TY  - JOUR
A1  - Meza-Chincha, Ana-Lucia
A1  - Lindner, Joachim O.
A1  - Schindler, Dorothee
A1  - Schmidt, David
A1  - Krause, Ana-Maria
A1  - Röhr, Merle I. S.
A1  - Mitrić, Roland
A1  - Würthner, Frank
T1  - Impact of substituents on molecular properties and catalytic activities of trinuclear Ru macrocycles in water oxidation
N2  - Herein we report a broad series of new trinuclear supramolecular Ru(bda) macrocycles bearing different substituents at the axial or equatorial ligands which enabled investigation of substituent effects on the catalytic activities in chemical and photocatalytic water oxidation. Our detailed investigations revealed that the activities of these functionalized macrocycles in water oxidation are significantly affected by the position at which the substituents were introduced. Interestingly, this effect could not be explained based on the redox properties of the catalysts since these are not markedly influenced by the functionalization of the ligands. Instead, detailed investigations by X-ray crystal structure analysis and theoretical simulations showed that conformational changes imparted by the substituents are responsible for the variation of catalytic activities of the Ru macrocycles. For the first time, macrocyclic structure of this class of water oxidation catalysts is unequivocally confirmed and experimental indication for a hydrogen-bonded water network present in the cavity of the macrocycles is provided by crystal structure analysis. We ascribe the high catalytic efficiency of our Ru(bda) macrocycles to cooperative proton abstractions facilitated by such a network of preorganized water molecules in their cavity, which is reminiscent of catalytic activities of enzymes at active sites.
KW  - water oxidation
KW  - self-assembly
KW  - solar fuels
KW  - supramolecular materials
KW  - catalysis
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-204653
UR  - https://doi.org/10.1039/D0SC01097A
SN  - 2041-6539
ER  - 
TY  - JOUR
A1  - Hoche, Joscha
A1  - Schulz, Alexander
A1  - Dietrich, Lysanne Monika
A1  - Humeniuk, Alexander
A1  - Stolte, Matthias
A1  - Schmidt, David
A1  - Brixner, Tobias
A1  - Würthner, Frank
A1  - Mitric, Roland
T1  - The origin of the solvent dependence of fluorescence quantum yields in dipolar merocyanine dyes
JF  - Chemical Science
N2  - Fluorophores with high quantum yields are desired for a variety of applications. Optimization of promising chromophores requires an understanding of the non-radiative decay channels that compete with the emission of photons. We synthesized a new derivative of the famous laser dye 4-dicyanomethylen-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM),i.e., merocyanine 4-(dicyanomethylene)-2-tert-butyl-6-[3-(3-butyl-benzothiazol-2-ylidene)1-propenyl]-4H-pyran   (DCBT).   We   measured fluorescence lifetimes and quantum yields in a variety of solvents and found a trend opposite to the energy gap law.This motivated a theoretical investigation into the possible non-radiative decay channels. We propose that a barrier to a conical intersection exists that is very sensitive to the solvent polarity. The conical intersection is characterized by a twisted geometry which allows a subsequent photoisomerization. Transient absorption measurements confirmed the formation of a photoisomer in unpolar solvents, while the measurements of fluorescence quantum yields at low temperature demonstrated the existence of an activation energy barrier.
KW  - solvent-dependent fluorescence yield
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198707
UR  - https://doi.org/10.1039/C9SC05012D
VL  - 10
ER  - 
TY  - JOUR
A1  - Hoche, Joscha
A1  - Flock, Marco
A1  - Miao, Xincheng
A1  - Philipp, Luca Nils
A1  - Wenzel, Michael
A1  - Fischer, Ingo
A1  - Mitric, Roland
T1  - Excimer formation dynamics in the isolated tetracene dimer
JF  - Chemical Science
N2  - The understanding of excimer formation and its interplay with the singlet-correlated triplet pair state \(^{1}\)(TT) is of high significance for the development of efficient organic electronics. Here, we study the photoinduced dynamics of the tetracene dimer in the gas phase by time-resolved photoionisation and photoion imaging experiments as well as nonadiabatic dynamics simulations in order to obtain mechanistic insight into the excimer formation dynamics. The experiments are performed using a picosecond laser system for excitation into the S\(_{2}\) state and reveal a biexponential time dependence. The time constants, obtained as a function of excess energy, lie in the range between ≈10 ps and 100 ps and are assigned to the relaxation of the excimer on the S\(_{1}\) surface and to its deactivation to the ground state. Simulations of the quantum-classical photodynamics are carried out in the frame of the semi-empirical CISD and TD-lc-DFTB methods. Both theoretical approaches reveal a dominating relaxation pathway that is characterised by the formation of a perfectly stacked excimer. TD-lc-DFTB simulations have also uncovered a second relaxation channel into a less stable dimer conformation in the S\(_{1}\) state. Both methods have consistently shown that the electronic and geometric relaxation to the excimer state is completed in less than 10 ps. The inclusion of doubly excited states in the CISD dynamics and their diabatisation further allowed to observe a transient population of the \(^{1}\)(TT) state, which, however, gets depopulated on a timescale of 8 ps, leading finally to the trapping in the excimer minimum.
KW  - excimer formation
KW  - tetracene dimer
KW  - organic electronics
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-251559
VL  - 12
IS  - 36
SP  - 11965
EP  - 11975
ER  - 
TY  - JOUR
A1  - Böhnke, Julian
A1  - Dellermann, Theresa
A1  - Celik, Mehmet Ali
A1  - Krummenacher, Ivo
A1  - Dewhurst, Rian D.
A1  - Demeshko, Serhiy
A1  - Ewing, William C.
A1  - Hammond, Kai
A1  - Heß, Merlin
A1  - Bill, Eckhard
A1  - Welz, Eileen
A1  - Röhr, Merle I. S.
A1  - Mitric, Roland
A1  - Engels, Bernd
A1  - Meyer, Franc
A1  - Braunschweig, Holger
T1  - Isolation of diborenes and their 90°-twisted diradical congeners
JF  - Nature Communications
N2  - Molecules containing multiple bonds between atoms—most often in the form of olefins—are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound.
KW  - chemical bonding
KW  - diradicals
KW  - organometallic chemistry
KW  - diborenes
KW  - carbenes
KW  - boron
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-160431
VL  - 9
IS  - Article number: 1197
ER  - 
TY  - JOUR
A1  - Muessig, Jonas H.
A1  - Lisinetskaya, Polina
A1  - Dewhurst, Rian D.
A1  - Bertermann, Rüdiger
A1  - Thaler, Melanie
A1  - Mitric, Roland
A1  - Braunschweig, Holger
T1  - Dibortetraiodid (B\(_2\)I\(_4\)) ist im Festkörper ein Polymer aus sp3‐hybridisiertem Bor
JF  - Angewandte Chemie
N2  - Anhand der ersten Festkörperstrukturen von Dibortetraiodid (B\(_2\)I\(_4\)) wird gezeigt, dass dieses nicht, wie lange angenommen, analog zu den leichteren Dibortetrahalogeniden B\(_2\)F\(_4\), B\(_2\)Cl\(_4\) und B\(_2\)Br\(_4\) in allen Aggregatzuständen in Form diskreter Moleküle mit planaren, dreifach koordinierten Boratomen vorliegt. Röntgenstrukturanalysen, Festkörper‐NMR‐ und IR‐Messungen zeigen, dass B\(_2\)I\(_4\) im Festkörper in zwei polymeren Konformeren vorkommt, die tetraedrisch koordinierte Boratome enthalten. Anhand von DFT‐Rechnungen werden die IR‐Spektren in Lösung und im Festkörper simuliert und mit den experimentellen Daten verglichen.
KW  - Bor
KW  - Diboran
KW  - DFT-Rechnungen
KW  - Festkörperstrukturen
KW  - Halogene
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-219653
VL  - 132
IS  - 14
ER  - 
TY  - JOUR
A1  - Muessig, Jonas H.
A1  - Lisinetskaya, Polina
A1  - Dewhurst, Rian D.
A1  - Bertermann, Rüdiger
A1  - Thaler, Melanie
A1  - Mitric, Roland
A1  - Braunschweig, Holger
T1  - Tetraiododiborane(4) (B\(_2\)I\(_4\)) is a Polymer based on sp\(^3\) Boron in the Solid State
JF  - Angewandte Chemie International Edition
N2  - Herein we present the first solid‐state structures of tetraiododiborane(4) (B\(_2\)I\(_4\)), which was long believed to exist in all phases as discrete molecules with planar, tricoordinate boron atoms, like the lighter tetrahalodiboranes(4) B\(_2\)F\(_4\), B\(_2\)Cl\(_4\), and B\(_2\)Br\(_4\). Single‐crystal X‐ray diffraction, solid‐state NMR, and IR measurements indicate that B\(_2\)I\(_4\) in fact exists as two different polymeric forms in the solid state, both of which feature boron atoms in tetrahedral environments. DFT calculations are used to simulate the IR spectra of the solution and solid‐state structures, and these are compared with the experimental spectra.
KW  - boron tetraiodide
KW  - boron
KW  - density functional theory
KW  - diborane
KW  - halides
KW  - solid-state sturcture
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-209428
VL  - 59
ER  - 
TY  - INPR
A1  - Titov, Evgenii
A1  - Humeniuk, Alexander
A1  - Mitric, Roland
T1  - Comparison of moving and fixed basis sets for nonadiabatic quantum dynamics at conical intersections
T2  - Chemical Physics
N2  - We assess the performance of two different types of basis sets for nonadiabatic quantum dynamics at conical intersections. The basis sets of both types are generated using Ehrenfest trajectories of nuclear coherent states. These trajectories can either serve as a moving (time-dependent) basis or be employed to sample a fixed (time-independent) basis. We demonstrate on the example of two-state two-dimensional and three-state five-dimensional models that both basis set types can yield highly accurate results for population transfer at intersections, as compared with reference quantum dynamics. The details of wave packet evolutions are discussed for the case of the two-dimensional model. The fixed basis is found to be superior to the moving one in reproducing true nonlocal spreading and maintaining correct shape of the wave packet upon time evolution. Moreover, for the models considered, the fixed basis set outperforms the moving one in terms of computational efficiency.
KW  - Nonadiabatic quantum dynamics
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198699
UR  - https://doi.org/10.1016/j.chemphys.2019.110526
N1  - Accepted manuscript
ER  - 
TY  - JOUR
A1  - Turkin, Arthur
A1  - Holzapfel, Marco
A1  - Agarwal, Mohit
A1  - Fischermeier, David
A1  - Mitric, Roland
A1  - Schweins, Ralf
A1  - Gröhns, Franziska
A1  - Lambert, Christoph
T1  - Solvent Induced Helix Folding of Defined Indolenine Squaraine Oligomers
JF  - Chemistry—A European Journal
N2  - 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.
KW  - UV/Vis spectroscopy
KW  - dye chemistry
KW  - solvent effects
KW  - superstructure
KW  - supramolecular folding
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256869
VL  - 27
IS  - 32
ER  - 
TY  - JOUR
A1  - Hirsch, Florian
A1  - Pachner, Kai
A1  - Fischer, Ingo
A1  - Issler, Kevin
A1  - Petersen, Jens
A1  - Mitric, Roland
A1  - Bakels, Sjors
A1  - Rijs, Anouk M.
T1  - Do Xylylenes Isomerize in Pyrolysis?
JF  - ChemPhysChem
N2  - We report infrared spectra of xylylene isomers in the gas phase, using free electron laser (FEL) radiation. All xylylenes were generated by flash pyrolysis. The IR spectra were obtained by monitoring the ion dip signal, using a IR/UV double resonance scheme. A gas phase IR spectrum of para‐xylylene  was recorded, whereas ortho‐ and meta‐xylylene were found to partially rearrange to benzocyclobutene and styrene. Computations of the UV oscillator strength  for all molecules were carried out and provde an explanation for the observation of the isomerization products.
KW  - biradicals
KW  - high-temperature chemistry
KW  - IR spectroscopy
KW  - pyrolysis
KW  - xylylene
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218316
VL  - 21
IS  - 14
SP  - 1515
EP  - 1518
ER  -