Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen OPUS4-34520 unpublished Saal, Fridolin; Swain, Asim; Schmiedel, Alexander; Holzapfel, Marco; Lambert, Christoph; Ravat, Prince Push-Pull [7]Helicene Diimide: Excited-State Charge Transfer and Solvatochromic Circularly Polarised Luminescence In this communication we describe a helically chiral push-pull molecule named 9,10-dimethoxy-[7]helicene diimide, displaying fluorescence (FL) and circularly polarised luminescence (CPL) over nearly the entire visible spectrum dependent on solvent polarity. The synthesised molecule exhibits an unusual solvent polarity dependence of FL quantum yield and nonradiative rate constant, as well as remarkable gabs and glum values along with high configurational stability. submitted version 2023 urn:nbn:de:bvb:20-opus-345207 Institut für Organische Chemie OPUS4-27643 Wissenschaftlicher Artikel Bold, Kevin; Stolte, Matthias; Shoyama, Kazutaka; Krause, Ana-Maria; Schmiedel, Alexander; Holzapfel, Marco; Lambert, Christoph; Würthner, Frank Macrocyclic Donor-Acceptor Dyads Composed of Oligothiophene Half-Cycles and Perylene Bisimides A series of donor-acceptor (D−A) macrocyclic dyads consisting of an electron-poor perylene bisimide (PBI) π-scaffold bridged with electron-rich α-oligothiophenes bearing four, five, six and seven thiophene units between the two phenyl-imide substituents has been synthesized and characterized by steady-state UV/Vis absorption and fluorescence spectroscopy, cyclic and differential pulse voltammetry as well as transient absorption spectroscopy. Tying the oligothiophene strands in a conformationally fixed macrocyclic arrangement leads to a more rigid π-scaffold with vibronic fine structure in the respective absorption spectra. Electrochemical analysis disclosed charged state properties in solution which are strongly dependent on the degree of rigidification within the individual macrocycle. Investigation of the excited state dynamics revealed an oligothiophene bridge size-dependent fast charge transfer process for the macrocyclic dyads upon PBI subunit excitation. 2022 Chemistry – A European Journal 28 30 urn:nbn:de:bvb:20-opus-276435 10.1002/chem.202200355 Institut für Organische Chemie OPUS4-27027 Wissenschaftlicher Artikel Mieczkowski, Mateusz; Steinmetzger, Christian; Bessi, Irene; Lenz, Ann-Kathrin; Schmiedel, Alexander; Holzapfel, Marco; Lambert, Christoph; Pena, Vladimir; Höbartner, Claudia Large Stokes shift fluorescence activation in an RNA aptamer by intermolecular proton transfer to guanine Fluorogenic RNA aptamers are synthetic functional RNAs that specifically bind and activate conditional fluorophores. The Chili RNA aptamer mimics large Stokes shift fluorescent proteins and exhibits high affinity for 3,5-dimethoxy-4-hydroxybenzylidene imidazolone (DMHBI) derivatives to elicit green or red fluorescence emission. Here, we elucidate the structural and mechanistic basis of fluorescence activation by crystallography and time-resolved optical spectroscopy. Two co-crystal structures of the Chili RNA with positively charged DMHBO+ and DMHBI+ ligands revealed a G-quadruplex and a trans-sugar-sugar edge G:G base pair that immobilize the ligand by π-π stacking. A Watson-Crick G:C base pair in the fluorophore binding site establishes a short hydrogen bond between the N7 of guanine and the phenolic OH of the ligand. Ultrafast excited state proton transfer (ESPT) from the neutral chromophore to the RNA was found with a time constant of 130 fs and revealed the mode of action of the large Stokes shift fluorogenic RNA aptamer. 2021 Nature Communications 12 urn:nbn:de:bvb:20-opus-270274 10.1038/s41467-021-23932-0 Institut für Organische Chemie OPUS4-25686 Wissenschaftlicher Artikel Turkin, Arthur; Holzapfel, Marco; Agarwal, Mohit; Fischermeier, David; Mitric, Roland; Schweins, Ralf; Gröhns, Franziska; Lambert, Christoph Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers A protecting group strategy was employed to synthesise a series of indolenine squaraine dye oligomers up to the nonamer. The longer oligomers show a distinct solvent dependence of the absorption spectra, that is, either a strong blue shift or a strong red shift of the lowest energy bands in the near infrared spectral region. This behaviour is explained by exciton coupling theory as being due to H- or J-type coupling of transition moments. The H-type coupling is a consequence of a helix folding in solvents with a small Hansen dispersity index. DOSY NMR, small angle neutron scattering (SANS), quantum chemical and force field calculations agree upon a helix structure with an unusually large pitch and open voids that are filled with solvent molecules, thereby forming a kind of clathrate. The thermodynamic parameters of the folding process were determined by temperature dependent optical absorption spectra. 2021 8380–8389 Chemistry—A European Journal 27 32 urn:nbn:de:bvb:20-opus-256869 10.1002/chem.202101063 Institut für Organische Chemie OPUS4-25656 Wissenschaftlicher Artikel Bold, Kevin; Stolte, Matthias; Shoyama, Kazutaka; Holzapfel, Marco; Schmiedel, Alexander; Lambert, Christoph; Würthner, Frank Macrocyclic donor-acceptor dyads composed of a perylene bisimide dye surrounded by oligothiophene bridges Two macrocyclic architectures comprising oligothiophene strands that connect the imide positions of a perylene bisimide (PBI) dye have been synthesized via a platinum-mediated cross-coupling strategy. The crystal structure of the double bridged PBI reveals all syn-arranged thiophene units that completely enclose the planar PBI chromophore via a 12-membered macrocycle. The target structures were characterized by steady-state UV/Vis absorption, fluorescence and transient absorption spectroscopy, as well as cyclic and differential pulse voltammetry. Both donor-acceptor dyads show ultrafast Förster Resonance Energy Transfer and photoinduced electron transfer, thereby leading to extremely low fluorescence quantum yields even in the lowest polarity cyclohexane solvent. 2022 Angewandte Chemie Internationale Edition 61 1 urn:nbn:de:bvb:20-opus-256569 10.1002/anie.202113598 Institut für Organische Chemie OPUS4-25452 Wissenschaftlicher Artikel Mieczkowski, Mateusz; Steinmetzger, Christian; Bessi, Irene; Lenz, Ann-Kathrin; Schmiedel, Alexander; Holzapfel, Marco; Lambert, Christoph; Pena, Vladimir; Höbartner, Claudia Large Stokes shift fluorescence activation in an RNA aptamer by intermolecular proton transfer to guanine Fluorogenic RNA aptamers are synthetic functional RNAs that specifically bind and activate conditional fluorophores. The Chili RNA aptamer mimics large Stokes shift fluorescent proteins and exhibits high affinity for 3,5-dimethoxy-4-hydroxybenzylidene imidazolone (DMHBI) derivatives to elicit green or red fluorescence emission. Here, we elucidate the structural and mechanistic basis of fluorescence activation by crystallography and time-resolved optical spectroscopy. Two co-crystal structures of the Chili RNA with positively charged DMHBO+ and DMHBI+ ligands revealed a G-quadruplex and a trans-sugar-sugar edge G:G base pair that immobilize the ligand by π-π stacking. A Watson-Crick G:C base pair in the fluorophore binding site establishes a short hydrogen bond between the N7 of guanine and the phenolic OH of the ligand. Ultrafast excited state proton transfer (ESPT) from the neutral chromophore to the RNA was found with a time constant of 130 fs and revealed the mode of action of the large Stokes shift fluorogenic RNA aptamer. 2021 3549 Nature Communications 12 urn:nbn:de:bvb:20-opus-254527 10.1038/s41467-021-23932-0 Institut für Organische Chemie OPUS4-20816 Wissenschaftlicher Artikel Hattori, Yohei; Michail, Evripidis; Schmiedel, Alexander; Moos, Michael; Holzapfel, Marco; Krummenacher, Ivo; Braunschweig, Holger; Müller, Ulrich; Pflaum, Jens; Lambert, Christoph Luminescent Mono-, Di-, and Tri-radicals: Bridging Polychlorinated Triarylmethyl Radicals by Triarylamines and Triarylboranes Up to three polychlorinated pyridyldiphenylmethyl radicals bridged by a triphenylamine carrying electron withdrawing (CN), neutral (Me), or donating (OMe) groups were synthesized and analogous radicals bridged by tris(2,6-dimethylphenyl)borane were prepared for comparison. All compounds were as stable as common closed-shell organic compounds and showed significant fluorescence upon excitation. Electronic, magnetic, absorption, and emission properties were examined in detail, and experimental results were interpreted using DFT calculations. Oxidation potentials, absorption and emission energies could be tuned depending on the electron density of the bridges. The triphenylamine bridges mediated intramolecular weak antiferromagnetic interactions between the radical spins, and the energy difference between the high spin and low spin states was determined by temperature dependent ESR spectroscopy and DFT calculations. The fluorescent properties of all radicals were examined in detail and revealed no difference for high and low spin states which facilitates application of these dyes in two-photon absorption spectroscopy and OLED devices. 2019 15463-15471 Chemistry - A European Journal 25 68 urn:nbn:de:bvb:20-opus-208162 10.1002/chem.201903007 Physikalisches Institut OPUS4-20748 Wissenschaftlicher Artikel Merz, Julia; Dietz, Maximilian; Vonhausen, Yvonne; Wöber, Frederik; Friedrich, Alexandra; Sieh, Daniel; Krummenacher, Ivo; Braunschweig, Holger; Moos, Michael; Holzapfel, Marco; Lambert, Christoph; Marder, Todd B. Synthesis, Photophysical and Electronic Properties of New Red-to-NIR Emitting Donor-Acceptor Pyrene Derivatives We synthesized new pyrene derivatives with strong bis(para -methoxyphenyl)amine donors at the 2,7-positions and n -azaacene acceptors at the K-region of pyrene. The compounds possess a strong intramolecular charge transfer, leading to unusual properties such as emission in the red to NIR region (700 nm), which has not been reported before for monomeric pyrenes. Detailed photophysical studies reveal very long intrinsic lifetimes of >100 ns for the new compounds, which is typical for 2,7-substituted pyrenes but not for K-region substituted pyrenes. The incorporation of strong donors and acceptors leads to very low reduction and oxidation potentials, and spectroelectrochemical studies show that the compounds are on the borderline between localized Robin-Day class-II and delocalized Robin-Day class-III species. 2020 438-453 Chemistry - A European Journal 26 2 urn:nbn:de:bvb:20-opus-207486 10.1002/chem.201904219 Institut für Anorganische Chemie OPUS4-15960 unpublished Lambert, Christoph; Völker, Sebastian F.; Koch, Federico; Schmiedel, Alexander; Holzapfel, Marco; Humeniuk, Alexander; Röhr, Merle I. S.; Mitric, Roland; Brixner, Tobias Energy Transfer Between Squaraine Polymer Sections: From helix to zig-zag and All the Way Back Joint experimental and theoretical study of the absorption spectra of squaraine polymers in solution provide evidence that two different conformations are present in solution: a helix and a zig-zag structure. This unique situation allows investigating ultrafast energy transfer processes between different structural segments within a single polymer chain in solution. The understanding of the underlying dynamics is of fundamental importance for the development of novel materials for light-harvesting and optoelectronic applications. We combine here femtosecond transient absorption spectroscopy with time-resolved 2D electronic spectroscopy showing that ultrafast energy transfer within the squaraine polymer chains proceeds from initially excited helix segments to zig-zag segments or vice versa, depending on the solvent as well as on the excitation wavenumber. These observations contrast other conjugated polymers such as MEH-PPV where much slower intrachain energy transfer was reported. The reason for the very fast energy transfer in squaraine polymers is most likely a close matching of the density of states between donor and acceptor polymer segments because of very small reorganization energy in these cyanine-like chromophores. 2015 Journal of the American Chemical Society urn:nbn:de:bvb:20-opus-159607 10.1021/jacs.5b03644 Institut für Organische Chemie OPUS4-2161 Dissertation Holzapfel, Marco Photoinduced Charge Transfer Processes in Triarylamine Based Redox Cascades In the first part of this work a new approach to measure transient absorption spectra of fluorescent compounds by means of laser flash photolysis technique was presented. Generally, the recorded transient absorption signal consists of transient absorption, fluorescence and ground state bleaching. Thus, for fluorescent chromophores a fluorescence correction is indispensable in order to obtain undisturbed absorption decay curves as well as accurate transient absorption spectra. Due to time response characteristics of the PMT detector the fluorescence contribution cannot be corrected by recording the fluorescence separately. Measuring two transient absorption signals with probe light differing in intensity, compounds with quantum yields up to ~ 35 % can be investigated. This is a major improvement because transient absorption spectroscopy is a powerful method to gain insight into the kinetics and the energy of excited states and information in the time domain of fluorescence are no longer lost. In the second part the synthesis and the photophysical characterisation of redox cascades were reported. These cascades consist of an acridine acceptor and up to three triarylamine donor subunits. The redox potentials of the triarylamines were tuned by adequate substituents in the para-position of the phenyl ring to ensure a directed redox gradient. Upon photoexcitation a locally excited state or a CT state is populated which then injects a hole onto the adjacent donor and consequently results in a CS state. Fluorescence and transient absorption measurements revealed that HT depends strongly on donor strength and solvent polarity. Formation of a CS state was only observed in case of strong terminal donors or polar solvents. A low lying localised triplet state acts as an energy trap and quenches all CS states even in case of the cascade with the strongest terminal donor in very polar solvents. Furthermore, population of a CS state catalyses the formation of this triplet states which results in a shorter lifetime of the CS state compared to the lifetime of the CT state of the corresponding reference compound. Compared to redox cascades already reported in literature, the electronic coupling between the redox centres was decreased by sterical as well as electronic effects. To prolong the lifetime of the CS state saturated spacers on the one hand and a perpendicular orientation of the acceptor and the adjacent donor on the other hand were selected. The twisting of the subunits forming the CT state results in a higher degree of charge separation but its contribution to increase the lifetimes of the CS states is of minor importance. The longer lifetime of the CS states can be ascribed to the saturated spacers. Experimental data in combination with calculated values indicate that charge recombination takes place in the Marcus normal region by a superexchange mechanisms. Although charge recombination of the known cascades is located in the Marcus inverted region, these CS states decay faster than the CS states of the compounds investigated in this work. 2007 urn:nbn:de:bvb:20-opus-25276 Institut für Organische Chemie