@article{HeRauchFriedrichetal.2019, author = {He, Jiang and Rauch, Florian and Friedrich, Alexandra and Sieh, Daniel and Ribbeck, Tatjana and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {N-Heterocyclic Olefins as Electron Donors in Combination with Triarylborane Acceptors: Synthesis, Optical and Electronic Properties of D-π-A Compounds}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, doi = {10.1002/chem.201903118}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204690}, pages = {13777-13784}, year = {2019}, abstract = {N-heterocyclic olefins (NHOs), relatives of N-heterocyclic carbenes (NHCs), exhibit high nucleophilicity and soft Lewis basic character. To investigate their π-electron donating ability, NHOs were attached to triarylborane π-acceptors (A) giving donor (D)-π-A compounds 1-3. In addition, an enamine π-donor analogue (4) was synthesized for comparison. UV-visible absorption studies show a larger red shift for the NHO-containing boranes than for the enamine analogue, a relative of cyclic (alkyl)(amino) carbenes (CAACs). Solvent-dependent emission studies indicate that 1-4 have moderate intramolecular charge-transfer (ICT) behavior. Electrochemical investigations reveal that the NHO-containing boranes have extremely low reversible oxidation potentials (e.g., for 3, \(E^{ox}_{1/2}\) =-0.40 V vs. ferrocene/ferrocenium, Fc/Fc\(^+\), in THF). Time-dependent (TD) DFT calculations show that the HOMOs of 1-3 are much more destabilized than that of the enamine-containing 4, which confirms the stronger donating ability of NHOs.}, language = {en} } @article{GriesbeckMichailRauchetal.2019, author = {Griesbeck, Stefanie and Michail, Evripidis and Rauch, Florian and Ogasawara, Hiroaki and Wang, Chenguang and Sato, Yoshikatsu and Edkins, Robert M. and Zhang, Zuolun and Taki, Masayasu and Lambert, Christoph and Yamaguchi, Shigehiro and Marder, Todd B.}, title = {The Effect of Branching on the One- and Two-Photon Absorption, Cell Viability, and Localization of Cationic Triarylborane Chromophores with Dipolar versus Octupolar Charge Distributions for Cellular Imaging}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {57}, doi = {10.1002/chem.201902461}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-212887}, pages = {13164 -- 13175}, year = {2019}, abstract = {Two different chromophores, namely a dipolar and an octupolar system, were prepared and their linear and nonlinear optical properties as well as their bioimaging capabilities were compared. Both contain triphenylamine as the donor and a triarylborane as the acceptor, the latter modified with cationic trimethylammonio groups to provide solubility in aqueous media. The octupolar system exhibits a much higher two-photon brightness, and also better cell viability and enhanced selectivity for lysosomes compared with the dipolar chromophore. Furthermore, both dyes were applied in two-photon excited fluorescence (TPEF) live-cell imaging.}, language = {en} } @article{GriesbeckMichailRauchetal.2019, author = {Griesbeck, Stefanie and Michail, Evripidis and Rauch, Florian and Ogasawara, Hiroaki and Wang, Chenguang and Sato, Yoshikatsu and Edkins, Robert M. and Zhang, Zuolun and Taki, Masayasu and Lambert, Christoph and Yamaguchi, Shigehiro and Marder, Todd B.}, title = {The Effect of Branching on One- and Two-Photon Absorption, Cell Viability and Localization of Cationic Triarylborane Chromophores with Dipolar versus Octupolar Charge Distributions for Cellular Imaging}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {57}, doi = {10.1002/chem.201902461}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204829}, pages = {13164-13175}, year = {2019}, abstract = {Two different chromophores, namely a dipolar and an octupolar system, were prepared and their linear and nonlinear optical properties as well as their bioimaging capabilities were compared. Both contain triphenylamine as the donor and a triarylborane as the acceptor, the latter modified with cationic trimethylammonio groups to provide solubility in aqueous media. The octupolar system exhibits a much higher two-photon brightness, and also better cell viability and enhanced selectivity for lysosomes compared with the dipolar chromophore. Furthermore, both dyes were applied in two-photon excited fluorescence (TPEF) live-cell imaging.}, language = {en} } @article{BelaidiRauchZhangetal.2019, author = {Belaidi, Houmam and Rauch, Florian and Zhang, Zuolun and Latouche, Camille and Boucekkine, Abdou and Marder, Todd B. and Halet, Jean-Francois}, title = {Insights into the optical properties of triarylboranes with strongly electron-accepting bis(fluoromesityl)boryl groups: when theory meets experiment}, series = {ChemPhotoChem}, volume = {4}, journal = {ChemPhotoChem}, number = {3}, doi = {10.1002/cptc.201900256}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-205600}, pages = {173-180}, year = {2019}, abstract = {The photophysical properties (absorption, fluorescence and phosphorescence) of a series of triarylboranes of the form 4-D-C\(_6\)H\(_4\)-B(Ar)\(_2\) (D=\(^t\)Bu or NPh\(_2\); Ar=mesityl (Mes) or 2,4,6-tris(trifluoromethylphenyl (Fmes)) were analyzed theoretically using state-of-the-art DFT and TD-DFT methods. Simulated emission spectra and computed decay rate constants are in very good agreement with the experimental data. Unrestricted electronic computations including vibronic contributions explain the unusual optical behavior of 4-\(^t\)Bu-C\(_6\)H\(_4\)-B(Fmes)\(_2\) 2, which shows both fluorescence and phosphorescence at nearly identical energies (at 77 K in a frozen glass). Analysis of the main normal modes responsible for the phosphorescence vibrational fine structure indicates that the bulky tert-butyl group tethered to the phenyl ring is strongly involved. Interestingly, in THF solvent, the computed energies of the singlet and triplet excited states are very similar for compound 2 only, which may explain why 2 shows phosphorescence in contrast to the other members of the series.}, language = {en} } @article{LenczykRoyNitschetal.2019, author = {Lenczyk, Carsten and Roy, Dipak Kumar and Nitsch, J{\"o}rn and Radacki, Krzysztof and Rauch, Florian and Dewhurst, Rian D. and Bickelhaupt, F. Matthias and Marder, Todd B. and Braunschweig, Holger}, title = {Steric Effects Dictate the Formation of Terminal Arylborylene Complexes of Ruthenium from Dihydroboranes}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {59}, issn = {1521-3765}, doi = {10.1002/chem.201902890}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-219537}, pages = {13566-13571}, year = {2019}, abstract = {The steric and electronic properties of aryl substituents in monoaryl borohydrides (Li[ArBH\(_3\)]) and dihydroboranes were systematically varied and their reactions with [Ru(PCy\(_3\))\(_2\)HCl(H\(_2\))] (Cy: cyclohexyl) were studied, resulting in bis(σ)-borane or terminal borylene complexes of ruthenium. These variations allowed for the investigation of the factors involved in the activation of dihydroboranes in the synthesis of terminal borylene complexes. The complexes were studied by multinuclear NMR spectroscopy, mass spectrometry, X-ray diffraction analysis, and density functional theory (DFT) calculations. The experimental and computational results suggest that the ortho-substitution of the aryl groups is necessary for the formation of terminal borylene complexes.}, language = {en} } @phdthesis{Rauch2020, author = {Rauch, Florian}, title = {1,3-Bis(trifluoromethyl)benzene: A Versatile Building Block for the Synthesis of New Boron-Containing Conjugated Systems}, doi = {10.25972/OPUS-21147}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-211478}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {Chapter 1 Thermally activated delayed fluorescence (TADF) materials provide a strategy to improve external quantum efficiencies of organic light emitting diodes (OLEDs). Because of spin-statistics, 25\% singlet and 75\% triplet excitons are generated in an electronic device. Conventional organic emitters cannot harvest the triplet excitons, due to low spin orbit coupling, and exhibit low external quantum efficiencies. TADF materials have to be designed in such a way, that the energy gap between the lowest singlet and triplet states (ΔES-T) is sufficiently small to allow reverse intersystem crossing (rISC) in organic systems. An established structure property relationship for the generation of TADF materials is the spatial separation of HOMO and LUMO via an orthogonal arrangement of donor and acceptor in donor-π-acceptor (D-π-A) compounds. This is achieved by increasing the steric bulk of the π-bridge. However, this is not always the most efficient method and electronic parameters have to be considered. In a combined experimental and theoretical study, a computational protocol to predict the excited states in D-π-A compounds containing the B(FXyl)2 (FXyl = 2,6-bis(trifluoromethyl)phenyl) acceptor group for the design of new TADF emitters is presented. To this end, the effect of different donor and π-bridge moieties on the energy gaps between local and charge-transfer singlet and triplet states was examined. To prove the computationally aided design concept, the D-π-B(FXyl)2 compounds Cbz-π (1), Cbz-Meπ (2), Phox-Meπ (3), Phox-MeOπ (4), and MeO₃Ph-FMeπ (5) were synthesized and fully characterized. The photophysical properties of these compounds in various solvents, polymeric film and in a frozen matrix were investigated in detail and show excellent agreement with the computationally obtained data (Figure 5.1). A simple structure-property relationship based on the molecular fragment orbitals of the donor and the π-bridge which minimize the relevant singlet-triplet gaps to achieve efficient TADF emitters is presented.   Chapter 2 Three-coordinate boron is widely used as an acceptor in conjugated materials. In recent years the employment of trifluoromethylated aryls was shown to improve the acceptor properties of such boranes. Astonishingly, the use of ortho-trifluoromethylated aryls in boron containing systems also improves the stability of those systems in regard to their inherent reactivity towards nucleophiles. Borafluorenes are stronger acceptors than their non-annulated triarylborane derivatives. In previous studies, the effect of trifluoromethylated aryls as the exo-aryl moieties in borafluorenes, as well as the effect of fluorination on the backbone, were examined. As the latter suffers from a very low stability, systems using trifluoromethyl groups, both on the exo-aryl as well as the borafluorene backbone were designed in order to maximize both the stability as well as the acceptor strength. Three different perfluoroalkylated borafluorenes were prepared and their electronic and photophysical properties were investigated. The systems have four trifluoromethyl moieties on the borafluorene moiety as well as two trifluoromethyl groups at the ortho positions of their exo-aryl moieties. They differ with regard to the para-substituents on their exo-aryl moieties, being a proton (FXylFBf), a trifluoromethyl group (FMesFBf) or a dimethylamino group (p NMe2-FXylFBf), respectively. Furthermore, an acetonitrile adduct of FMesFBf was obtained and characterized. All derivatives exhibit extraordinarily low reduction potentials, comparable to those of perylenediimides. The most electron deficient derivative FMesFBf was also chemically reduced and its radical anion isolated and characterized. Furthermore, the photophysical properties of all compounds were investigated. All compounds exhibit weakly allowed lowest energy absorptions and very long fluorescent lifetimes of ca. 250 ns up to 1.6 μs; however, the underlying mechanisms differ. The donor substituted derivative p-NMe2-FXylFBf exhibits thermally activated delayed fluorescence from a charge transfer (CT) state, while the FMesFBf and FXylFBf borafluorenes exhibit only weakly allowed locally excited (LE) transitions due to their symmetry and low transition dipole moments, as suggested by DFT and TD-DFT calculations.   Chapter 3 Conjugated dendrimers find wide application in various fields, such as charge transport/storage or emitter materials in organic solar cells or OLEDs. Previous studies on boron containing conjugated dendrimers are scarce and mostly employ a convergent synthesis approach, lacking a simple, generally applicable synthetic access. A new divergent approach was designed and conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C-H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF2] or [N(nBu)4][HF2]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators (Figure 5.7). Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. The conjugation does not further increase upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane sub-units, suggesting a potential application as photonic antennas.   Chapter 4 A surprisingly high electronically-driven regioselectivity for the iridium-catalyzed C-H borylation using [Ir(COD)OMe]2 (COD = 1,5-cyclooctadiene) as the precatalytic species, bis(pinacolato)diboron (B2pin2) as the boron source and 4,4'-ditertbutyl-2,2'-bipyridin (dtbpy) as the ligand of D-π-A systems with diphenylamino (1) or carbazolyl (2) moieties as the donor, bis(2,6-bis(trifluoromethyl)phenyl)boryl (B(FXyl)2) as the acceptor, and 1,4-phenylene as the π-bridge was observed. Under these conditions, borylation was observed only at the sterically least encumbered para-positions of the acceptor groups. As boronate esters are versatile building blocks for organic synthesis (C-C coupling, functional group transformations), the C-H borylation represents a simple potential method for post-functionalization by which electronic or other properties of D-π-A systems can be fine-tuned for specific applications. The photophysical and electrochemical properties of the borylated (1-(Bpin)2) and unborylated (1) diphenylamino-substituted D-π-A systems were investigated. Interestingly, the borylated derivative exhibits coordination of THF to the boronate ester moieties, influencing the photophysical properties and exemplifying the non-innocence of boronate esters.}, subject = {Triarylborane}, language = {en} } @article{RauchEndresFriedrichetal.2020, author = {Rauch, Florian and Endres, Peter and Friedrich, Alexandra and Sieh, Daniel and H{\"a}hnel, Martin and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Ji, Lei and Marder, Todd B.}, title = {An Iterative Divergent Approach to Conjugated Starburst Borane Dendrimers}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {57}, doi = {10.1002/chem.202001985}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218345}, pages = {12951 -- 12963}, year = {2020}, abstract = {Using a new divergent approach, conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C-H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF\(_{2}\)] or [N(nBu\(_{4}\))][HF\(_{2}\)]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators. Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. However, the conjugation does not increase further upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane subunits, suggesting a potential application as photonic antennas.}, language = {en} } @article{RauchFuchsFriedrichetal.2020, author = {Rauch, Florian and Fuchs, Sonja and Friedrich, Alexandra and Sieh, Daniel and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {Highly Stable, Readily Reducible, Fluorescent, Trifluoromethylated 9-Borafluorenes}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {56}, doi = {10.1002/chem.201905559}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218390}, pages = {12794 -- 12808}, year = {2020}, abstract = {Three different perfluoroalkylated borafluorenes (\(^{F}\)Bf) were prepared and their electronic and photophysical properties were investigated. The systems have four trifluoromethyl moieties on the borafluorene moiety as well as two trifluoromethyl groups at the ortho positions of their exo-aryl moieties. They differ with regard to the para substituents on their exo-aryl moieties, being a proton \(^{F}\)Xyl\(^{F}\)Bf, \(^{F}\)Xyl: 2,6-bis(trifluoromethyl)phenyl), a trifluoromethyl group (\(^{F}\)Mes\(^{F}\)Bf, \(^{F}\)Mes: 2,4,6-tris(trifluoromethyl)phenyl) or a dimethylamino group (p-NMe\(_{2}\)-\(^{F}\)Xyl\(^{F}\)Bf, p-NMe\(_{2}\)-\(^{F}\)Xyl: 4-(dimethylamino)-2,6-bis(trifluoromethyl)phenyl), respectively. All derivatives exhibit extraordinarily low reduction potentials, comparable to those of perylenediimides. The most electron-deficient derivative \(^{F}\)Mes\(^{F}\)Bf was also chemically reduced and its radical anion isolated and characterized. Furthermore, all compounds exhibit very long fluorescent lifetimes of about 250 ns up to 1.6 μs; however, the underlying mechanisms responsible for this differ. The donor-substituted derivative p-NMe\(_{2}\)-\(^{F}\)Xyl\(^{F}\)Bf exhibits thermally activated delayed fluorescence (TADF) from a charge-transfer (CT) state, whereas the \(^{F}\)Mes\(^{F}\)Bf and FXylFBf borafluorenes exhibit only weakly allowed locally excited (LE) transitions due to their symmetry and low transition-dipole moments.}, language = {en} } @article{FergerBanKrošletal.2021, author = {Ferger, Matthias and Ban, Željka and Krošl, Ivona and Tomić, Sanja and Dietrich, Lena and Lorenzen, Sabine and Rauch, Florian and Sieh, Daniel and Friedrich, Alexandra and Griesbeck, Stefanie and Kenđel, Adriana and Miljanić, Snežana and Piantanida, Ivo and Marder, Todd B.}, title = {Bis(phenylethynyl)arene Linkers in Tetracationic Bis-triarylborane Chromophores Control Fluorimetric and Raman Sensing of Various DNAs and RNAs}, series = {Chemistry-A European Journal}, volume = {27}, journal = {Chemistry-A European Journal}, number = {16}, doi = {10.1002/chem.202005141}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256717}, pages = {5142-5159}, year = {2021}, abstract = {We report four new luminescent tetracationic bis-triarylborane DNA and RNA sensors that show high binding affinities, in several cases even in the nanomolar range. Three of the compounds contain substituted, highly emissive and structurally flexible bis(2,6-dimethylphenyl-4-ethynyl)arene linkers (3: arene=5,5′-2,2′-bithiophene; 4: arene=1,4-benzene; 5: arene=9,10-anthracene) between the two boryl moieties and serve as efficient dual Raman and fluorescence chromophores. The shorter analogue 6 employs 9,10-anthracene as the linker and demonstrates the importance of an adequate linker length with a certain level of flexibility by exhibiting generally lower binding affinities than 3-5. Pronounced aggregation-deaggregation processes are observed in fluorimetric titration experiments with DNA for compounds 3 and 5. Molecular modelling of complexes of 5 with AT-DNA, suggest the minor groove as the dominant binding site for monomeric 5, but demonstrate that dimers of 5 can also be accommodated. Strong SERS responses for 3-5 versus a very weak response for 6, particularly the strong signals from anthracene itself observed for 5 but not for 6, demonstrate the importance of triple bonds for strong Raman activity in molecules of this compound class. The energy of the characteristic stretching vibration of the C≡C bonds is significantly dependent on the aromatic moiety between the triple bonds. The insertion of aromatic moieties between two C≡C bonds thus offers an alternative design for dual Raman and fluorescence chromophores, applicable in multiplex biological Raman imaging.}, language = {en} } @article{HeRauchFriedrichetal.2021, author = {He, Jiang and Rauch, Florian and Friedrich, Alexandra and Krebs, Johannes and Krummenacher, Ivo and Bertermann, R{\"u}diger and Nitsch, J{\"o}rn and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {Phenylpyridyl-fused boroles: a unique coordination mode and weak B-N coordination-induced dual fluorescence}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {9}, doi = {10.1002/anie.202013692}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256423}, pages = {4833-4840}, year = {2021}, abstract = {Phenylpyridyl-fused boroles [TipPBB1]\(_4\) and TipPBB2 were synthesized and their properties investigated. [TipPBB1]\(_4\) forms a tetramer in both the solid state and solution. TipPBB2 contains a 4-coordinate boron atom in the solid state but dissociates to give a 3-coordinate boron species in solution. TipPBB2 shows interesting temperature-dependent dual fluorescence in solution because of the equilibrium between 3- and 4-coordinate boron species due to weak N⋅⋅⋅B intermolecular coordination.}, language = {en} }