuki coupling (1)
- Synthetic Functional RNAs (1)
- Systems (1)
- TERRA RNA (1)
- Thalassodendron ciliatum (1)
- Tumorigenicity (1)
- Vibronic contributions (1)
- X-ray Crystallography (1)
- X-ray diffraction (1)
- XNA (1)
- XRPD (1)
- [n]helicenes (1)
- \(\alpha\)-phase (1)
- \(\beta\)-phase (1)
- \(^{1}\)H-\(^{13}\)C HETCOR (1)
- abietane (1)
- activating transcription factor 4 (ATF4) (1)
- adsorption (1)
- aelf-assembly (1)
- alkaloids (1)
- amphiphilic dyes (1)
- amplification (1)
- ancistrocladinium A (1)
- annihilation (1)
- anti-cancer-agent (1)
- anti-depressant drug (1)
- anti-trypanosomal (1)
- antibacterial activity (1)
- antidepressants (1)
- antimicrobials (1)
- aqua material (1)
- aqueous medium (1)
- arene-fluoroarene (1)
- arenes (1)
- aromatic compounds (1)
- artificial base pair (1)
- association (1)
- ataxia teleagiectasia mutated (ATM) (1)
- azaborole (1)
- azaphilone (1)
- azido-ceramides (1)
- bacterial infection (1)
- bartalinia robillardoides (1)
- biflavanoids (1)
- bile salt (1)
- bioactive compound (1)
- bioactivities (1)
- biocatalysis (1)
- biocompatibility (1)
- biological techniques (1)
- biomass (1)
- bioorthogonal SAM analogue ProSeDMA (1)
- bioorthogonal metabolic glycoengineering; click chemistry; sialic acid (1)
- biophysical investigation (1)
- biosynthesis (1)
- bis-terpyridyl ligands (1)
- boric acid (1)
- boron (1)
- boronateesters (1)
- borylation (1)
- brown seaweeds (1)
- bulk-heterojunction solar cells (1)
- carbon (1)
- carrier transport (1)
- cascade reactions (1)
- catalyst (1)
- catalyst synthesis (1)
- catalysts (1)
- catalytic (1)
- catalytic activity (1)
- catalytic mechanisms (1)
- cell membrane model (1)
- cellular stress response (1)
- ceramidase (1)
- ceramide analogs (1)
- cerebroside (1)
- ceriops decandra (1)
- charge transport (1)
- charge transport; hydrogen bonding; oligothiophene; organogel; self-assembly (1)
- chemical modification (1)
- chiral resolution (1)
- circular polarized luminescence (1)
- circularly polarized luminescence (1)
- co-aggregation (1)
- cocrystallization (1)
- colloid (1)
- columnar phases (1)
- complexation (1)
- complexity (1)
- configurational stability (1)
- conjugated molecule (1)
- cooperative self-assembly (1)
- coordination chemistry (1)
- coordination isomerism (1)
- coordination oligomer (1)
- coordination oligomers (1)
- covalent organic framework (1)
- cristal engeneering (1)
- crystalline (1)
- crystals (1)
- curcumin (1)
- curvature (1)
- curved π-systems (1)
- cyclic perylene bisimide (1)
- cyclodehydrogenation (1)
- cylindrical micelles (1)
- cysteine protease (1)
- cytoplasm (1)
- decandrinin (1)
- deoxyribozymes (1)
- deracemization (1)
- di-\(\pi\)-methane rearrangement (1)
- dibenzosemibullvalenes (1)
- differential scanning calorimetry (1)
- diffusion (1)
- dimerization (1)
- dimers (1)
- dinuclear (1)
- dipole-dipole interaction (1)
- discotic liquid crystals (1)
- discovery (1)
- dissolution rates (1)
- disulfide bonds (1)
- docking (1)
- docking studies (1)
- donor-acceptor dyad (1)
- donor-acceptor interactions (1)
- donor–acceptor (1)
- donor–acceptor dyads (1)
- drug delivery (1)
- drugs (1)
- duplex structure (1)
- dye assembly (1)
- dye chemistry (1)
- electrodes (1)
- electronic and spintronic devices (1)
- electronic collective variables (1)
- electronic devices (1)
- electronic structure (1)
- electronic wavefunction (1)
- emission (1)
- enantiomerization (1)
- enantiomers (1)
- encapsulation (1)
- enzyme (1)
- enzyme purification (1)
- enzyme structure (1)
- enzymes (1)
- epitranscriptomics (1)
- ergosterol derivative (1)
- ethenoanthracenes (1)
- excimer (1)
- excimer formation (1)
- extractives (1)
- ferroelectrics (1)
- films (1)
- flavenoids (1)
- flavonoids (1)
- flourescence quantum yield (1)
- fluerescence (1)
- fluorenscence (1)
- fluorescence resonance energy transfer (1)
- fluorescence spectroscopy (1)
- fluorescent (1)
- fluorescent probes (1)
- fluorogen-activating RNA aptamer (FLAP) (1)
- fluoxetine (1)
- flux (1)
- folded macrocyles (1)
- folding (1)
- folding landscapes (1)
- functionalization (1)
- glycocalyx (1)
- glycosphingolipids (1)
- growth (1)
- guttiferae (1)
- hMSC-TERT (1)
- halichondria panicea (1)
- heavy metals (1)
- helicene (1)
- heterocycles (1)
- hexakisadducts (1)
- high-temperature NMR (1)
- homochiral dimer (1)
- host-guest systems (1)
- hybrid materials (1)
- hydrazone (1)
- hydrogen peroxide (1)
- hydroxylation (1)
- imaging (1)
- imidization (1)
- imines (1)
- in vitro Selection (1)
- induced phase transition (1)
- inflammation (1)
- intersystem crossing (1)
- intrinsic free space (1)
- invasion (1)
- inflammatory response (1)
- ion pairing (1)
- iron oxide nanoparticles (1)
- isomorphic nucleobase analog (1)
- key structure - fluorescence activation relationships (SFARs) (1)
- large stokes shift (1)
- laser (1)
- lectin (1)
- ligand binding (1)
- liposome (1)
- liquid crystal alignment (1)
- livingstonei (1)
- luminescent solar concentrators (1)
- macrocycle (1)
- major depression (1)
- marine bacteria (1)
- marine fungi (1)
- marine macroalgae (1)
- marine natural products (1)
- marine sponge (1)
- materials (1)
- materials design (1)
- measles (1)
- mechanism (1)
- merocyanine (1)
- merocyanine dyes/pigments (1)
- mesogens (1)
- metabolic analysis (1)
- metabolic glycoengineering (1)
- metadynamics (1)
- metal complexenes (1)
- metal-to-ligand charge transfer (MLCT) (1)
- metallomacrocycles (1)
- methyl viologen (1)
- methyltransferase (1)
- micelles (1)
- microbiology (1)
- microbiology techniques (1)
- microscopy (1)
- microtubes (1)
- migration (1)
- minimal inhibitory concentration (1)
- mobility (1)
- modified monosaccharides (1)
- molecular (1)
- molecular capsules (1)
- molecular dynamics (1)
- molecules (1)
- multiflora (1)
- multimetallic complexes (1)
- multiple myeloma (1)
- nanoparticles (1)
- nanorods and nanosheets (1)
- nanoscale imaging (1)
- nanosegregation (1)
- nanotube (1)
- naphthalene diimide (1)
- naphthylisoquinoline alkaloid (1)
- naphthylisoquinoline alkaloids (1)
- narrow bandwidth (1)
- natural products (1)
- near infrared emitter (1)
- near-infrared sensitivity (1)
- non-fullerene acceptors (1)
- noncovalent interactions (1)
- nonfullerene acceptors (1)
- nucleation elongation (1)
- nucleation-elongation (1)
- nucleation-elongation model (1)
- nucleic acids (1)
- nucleoside modification recognition (1)
- obstructive pulmonary disease (1)
- oligomers (1)
- oligothiophene (1)
- oligothiophenes (1)
- optical materials (1)
- optics (1)
- organic semiconductors (1)
- organic compounds (1)
- organic light emitting diodes (1)
- organization (1)
- orylation (1)
- oxidation (1)
- oxygen reduction reaction (1)
- p-conjugated systems (1)
- pancreatic cancer (1)
- parallel polar dimers (1)
- pentaketide (1)
- peptide backbone (1)
- perylene (1)
- perylene bisimide dyes (1)
- perylene bisimide hydrogels (1)
- perylene bismide dye (1)
- perylene dyes (1)
- perylene imide (1)
- perylenebisimide (1)
- perylenebisimide dyes (1)
- phenazine (1)
- phenylboronate (1)
- phosphodiesterase-4 inhibitor (1)
- photochemical (1)
- photoconductive interlayer (1)
- photoluminescence (1)
- photoresponsive behavior (1)
- photosenitizers (1)
- photosensitization (1)
- phthalocyanines (1)
- platinum complexes (1)
- pol(2-oxazoline) (1)
- polarizing optical microscopy (1)
- poly(2-oxazine) (1)
- polycycles (1)
- polycyclic aromatic hydrocarbon (1)
- polymer drug interaction (1)
- polymorphism (1)
- polyoxazolines (1)
- polypyridyl complexes (1)
- porous materials (1)
- porousmaterials (1)
- probes (1)
- protease inhibition (1)
- proteasome inhibitor resistance (1)
- proteasome subunit beta type-5 (PSMB5) (1)
- push–pull thienylthiazole (1)
- pyrene (1)
- quantum chemical analysis (1)
- quantum optics (1)
- racemization (1)
- radical (1)
- radical anion (1)
- reabsorption (1)
- real-time NMR spectroscopy (1)
- recombinant proteins (1)
- redox (1)
- regulatory T cells (1)
- regulatory T cells (Treg) (1)
- renew-able fuels (1)
- rhizophoraceae (1)
- rigidification (1)
- rofumilast (1)
- room-temperature phosphorescence (RTP) (1)
- rotational diffusion (1)
- ruthenium catalysts (1)
- sSupramolecular interaction (1)
- scanning probe microscopy (1)
- seagrass (1)
- self-sorting (1)
- separation techniques (1)
- shape-amphiphiles (1)
- short-range order (1)
- sialic acids (1)
- simulated intestinal fluid (1)
- single crystal structure (1)
- site-specific RNA labeling (1)
- social self‐sorting (1)
- solar cells (1)
- solar fuels (1)
- solid-state NMR (1)
- solid-state NMR spectroscopy (1)
- solid‐state emission (1)
- solubility (1)
- solvatochromism (1)
- solvolysis of (1)
- spectroscopic analysis (1)
- sphingolipid expansion microscopy (1)
- sphingomyelinase (1)
- sphingosine (1)
- sphingosine 1-phosphate (1)
- sphingosine kinases (1)
- stability (1)
- star-shaped compounds (1)
- starazine (1)
- starphene analogue (1)
- stereospecific sythesis (1)
- sterubin (1)
- stokes shift (1)
- structural biology (1)
- structural changes (1)
- structural dynamics (1)
- structure probes (1)
- structure probing (1)
- structure–function relation (1)
- structure–property relation (1)
- subphthalocyanine (1)
- superparamagnetism (1)
- superstructure (1)
- supramolecular assembly (1)
- supramolecular folding (1)
- supramolecular materials (1)
- supramolecular polymerization (1)
- surface interactions (1)
- survival (1)
- sustainable energy source (1)
- swallow-tail (1)
- systems (1)
- template catalysis (1)
- tenofovir (1)
- tethya aurantium (1)
- tetracoordinated boron (1)
- tetromycin (1)
- theranostics (1)
- thin-film transistors (1)
- time-resolved impulsive stimulated raman spectroscopy (1)
- tissue engineering (1)
- transient absorption (1)
- triarylamine (1)
- triarylborane (1)
- trinuclear (1)
- triplet (1)
- triplet sensitization (1)
- two-dimensional nanostructures (1)
- umbrella-shaped mesogens (1)
- upconversion (1)
- upramolecular polymerization process (1)
- vacuum processable (1)
- vibrational coherence (1)
- viral epidemiology (1)
- viral infection (1)
- water oxidation catalysis (1)
- zooxanthellae (1)
- π-conjugated systems (1)
- π-extension (1)
- π-π-interactions (1)
- π–π Stacking (1)
Institute
- Institut für Organische Chemie (243) (remove)
Sonstige beteiligte Institutionen
- Agricultural Center, BASF SE, 67117 Limburgerhof, Germany (1)
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells, Göttingen (1)
- Department of Cellular Biochemistry, University Medical Center Göttingen (1)
- Department of Cellular Biochemistry, University Medical Centre Göttingen (1)
- Department of Molecular Biology, University Medical Centre Göttingen (1)
- Georg August University School of Science (1)
- Göttingen Center for Molecular Biosciences, University of Göttingen (1)
- Helmholtz Institute for RNA-based Infection Biology (HIRI), Josef-Schneider-Straße 2/D15, DE-97080 Wuerzburg, Germany (1)
- Institut für Molekulare Infektionsbiologie (MIB) der Universität Würzburg (1)
- Institute of Cancer Research (ICR) London (1)
The 130 chemical shifts were determined of the carbons in 12 cycloheptanes, 21 cycloheptanols, and 8 cycloheptanones. In some cyc1oheptanols and cyc1oheptanones, the assignments have been obtained unambiguously by the synthesis of deuterated derivatives and the use of paramagnetic-shift reagents. Substituent effects for the different types of groups have been calculated. The most informative data about the cyc10heptane conformations were provided by the relatively well understood I' effects. The results are generally in,good agreement with predictions based on the twist-chair form, which has been predicted by Hendrickson to be the most stable conformation. Pairs of cis-trans isomers are found to have rather characteristic differences in their 130 spectra. This fact was used to assign the resonances found for cis-trans mixtures of methyl-substituted cyc1oheptanols to specific isomers.
Via reduction of benzvalene (1) with diirnine tricyclo[3.1.0.02•6]hexane is obtained in good yield. The procedure renders 3, which has already been synthesized by Lemal and Shim, accessible much easier and in larger quantities. IH and 13C n.m.r. spectroscopic data are discussed. Both the thermal and the AgBF4-catalyzed rearrangernent of 3 yield 1,3-cyclohexadiene (8). - The ozonolysis of 1 with subsequent LiAIH4-reduction results in cis-I,3- bis(hydroxyrnethyl)cyclobutane (13a).
Carbon-13 shieldings and one-bond \(^{13}\)C-H coupling constants of bicydo[2.1.1]hexane, bicydo[2.l.l]hex- 2-ene, tricydo[3.1.1.0\(^{2.4}\)]heptane and benzvalene are presented and compared. to the data of related. compounds. H a bicydo[3.1.0]hexane system is part of a rigid skeleton, the cydopropane ring exerts spedfk: 'Y substituent eflects of two ldnds. In the case of the bicyclobexane boat form an upfield shift of the C-3 signal is observed and in tbe esse of the chair form a downfield shift of 15-20 ppm. Compared to the corresponding cydopentanes the double bond in strained cydopentenes causes downfield shifts of the C-4 absorption. 1bis eftect increases witb increasing strain, reaching 8 45.9 ppm maximum in benzvalene. Hence it is tbe only known bicydo[l.l.O]butane baving 8 reversed order of carbon shieldings. The downfield shifts are e:xplained by means of simple orbital interaction schemes.
By means of the BC NMR spectra of tricyclo{2.2.0~rfJ6Jhexane and thirteen of its derivatives the effects of substituents in endo-3- and endo-5-positions on the HC chemical shifts have been determined. The y-anti effects are at least as Jarge as in monosubstituted cyc1obutanes, where the shielding values of second-row hetero substituents exceed those in unstrained systems by far, and higher-row and carbon substituents still cause substantial upfield shifts. In the title system the y-anti effect of a substituent in the endo-3- and endo-5-position are operative additively, and thus shift the absorption of C-J upfieJd by a maximum of 27 ppm with respect to the unsubstituted hydrocarbon.
The He (I) photoelectron spectra of 2-bicyclo[2.1.l]hexene (1), 2,3-bis(methylene)bicyclo[2.1.l]hexane (3), and 3,4-bis(methylene)tricyclo[3.l.O.0\(^{2.6}\)]hexane (4) have been investigated. The assignment given is based on a ZDO model and semiempirical calculations. Tagether with the PE data of benzvalene (2), the reported data allow a comparison between 1-2 and 3-4. This yields a measure of the interactions between 8 cyclobutane or 8 bicyclobutane moiety and a double bond system within a ZDO model. The resonance integral found in the case of 1 and 3 amounts to -1.9 eV, that for 2 and 4, to -2.3 eV. The investigations furthermore reveal that the electronic factors which contribute to the higher reactivity of the bicyclobutane compounds amount to 5 kcal/mol.
Large-acale multi-reference configuration interaction (MRD-CI) calculations in a quite flexible AO basis are employed to study the energy hypersurface for the reaction intermediates XC\(_3\)H\(_4\) with X = Cl, Br and F. Particular emphasis is therby placed on determining the equilibrium conformations, the CH\(_2\) rotation barrier and the energy surface for a possible bridging (shuttling motion (1a] of X between the two carbon centers). The absolute minimum in the potential energy surface is found in all three cases for the asymmetric ß-halo radical in general agreement with ESR data at an XCC angle of ca. 110°, a c-c separation somewhat shorter than a single bond and an approximate sp3 type hybridization (\(\alpha _2 \approx \) 135-140°). In FC\(_2\)H\(_4\) the energy difference between the minimum in the symmetric conformation and the absolute minimum is found to be more than 30 kcal so that shuttling seems impossible in agreement with experimental findings. In BrC\(_2\)H\(_4\) the difference between these two potential minima is only between 1-2 kcal, i.e., smaller than the barrier to CH\(_2\), rotation, so that· shuttling is favored, while ClC\(_2\)H\(_4\) takes an intermediate position between these extremes. The use of correlated wavefunctions is found to be quite important for such a study; the results are related to various kinetic studies of these radicals.
The He I photoelectron (PE) spectra of octavalene (5) as weil as its hydrogenated products 6-8 have been investigated. The assignment given is based on an empirical comparison of 5-8 with related compounds, a ZDO model, and semiempirical and ab initio calculations. Within the ZDO model the interaction between the buta.diene moiety and the bicyclobutane fragment of 5 is described by a resonance integral of -2.3 eV. The orbitalsequence of 5 is found tobe 2a\(_2\) (\(\pi\)-\(\sigma\)), 9a\(_1\) (\(\sigma\)), 3b1 (\(\pi\) - \(\sigma\)), 1a\(_2\) (\(\sigma\) + \(\pi\)), 2b\(_1\) (\(\sigma\) + \(\pi\)).
The hyperfine coupling constant for the nitrogen atom is evaluated by large-scale MRD-CI calculations. A detailed analysis of the charge density at the nucleus and the spin polarization in the ls and 2s shell as a function of various technical parameters is undertaken. Various (s, p) AO basis sets and the inftuence of correlation orbitals is investigated as weil as selection threshold and other properlies in CI calculations. The best value, obtained for the isotropic hyperfine coupling constant in an s, p, d basis, based on theoretical judgment of' best' quantities, is 9·9 MHz compared to 10·4509 MHz.
Reaktionen von 1,3-Butadien und einigen seiner Methylderivate mit 1a und 1- Methyl-1,2-cyclohexadien 1b sowie den Übergang der [2 + 2]-Cycloaddukte 2 und 3 in das bisher unbekannte 1,2,3,5,8,8a-HexahydronaphthaJin 4a und einige seiner Methylderivate
Abstraction of an allylic hydrogen atom in homobenzvalene (4) either in solurion by photolyticaßy generated tert-butoxyl radicals or in an adamantane matrix by X-rays produces the homobcnzvalenyl radical (5). which tbennally rearranps · to tbe tropylium ndical (1). In solution tbe activation cnergy for the rate determined step of the reaction sequence was detennined· to be 13.4 ± O.S kcal/mol.
Study of the 1s and 2s shell contributions to the isotropic hyperfine coupling constant in nitrogen
(1988)
The istropic part of the hyperfine coupling constant is investigated by means of multireference configuration interaction calculations employing Gaussian basis sets. A detailed study of the 1s and 2s spin polarisation in the nitrogen atom and the NH molecule shows that the structure of the lower-energy space of the unoccupied orbitals is essential for the results. A contraction of the Gaussian basis is possible without loss of accuracy if enough flexibility is retained to describe the main features of the original space of unoccupied functions. Higher than double excitations are found to be non-negligible for the description of α\(_{iso}\).
Diels-Alder reaction of dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate (5) with benzvalene (4), norbornene, and norbornadiene afforded the azo compounds 7 and 8. Theseare derivatives of 2,3-diazabicyclo[2.2.2]oct-2-ene as is azo compound 3, which had been obtained previously from 5 and 2 equiv of benzvalene (4). The photochemical extrusion of nitrogen from 3, 7, and 8 has been studied. Whereas 7 and 8 on direct irradiation in benzene gave rise exclusively to the bicyclo[2.2.0]hexane derivatives 9 and 10, respectively, from 3 in addition to the bicyclo[2.2.0]hexane 11, the diolefin 1l was formed. Diolefin 12 has cisdouble bonds in the nine-membered ring and is fixed in a boat conformation in a manner so that the two bicyclobutane systems approach each other very closely. This geometry suggests the unusual ring opening of the intermediate 1,4-cyclohexanediyl diradical from a boat conformation, which arises by inversion of the primarily generated boat conformation. Sensitized photolysis of 3 as weilasthat of ll produced the saturated isomer 13 of 11 and 12. The proximity of the bicyclobutane systems in 1l causes unprecedented reactions leading to cage compounds. When ll was heated at 90 °C, a rearrangement to the pentacyclic product 10 took place. Utilization of tetradeuteriated substrate ll-d4 supported a pathway with two diradical intermediates. Behaving in a convcntional manncr, bicyclobutane 9 and bis(bicyclobutane) 11 took up 1 and 2 equiv of thiophenol most probably in a radical-chain addition to give the thioethers 28 and 19, respectively. In contrast, bis(bicyclobutane) ll was converted by 1 equiv of thiophenol into cagc compound 30 in a process involving both the strained a systems. Heating at 80 °C subjected 30 to a reversible Copc rearrangement, resulting in a 6:1 mixture of 31 and 30. When it was treated with bromine, 11 was transformed to cage compound 38. This addition is believed to proceed via a cationic intermediate. The structure of cage compound 10 was established by a singlc-crystal X-ray analysis of dialcohol 11 prepared from 20 and methyllithium.
Large-scale multireference configuration interaction (MRD-CI) calculations in a quite flexible AO basis are employed to study the energy hypersurface for the reaction intermediate FC\(_2\)H\(_4\) • The reaction F + C\(_2\)H\(_4\) -> FC\(_2\)H\(_4\) as weil as the 1,2 migration of the fluorine atom in FC\(_2\)H\(_4\) is investigated. In addition the rotation around the CC bond in the optimum conformation is studied. The absolute minimum in the potential energy is found for the asymmetric structure but the symmetric structure is also found to be stable with respect to the dissociation, so that a shuttling of the fluorine atom is in principle possible but highly unlikely because ( l) the activation energy is high ( II 5-130 kJ fmol) and the saddle point lies only 4(}-50 kJ jmol below the dissociation Iimit of F + C\(_2\)H\(_4\) and (2) the competitive motion, i.e., rotation around the CC axis, is nearly free (I 1-17 kJ/mol).
The hyperfine coupling constants for the \(^3\)Σ\(-\) ground state of the NH molecule are determined by configuration interaction calculations whereby the infl.uence of polarization functions as weil as of the configuration space on the spin polarization mechanism is analysed. The dipolar part Au(N) and Au(H) can be obtained very reliably without much computational effort (A .. (N) == -45·3 MHz and A"(H) = -62·3 MHz). The value for the isotropic contribution a1.., in the best AO basis and MRD-CI treatment is - 64·5 MHz for H and 16·6 MHz for nitrogen compared to the corresponding experimental quantities of -66 MHz and 19 MHz respectively. Their determination depends on a subtle balance of the lu, 2u and 3u shell correlation description, whereby the dominant contribution to a1..,(H) results from the 2u shell. It is shown that the often good agreement of a110 values with experiment in a small basis singledouble configuration interaction treatment results from a cancellation of two errors.
Multi-reference configuration interaction calculations employing various orbital transformations are undertaken to obtain the isotropic hyperfine coupling constant a\(_{iso\) in nitrogen and a\(_{iso\) (H) in the CH molecule. The natural orbital (NO) basis is found to be more effective than the simple RHF-MO basis; the most obvious is a basis of spin natural orbitals (SNO). It is found that a\(_{iso\) is approached from opposite sides in the NO and 2s shell SNO basis if the CI expansion is increased. Both results are within a few percent of the full CI Iimit for the nitrogen atorn (in the given AO basis) and the experimental value for Hin the CH radical. Various features ofthe SNO are discussed.
The isotropic (a\(_{iso}\)) and dipolar (A\(_{dip}\)) hyperfine coupling constants of 19F2 were obtained from MRD-CI wave functions using a variety of basis sets. In series I, increasing numbers of d functions were added to a 5s4p contracted Huzinaga!Dunning basis. In series II, the 5s3p basis set was uncontracted in several steps until 9s5p was reached, to which were added from one to three d-polarization functions. Cl parameters (selectioo threshoids and the number of reference coofiguratioos) were also varied. A study of the R dependence of aiso and Adip was perfonned. The best values obtained at R\(_e\) are 260 G for a\(_{iso}\) and 308 G for A\(_{dip}\)• compared with experimental values of about 280 G for a;10 and 320 G for A\(_{dip}\)·
The cycloadducts 6 and 7 of tricyc1o[4.1.0.0 2 ,7)hepta- 3,4-diene (~) with styrene and 1,3-butadiene rearrange to unusual products on thermolysis, namely the cycloheptatriene derivatives ~ and 10. 1-0xa-3,4-cyclohexadiene (20) is generated smoothly from 6,6-dichloro-3-oxabicyclo[3.1.0]hexane (22) and n-butyllithium. 1-0xa-2,3-cyclohexadiene (11) is formed from 6-exo-bromo-6-endo-fluoro-2-oxabicyclo[ 3.1.0]hexane (30) and methyllithium. In the presence of activated olefins, this reaction provides an efficient route to 28 and 33 - 38, the trapping products of 21. Interestingly, [2+2]-cycloadditions do not take place at the same double bond of 21 as [4+2]-cycloadditions. The reactions of 1,3-cyclopentadiene and indene with bromofluorocarbene afford 6-exo-bromo-6-endo-fluorobicyclo[3.1.0]hex-2-ene (50) and its benzo derivative ~, respectively. On treatment of these compounds with methyl lithium in the presence of styrene, the interception products 53 and 47 of 1,2,4-cyc10- hexatriene (44) and its benzo derivative 43, respectively, are formed in good yields.
Large-scale multireference configuration interaction calculations in a double·t·type AO basis including polarization functions are carried out for the potential surface of the ClC\(_2\)H\(_4\9 system. The charge distribution for various extreme points of the surface is discussed. The absolute minimum is found for an asymmetric ClC2H4 structure. The symmetrical bridged nuclear conformation is also found to be stable with respect to dissociation into Cl + C\(_2\)H\(_4\)• The activation energy for rotation about the C-C axis is calculated tobe around 18 kJ/mol, which is comparable tothat for the 1,2 migration {around 26 kJ/mol). The stereochemistry is governed by the fact that addition of CI to C\(_2\)H\(_4\) (or dissociation) is a two-step reaction proceeding through a symmetrica1 intermediate. The direct addition pathway possesses a small barrier of about 8 kJ jmol.
The transient yellow color observed in the cycloaddition of homobenzvalene (HB) with tetracyanoethylene (TCNE) is associated with the charge-transfer complex [HB, TCNE). The deliberate photoexcitation of [HB,TCNE) affords a mixture of charge-transfer cycloadducts (1, 2, and 3) that differs from that obtained in thermal cycloaddition. The relationship of {HB t TCNE•) radical-ion pair (as the critical reactive intermediate in charge-transfer cycloaddition) to the activation process for thermal cycloaddition is discussed.
Potential energy and spectroscopic constants for the X\(^2 \sum^+ _\mu\) ground state of a;, were calculated by configuration-interaction (Cl) methods, using large basis sets with polarization and diffuse functions. From these CI wavefunctions, the isotropic (a\(_{iso}\)) and dipolar (A\(_{dip}\)) components of the hyperfine coupling constant were obtained. The effects of various s, p basis sets, polarization and diffuse functions, as well as the influence of reference configurations and configuration selection thresholds were investigated. The best values obtained are 35·31 G for a\(_{iso}\) and 29·440 for A\(_{dip}\)• tobe compared with experimental values of 37 ± 1 G and 32 ± 1 G, respectively. It is shown that the contributions to a1so of the K and L shells are opposite in sign, differing by about 4 G. Upon vibrational averaging, both a\(_{iso}\) and A\(_{dip}\) move towards smaller values as v increases. An adiabatic electron affinity of 2·46eV was obtained for CL\(_2\) , and a vertical electron detachment energy of 3·71 eV for Cl;.
Study of the hyperfine coupling constants of the moleculs NH<sub>2</sub>, NHD and ND<sub>2</sub>
(1990)
In the present paper we c:alculate tbe magnetic hyperfine couplina constants (hfcc) ai.ID and A11 of the ground states of the isotopes NH2, NHD and ND2 using truncated MR..CI methods. Differences from other theoretical methocls and shortoominp of the truncated Cl approach in calculating tlj10 are studied. Polarization effects wbich detennirae ailo. as weU as a simple model to describe the dipolar hfcc's, are discussed. All results are in. excellent aareement with experimental data. lt is shown that ab initio methods are able to obtain reliable values for otf-diaaonal values of A41 which are difficult to measure experimentaDy.
Dipole moments and various spectroscopic constants of some low-lying electronic states of the CaF molecule have been calculated using the multireference single· and double-excitation configuration-interaction (MRD-CI) method. The electronic structure of the highly ionic molecule in various excited states can be explained in tenns of different polarisations of the mainly Cacentered valence electron in the field of the F\(^-\) anion. Plots of natural orbitals occupied by the valence electron in the different states give a qualitative picture of the charge distribution and provide a visualisation of the different polarisations of the valence electron in the various states. Comparisons with the electrostatic polarisation model ofTörring, Ernstand Kändler (TEK model) are made. The unknown A' \(^2 \Delta\) state is predicted to lie about 21200 cm\(^{-1}\) above the ground state.
Reliable prediction of the isotropic hyperfine coupling constant, a\(_{iso}\), is still a difficult task for ab initio calculations. Strong dependence on the method used for its calculation is found. Within a truncated multi-referencc ansatz a\(_{iso}\) is strongly affected by the size ofthe reference space and the nurober of terms in the truncated Cl expansion. In the present paperdifferent effects of the neglected Cl space are discussed. Modified B\(_K\) and A\(_K\) methods are used to estimate the contributions ofthe neglected configurations. lt can be shown that a combination of both methods is able to recover about 90-9 S% of the total error in a\(_{iso}\)· Furthermore, it was found that to obtain about 90% of the B\(_K\) correction only about I 0-20% ofthe configurations within H0 have to be corrected.
The hyperfine coupling constants (isotropic hfcc and four Cartesian components of the ani~ tropic tensor) are calculated for all three atoms of C\(_2\)H in its three lowest-lying electronic states at various molecu)ar geometries by means of the ab initio configuration interaction ( MRO.CI) method. The off-diagonal electronic matrix elements involving the two species ofthe A' symmetry are also computed. A diabatic transforrnation is perforrned Jeading to simple geometrical depen· dences of the hyperline coupling constants.
The vibronically averaged values for tbe hyperfine coupling constants in the X\(^2 \sum\)-A\(^2 \Pi\) system of the ethynyl radical are computed by means of tbe ab initio metbod calculations. The results point at tbe importance of taking into account the coupling of a1l tbree electronic states in question ( I\(^2\)A', 2\(^2\)A', and 1\(^2\)A") for a reliable explanation of the available experimental findings. The mean values of the hfcc's for K = 0 and 1 levels in \(^{13}\)C\(_2\)H and \(^{13}\)C\(_2\)D in the energy range up to 6000 cm\(^{-1}\) are predicted.
Large-scale multireference configuration interaction (MRD-CI) calculations in a flexible atomic orbital (AO) basis are employed to study the reaction of C\(_2\)H\(_4\) with CH\(_2\) in its firSt triplet and singlet state. The minimum energy path (MEP) of both reactions is calculated, and different mechanisms are discussed. To examine the possible participation of the singlet state in the overall reaction starting from the triplet channel and terminating in the singlet-state c-C\(_3\)H\(_6\), various cuts through both hypersurfaces are calculated. lt is found that favorable interconversion from the trip1et to the singlet surface can only occur at !arge separations of the two fragments of CH2 and C\(_2\)H\(_4\). Experimental data considering the vibrational motion of CH\(_2\) in connection with the relative position of both surfaces are used to obtain an estimate for the overall barrier of the reaction. The height of the barrier is about 6 kcal/mol, while the barrier of the pure triplet reaction is calculated to be 7-9 kcal/mol.
The hyperfine coupling constants (hfcc) A\(_{iso}\) and A\(_{ij}\) are calculated for the atoms of NH\(_2\) in its, two lowest-lying electronk states at various molecular geometries by means of the ab initio multireference configuration interaction .method. The vibronically averaged values of the hfccs for the K = 0 and 1 levels in \(^{14}\)N \(^1\)H\(_2\) in the energy range up to 20 000 cm\(^{-1}\) are computed. Polarization elfects which determine A\(_{iso}\) as well as a simple model to describe the dipolar hfccs are discussed. All resrilts are in excellent agreement with experimental data.
Vibronically averaged values for K =0 and K = 1 bending levels in the energy range between 0 and 25 000 cm\(^{-1}\) are computed for the \(^{14}\)N, H, and D atoms in NH\(_2\), NHD, and ND\(_2\) The pure ab initio electronic potentials, as well as those derived by fitting of experimentally observed band positions are employed. Effects of vibronic coupling and local perturbations of close-lying levels belanging to different electronic states are discussed.
We have investigated theoretically the importance of the O(\(^3\)P)+CH(a\(^4\sum^-\)) and the O(\(^3\)P)+CH(X\(^2\Pi\)) channels in the collinear chemi-ionization reaction O+CH->HCO\(^+\) +e\(^-\). We have found that both channels may lead to chemi-ionization via favorable Franck-Condon overlaps with the states ofthe ionic species.
Reliable prediction of the isotropic hyperfine coupling constant A\(_{iso}\) is still a difficult task for ab initio calculations. Strang dependence on the method employed for its ca1culation has been found. Within a CI ansatz A\(_{iso}\) is considerably affected by the excitation classes taken into account within the CI calculation. In the present work the influence of various excitation classes on A\(_{iso}\) is examined. Calculations including all single, double, triple and a large part of the quadruple excitations are performed and the individual effects of the excitation classes are studied. It is found that the surprisingly good agreement found for S-CI treatments is due to large error cancellations. The importance of higher than double excitations arises from their indirect influence on the single excitations.
Wben irradiated at 360 nm, furocoumarins with a hydroperoxide group in a side chain effciently give rise to a type of DNA damage that can best be explained by a photoinduced generation of hydroxyl radicals from the excited pbotosensitizers. The observed DNA damage profiles, i.e. the ratios of single-strand breaks, sites of base loss (AP sites) and base modifications sensitive to fonnamidopyrimidine-DNA glycosylase (FPG protein) and endonuclease m, are similar to the DNA damage profile produced by hydroxyl radicals generated by lonizing radiation or by xanthine and xanthine oxidase in the presence of Fe(III)-EDTA. No such damage is observed with the corresponding furocoumarin alcohols or in the absence of near-UV radiation. The damage caused by the photo-excited hydroperoxides is not influenced by superoxide dismutase (SOD) or catalase or by D2O as solvent. The presence of t-butanol, however, reduces both the formation of single-strand breaks and of base odifications sensitive to FPG protein. The cytotoxicity caused by one of the hydroperoxides in L5178Y mome lymphoma cells is found to be dependent on the near-UV irradiation and to be much higher than that of the corresponding alcohol. Therefore the new type of photoinduced damage occurs inside cells. Intercalating photosensitizers with an attached hydroperoxide group might represent a novel and versatile class of DNA damaging agents, e.g. for phototherapy.
Highly reactive methanesulfonates (mesylates, ROMs) have been prepared from 1-phenylethanol. cyclohex-2-en-1-ol, diphenylmethanol and p-methoxybenzyl alcohol by treatment with methanesulfonyl chloride and triethylamine in dichloro- or trichloro-methane at - 20 to 0 °C. The mesylates. characterised in solution by \(^1\)H and \(^{13}\)C NMR at -20 °C, were obtained in satisfactory purity (ca. 95%) in cold solutions but they decomposed by reaction with chloride, triethylamine or the parent alcohol. Rate constants for solvolyses in aqueous acetone and aqueous ethanol have been determined by a fast response conductimetric method. Product selectivities for solvolyses of pmethoxybenzyl mesylate in aqueous ethanol and methanol at 0 °C have been determined by HPLC. From additional new or Iiterature kinetic data for solvolyses of corresponding bromides. chlorides and p-nitrobenzoates (OPNB). Br/CI. OMs/Br and OMs/OPNB rate ratios were calculated; the results are consistent with electronic effects stabilising the carbocationic transition states and increasing OMs/Br rate ratios for these SN 1 solvolyses; none of the evidence supports a geminal electronic effect on Br/CI rate ratios (e.g. caused by stabilisation of the initial state in pmethoxybenzyl chloride). Steric effects on ester /halide rate ratios for solvolyses of tertiary substrates are confirmed. Relative rates over a 10\(^{16}\) range for ester and halide leaving groups are evaluated for solvolyses of 1-phenylethyl substrates in 80% ethanol-water. updating previous work by Noyce et al. (1972).
Density functional theory is applied to the calculation ofthe isotropic byperfine coupJing constants in some small molecules. Various functionals are tested. The agreement of the calculated values to experimental data and values obtained from sophisticated ab initio methods depends on the functionals used and the system under consideration. With respect to spin density calculations the functional of Lee, Yang and Parr with Becke's excbange functional (BLYP) is found to give good results for tbe heavier center of the CH and the NH molecule, while the spin densities of other molecules such as OH, H\(_2\)CN, H\(_2\)CO\(^+\), NO and O\(_2\) deviate considerably from experimental and/or other theoretical results (30%-60%). In cases where the singly occupied orbital can contribute to the isotropic hyperfine coupling constants, accurate results are obtained. The reason fortbis is analyzed.
Various structural possibilities for Si\(_3\)C\(_3\) clusters are investigated by ab initio calculations employing basis sets of double- and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Piesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A "pyramidlike" structure with various multicenter bonds, followed by a es symmetric isomer closely related to the ground state Si6 structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si - C-C-C-Si -Si structure, which is calculated to lie about 38 kcalfmole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities.
The minimum energy path for the reaction O(\(^3\)P\(_g\)) + C\(_2\)H\(_4\)(\(^1\)A\(_g\)) has been calculated by optimizing all relevant geometrical parameters along the approach of oxygen to ethene. A barrier of 4.7 kcal/mol in the \(^3\)A"( ... 9a'\(^2\)- 10a'3a") potential energy surface and an energy difference of 14.4 kcal/mol between the product and the fragments is found at the multireference-configuration interaction level. The corresponding values at the lower-level treatment CASSCF are 9 kcal/mol for the barrier and 9 kcal/mol for the depth of the potential; this shows the importance of inclusion of electron correlation. The barrier for CH\(_2\) rotation for the lowestenergy structure (asymmetric OC\(_2\)H\(_4\)) is around 5 kcal/mol. The energy gap to the first excited state \(^3\)A'( ... 9a'l0a'3a'12) is found tobe 3.6 kcal/mol in MRD-CI calculations at the ground-state minimum. Comparison with \(^3\)CH\(_2\) + C\(_2\)H\(_4\) shows that in this system the lowest-energy surface is \(^3\)A', i.e., the state which is the excited state in 0 + C\(_2\)H\(_4\). This difference in energy ordering of \(^3\)A' and \(^3\)A" states results from the fact that the p\(_x\), p\(_y\), p\(_z\) degeneracy of oxygen orbitals is lifted in \(^3\)CH\(_2\)leading to b\(_1\), b\(_2\). and a\(_1\) MOs whereby the lowest b\(_2\) (a") remains doubly occupied; as a consequence, the reaction pattem between the oxygen and \(^3\)CH\(_2\) approach is different, which is also quite apparent in the calculated charge transfer.
Results ofan ab initio study ofthe hyperfine structure of the X\(^2\)A', A\(^2\) A" ( 1\(^2 \Pi\)) system ofthe formyl radical are presented. Special attention is paid to the analysis of the interplay between the vibronic and magnetic hyperfine etfects. The results of computations are in very good agreement with the available experimental findings. The values for the hyperfine coupling constants in lower bending Ievels of both electronic species are predicted.
A comparative ab initio study of the Si\(_2\)C\(_4\), Si\(_3\)C\(_3\), Si\(_4\)C\(_2\) clusters
(1994)
Various structural possibilities for the Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order M0ller-Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si\(_3\)C\(_3\) clusters is found to be fully operative for Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters. A comparison of the structure and stability of various geometrical arrangements in the series C\(_6\) , Si\(_2\)C\(_4\) , Si\(_3\)C\(_3\) , Si\(_4\)C\(_2\), and Si\(_6\) shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent Si\(_6\) structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding.
The hyperfine structures of the isoelectronic molecules CCO. CNN, and NCN in their triplet ground states (X\(^3 \sum ^-\)) are investigated by means of ab initio methods. The infrared frequencies and geometries are detennined and compared with experiment. Configuration selected multireference configuration interaction calculations in combination with perturbation theory to correct the wave function (MRD-CI/B\(_K\)) employing extended atomic orbital (AO) basis sets yielded very accurate hyperfine properties. The theoretical values for CCO are in excellent agreement with the experimental values determined by Smith and Weltner [J. Chem. Phys. 62,4592 (1975)]. For CNN, the first assignment of Smith and Weltner for the two nitrogen atoms has to be changed. A qualitative discussion of the electronic structure discloses no simple relation between the structure of the singly occupied orbitals and the measured hyperfine coupling constants. Vibrational effects were found to be of little importance.
A reliable prediction of the isotropic hyperfine coupling constant A\(_{iso}\) is still a difficult task for ab initio calculations. In previous studies, the configuration selected multireference configuration interaction method in combination with perturbation theory to correct the wave function (MRCI/ B\(_K\)) yielded accurate isotropic hyperfine coupling constants very economically. The present study gives a detailed analysis of the MRCI/ B\(_K\) method based on the X\(^2 \pi\) state of CH as a test case. Furthermore, a comparison to various other methods such as Maller-Ptesset perturbation theory and the coupled cluster approach is made. The success of the MRCI/ B\(_K\) method in predicting isotropic hyperfine coupling constants is explained in terms of the inßuence of higher than double excitations.
The hyperfine structure of the two isoelectronic molecules H\(_2\)CN and H\(_2\)CO\(^+\) in their electronic ground state (X\(^2\)B\(_2\)) is studied. The influence of the atomic orbital (AO), basis sets, of the correlation treatment, and of the. equilibrium geometry on the obtained hyperfine propertles 1s - investigated. It is found that the multireference double excitation-configuration interaction (MRD-CI)/ BK treatment in which an MRD-CI wave function is corrected by a modified B\(_K\) method yields equivalent results to quadratic CI [QCISD(T)], coupled cluster single doubles [CCSD(T)), or Brueckner doubled [BD(T)]. Uncertainties in the equilibrium geometries are found to be the major source for discrepancies between theoretically and experimentally determined isotropic hyperfine coupling constants (hfccs). For the heavier centers, the calculated values of the isotropic hfccs agrees nearly perfectly with experimental values (\(\approx\) 1%-2%). The calculated values for the hydrogens are too low, but using the equilibrium structure suggested by Yamamoto and Sato [J. Chem. Phys. 96, 4157 ( 1992)], the best estimate deviates by less than 3%.
In the present work the dimethylamino radical ( ( CH\(_3\)) \(_2\)N) and its protonated cation ( ( CH\(_3\))\(_2\)NH\(^+\)) are investigated by means of ab initio methods. The geometries of various conformations of both compounds are obtained with UMP2/6·31 G** calculations, while the hyperfine structure and its dependence on the geometry is studied using the MRD-Cl/B\(_K\) method. The two molecules are compared to study the inftuence of the protonation on geometry and hyperfine structure. The effects of the rotational barriers on the hyperfine structures of (CH\(_3\))\(_2\)N, (CH\(_3\)CH\(_2\))\(_2\)N and ( (CH\(_3\))\(_2\)CH)\(_2\)N will be discussed.
The energy difference between the three lowest-lying isomers of C\(_6\) the linear \(^3 \sum ^-\) state and the two ring forms,the benzene structure (\(^1\)A\(_{18}\)) possessing D\(_{6h}\) symmetry and a distorted cyclic form ( \(^1\)A'\(_1\), D\(_{3h}\) symmetry) have been calculated using various ab initio methods. Variational methods such as multireference configuration interaction (MR-CI) and complete active space second order perturbatiOn treatment (CASPT2) have been applied, as weil as perturbational treatments and coupled cluster calculations (CCD). The correlation of all valence shell electrons is found to be important for a balanced description of the isomers of C\(_6\) . Methods which do not account for higher-order effects appropriately proved to be unsuitable for calculating the energy difference correctly. The results from multireference configuration interaction methods show that the isomers are close in energy with the cyclic forms somewhat lower than the linear form. The ring form possessing D\(_{3h}\) symmetry (\(^1\)A'\(_1\)} is found tobe the lowest-lying structure.
Sialic acids are located at the termini of mammalian cell-surface glycostructures, which participate in essential interaction processes including adhesion of pathogens prior to infection and immunogenicity. Here we present the synthesis and bioorthogonal metabolic incorporation of the sialic acid analogue N-(1-oxohex-5-ynyl)neuraminic acid (Neu5Hex) into the cell-surface glycocalyx of a human larynx carcinoma cell line (HEp-2) and its fluorescence labelling by click chemistry.
A bis(trialkoxybenzamide)-functionalized quaterthiophene derivative was synthesized and its self-assembly properties in solution were studied. In non-polar solvents such as cyclohexane, this quaterthiophene π-system formed fibril aggregates with an H-type molecular arrangement due to synergistic effect of hydrogen bonding and π-stacking. The self-assembled fibres were found to gelate numerous organic solvents of diverse polarity. The charge transport ability of such elongated fibres of quaterthiophene π-system was explored by the pulse radiolysis time resolved microwave conductivity (PR-TRMC) technique and moderate mobility values were obtained. Furthermore, initial AFM and UV-vis spectroscopic studies of a mixture of our electron-rich quaterthiophene derivative with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) revealed a nanoscale segregated assembly of the individual building blocks in the blend.
Four new tetromycin derivatives, tetromycins 1-4 and a previously known one, tetromycin B (5) were isolated from Streptomyces axinellae Pol001(T) cultivated from the Mediterranean sponge Axinella polypoides. Structures were assigned using extensive 1D and 2D NMR spectroscopy as well as HRESIMS analysis. The compounds were tested for antiparasitic activities against Leishmania major and Trypanosoma brucei, and for protease inhibition against several cysteine proteases such as falcipain, rhodesain, cathepsin L, cathepsin B, and viral proteases SARS-CoV M(pro), and PL(pro). The compounds showed antiparasitic activities against T. brucei and time-dependent inhibition of cathepsin L-like proteases with K(i) values in the low micromolar range.
Background: Xenobiotics represent an environmental stress and as such are a source for antibiotics, including the isoquinoline (IQ) compound IQ-143. Here, we demonstrate the utility of complementary analysis of both host and pathogen datasets in assessing bacterial adaptation to IQ-143, a synthetic analog of the novel type N,C-coupled naphthyl-isoquinoline alkaloid ancisheynine. Results: Metabolite measurements, gene expression data and functional assays were combined with metabolic modeling to assess the effects of IQ-143 on Staphylococcus aureus, Staphylococcus epidermidis and human cell lines, as a potential paradigm for novel antibiotics. Genome annotation and PCR validation identified novel enzymes in the primary metabolism of staphylococci. Gene expression response analysis and metabolic modeling demonstrated the adaptation of enzymes to IQ-143, including those not affected by significant gene expression changes. At lower concentrations, IQ-143 was bacteriostatic, and at higher concentrations bactericidal, while the analysis suggested that the mode of action was a direct interference in nucleotide and energy metabolism. Experiments in human cell lines supported the conclusions from pathway modeling and found that IQ-143 had low cytotoxicity. Conclusions: The data suggest that IQ-143 is a promising lead compound for antibiotic therapy against staphylococci. The combination of gene expression and metabolite analyses with in silico modeling of metabolite pathways allowed us to study metabolic adaptations in detail and can be used for the evaluation of metabolic effects of other xenobiotics.
The size-dependent exciton dynamics of one-dimensional aggregates of substituted perylene bisimides are studied by ultrafast transient absorption spectroscopy and kinetic Monte-Carlo simulations as a function of the excitation density and the temperature in the range of 25-90 degrees C. For low temperatures, the aggregates can be treated as infinite chains and the dynamics is dominated by diffusion-driven exciton-exciton annihilation. With increasing temperature the aggregates dissociate into small fragments consisting of very few monomers. This scenario is also supported by the time-dependent anisotropy deduced from polarization-dependent experiments.
A new flavanone-chromone biflavonoid, preussianone (1), has been isolated from the leaves of Garcinia preussii, along with four known biflavonoids. The absolute stereostructures were elucidated by chemical, spectroscopic, and chiroptical methods. The biological properties of the new biflavonoid against several bacterial strains were evaluated.
Background It is well known that carbohydrates play fundamental roles in cell signaling and infection processes as well as tumor formation and progression. However, the interaction pathways and cellular receptors targeted by carbohydrates and glycoconjugates remain poorly examined and understood. This lack of research stems, at least to a major part, from accessibility problems of large, branched oligosaccharides. Results To test glycan - cell interactions in vitro, a variety of tailored oligosaccharides was synthesized chemo-enzymatically. Glycosyltransferases from the GRAS organisms Bacillus megaterium (SacB) and Aspergillus niger (Suc1) were used in this study. Substrate engineering of these glycosyltransferases generally acting on sucrose leads to the controlled formation of novel tailored di-, tri- and tetrasaccharides. Already industrially used as prebiotics in functional food, the immunogenic potential of novel oligosaccharides was characterized in this study. A differential secretion of CXCL8 and CCL2 was observed upon oligosaccharide co-cultivation with colorectal epithelial Caco-2 cells. Conclusion Pure carbohydrates are able to stimulate a cytokine response in human endothelial cells in vitro. The type and amount of cytokine secretion depends on the type of co-cultivated oligosaccharide.
Microbial studies of the Mediterranean sponge Tethya aurantium led to the isolation of the fungus Bartalinia robillardoides strain LF550. The strain produced a number of secondary metabolites belonging to the chloroazaphilones. This is the first report on the isolation of chloroazaphilones of a fungal strain belonging to the genus Bartalinia. Besides some known compounds (helicusin A (1) and deacetylsclerotiorin (2)), three new chloroazaphilones (helicusin E (3); isochromophilone X (4) and isochromophilone XI (5)) and one new pentaketide (bartanolide (6)) were isolated. The structure elucidations were based on spectroscopic analyses. All isolated compounds revealed different biological activity spectra against a test panel of four bacteria: three fungi; two tumor cell lines and two enzymes.
Self-organization and self-sorting processes are responsible for the regulation and control of the vast majority of biological processes that eventually sustain life on our planet. Attempts to unveil the complexity of these systems have been devoted to the investigation of the binding processes between artificial molecules, complexes or aggregates within multicomponent mixtures, which has facilitated the emergence of the field of self-sorting in the last decade. Since, artificial systems involving discrete supramolecular structures, extended supramolecular aggregates or gel-phase materials in organic solvents or—to a lesser extent—in water have been investigated. In this review, we have collected diverse strategies employed in recent years to construct extended supramolecular aggregates in water upon self-sorting of small synthetic molecules. We have made particular emphasis on co-assembly processes in binary mixtures leading to supramolecular structures of remarkable complexity and the influence of different external variables such as solvent and concentration to direct recognition or discrimination processes between these species. The comprehension of such recognition phenomena will be crucial for the organization and evolution of complex matter.
Coherent two-dimensional electronic spectroscopy in the Soret band of a chiral porphyrin dimer
(2013)
Using coherent two-dimensional (2D) electronic spectroscopy in fully noncollinear geometry, we observe the excitonic coupling of β,β'-linked bis[tetraphenylporphyrinato-zinc(II)] on an ultrafast timescale in the excited state. The results for two states in the Soret band originating from an excitonic splitting are explained by population transfer with approximately 100 fs from the energetically higher to the lower excitonic state. This interpretation is consistent with exemplary calculations of 2D spectra for a model four-level system with coupling.
Decandrinin (1), an unprecedented \(C_9\)-spiro-fused 7,8-\(seco-ent\)-abietane, was obtained from the bark of an Indian mangrove, \(Ceriops\ decandra\), collected in the estuary of Godavari, Andhra Pradesh. The constitution and the relative configuration of 1 were determined by HRMS (ESI) and extensive NMR investigations, and the absolute configuration by circular dichroism (CD) and optical-rotatory dispersion (ORD) spectroscopy in combination with quantum-chemical calculations. Decandrinin is the first 7,8-\(seco-ent\)-abietane.
Eight streptophenazines (A-H) have been identified so far as products of Streptomyces strain HB202, which was isolated from the sponge Halichondria panicea from the Baltic Sea. The variation of bioactivities based on small structural changes initiated further studies on new derivatives. Three new streptophenazines (I-K) were identified after fermentation in the present study. In addition, revised molecular structures of streptophenazines C, D, F and H are proposed. Streptophenazines G and K exhibited moderate antibacterial activity against the facultative pathogenic bacterium Staphylococcus epidermidis and against Bacillus subtilis. All tested compounds (streptophenazines G, I-K) also showed moderate activities against PDE 4B.
Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (\(\beta\)-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (\(\alpha\)-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\alpha\)-phase) and up to 3.5 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\beta\)-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on \(\beta\)-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\). The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.
Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with pi-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π-π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process.
New synthetic methodologies for the formation of block copolymers have revolutionized polymer science within the last two decades. However, the formation of supramolecular block copolymers composed of alternating sequences of larger block segments has not been realized yet. Here we show by transmission electron microscopy (TEM), 2D NMR and optical spectroscopy that two different perylene bisimide dyes bearing either a flat (A) or a twisted (B) core self-assemble in water into supramolecular block copolymers with an alternating sequence of (A\(_{m}\)BB)\(_{n}\). The highly defined ultralong nanowire structure of these supramolecular copolymers is entirely different from those formed upon self-assembly of the individual counterparts, that is, stiff nanorods (A) and irregular nanoworms (B), respectively. Our studies further reveal that the as-formed supramolecular block copolymer constitutes a kinetic self-assembly product that transforms into thermodynamically more stable self-sorted homopolymers upon heating.
β-glucans are well-known modulators of the immune system in mammals but little is known about β-glucan triggered immunity in planta. Here we show by isothermal titration calorimetry, circular dichroism spectroscopy and nuclear magnetic resonance spectroscopy that the FGB1 gene from the root endophyte Piriformospora indica encodes for a secreted fungal-specific β-glucan-binding lectin with dual function. This lectin has the potential to both alter fungal cell wall composition and properties, and to efficiently suppress β-glucan-triggered immunity in different plant hosts, such as Arabidopsis, barley and Nicotiana benthamiana. Our results hint at the existence of fungal effectors that deregulate innate sensing of β-glucan in plants.
Multimetallic complexes with extended and highly conjugated bis-2,2':6',2''-terpyridyl bridging ligands, which present building blocks for coordination polymers, are investigated with respect to their ability to act as light-harvesting antennae. The investigated species combine Ru(II)- with Os(II)- and Fe(II)-terpyridyl chromophores, the latter acting as energy sinks. Due to the extended conjugated system the ligands are able to prolong the lifetime of the \(^3\)MLCT states compared to unsubstituted terpyridyl species by delocalization and energetic stabilization of the \(^3\)MLCT states. This concept is applied for the first time to Fe(II) terpyridyl species and results in an exceptionally long lifetime of 23 ps for the Fe(II) \(^3\)MLCT state. While partial energy (>80%) transfer is observed between the Ru(II) and Fe(II) centers with a time-constant of 15 ps, excitation energy is transferred completely from the Ru(II) to the Os(II) center within the first 200 fs after excitation.
A donor-acceptor-donor (D-A-D) type naphthalene-diimide (NDI-H) chromophore exhibits highly cooperative J-aggregation leading to nanotubular self-assembly and gelation in n-decane, as demonstrated by UV/Vis, FT-IR, photoluminescence and microscopy studies. Analysis of temperature-dependent UV/Vis spectra using the nucleation-elongation model and FT-IR data reveals the molecular origin of the cooperative nature of the self-assembly. The supramolecular polymerization is initiated by H-bonding up to a degree of polymerization similar to 20-25, which in a subsequent elongation step promotes J-aggregation in orthogonal direction leading to possibly a sheet-like structure that eventually produces nanotubes. Time-resolved fluorescence and absorption measurements demonstrate that such a tubular assembly enables very effective delocalization of excited states resulting in a remarkably prolonged excited state lifetime.
The aim is to evaluate the effect of modifying poly[(L-lactide)-co-(epsilon-caprolactone)] scaffolds (PLCL) with nanodiamonds (nDP) or with nDP+physisorbed BMP-2 (nDP+BMP-2) on in vivo host tissue response and degradation. The scaffolds are implanted subcutaneously in Balb/c mice and retrieved after 1, 8, and 27 weeks. Molecular weight analysis shows that modified scaffolds degrade faster than the unmodified. Gene analysis at week 1 shows highest expression of proinflammatory markers around nDP scaffolds; although the presence of inflammatory cells and foreign body giant cells is more prominent around the PLCL. Tissue regeneration markers are highly expressed in the nDP+BMP-2 scaffolds at week 8. A fibrous capsule is detectable by week 8, thinnest around nDP scaffolds and at week 27 thickest around PLCL scaffolds. mRNA levels of ALP, COL1 alpha 2, and ANGPT1 are signifi cantly upregulating in the nDP+BMP-2 scaffolds at week 1 with ectopic bone seen at week 8. Even when almost 90% of the scaffold is degraded at week 27, nDP are observable at implantation areas without adverse effects. In conclusion, modifying PLCL scaffolds with nDP does not aggravate the host response and physisorbed BMP-2 delivery attenuates infl ammation while lowering the dose of BMP-2 to a relatively safe and economical level.
The linear and nonlinear optical properties of a series of oligomeric squaraine dyes were investigated by one-photon absorption spectroscopy (1PA) and two-photon absorption (2PA) induced fluorescence spectroscopy. The superchromophores are based on two indolenine squaraine dyes with transoid (SQA) and cisoid configuration (SQB). Using these monomers, linear dimers and trimers as well as star-shaped trimers and hexamers with benzene or triphenylamine cores were synthesised and investigated. The red-shifted and intensified 1PA spectra of all superchromophores could well be explained by exciton coupling theory. In the linear chromophore arrangements we also found superradiance of fluorescence but not in the branched systems. Furthermore, the 2PA showed enhanced cross sections for the linear oligomers but only additivity for the branched systems. This emphasizes that the enhancement of the 2PA cross section in the linear arrangements is probably caused by orbital interactions of higher excited configurations.
Cofacial positioning of two perylene bisimide (PBI) chromophores at a distance of 6.5 angstrom in a cyclophane structure prohibits the otherwise common excimer formation and directs photoexcited singlet state relaxation towards intramolecular symmetry-breaking charge separation (τ\(_{CS}\) = 161 +/- 4 ps) in polar CH\(_2\)Cl\(_2\), which is thermodynamically favored with a Gibbs free energy of ΔG\(_{CS}\) = -0.32 eV. The charges then recombine slowly in τ\(_{CR}\) = 8.90 +/- 0.06 ns to form the PBI triplet excited state, which can be used subsequently to generate singlet oxygen in 27% quantum yield. This sequence of events is eliminated by dissolving the PBI cyclophane in non-polar toluene, where only excited singlet state decay occurs. In contrast, complexation of electron-rich aromatic hydrocarbons by the host PBI cyclophane followed by photoexcitation of PBI results in ultrafast electron transfer (<10 ps) from the guest to the PBI in CH\(_2\)Cl\(_2\). The rate constants for charge separation and recombination increase as the guest molecules become easier to oxidize, demonstrating that charge separation occurs close to the peak of the Marcus curve and the recombination lies far into the Marcus inverted region.
The quantum efficiency of light emission is a crucial parameter of supramolecular aggregates that can be tuned by the molecular design of the monomeric species. Here, we report on a strong variation of the fluorescence quantum yield due to different phases of aggregation for the case of a perylene bisimide dye. In particular, a change of the dominant aggregation character from H- to J-type within the first aggregation steps is found, explaining the observed dramatic change in quantum yield. This behaviour is rationalised by means of a systematic study of the intermolecular potential energy surfaces using the time-dependent density functional based tight-binding (TD-DFTB) method. This provides a correlation between structural changes and a coupling strength and supports the notion of H- type stacked dimers and J-type stack-slipped dimers. The exciton-vibrational level structure is modelled by means of an excitonic dimer model including two effective vibrational modes per monomer. Calculated absorption and fluorescence spectra are found to be in reasonable agreement with experimental ones, thus supporting the conclusion on the aggregation behaviour.