TY - JOUR A1 - Luo, Ying A1 - Utecht, Manuel Martin A1 - Dokic, Jadranka A1 - Korchak, Sergey A1 - Vieth, Hans-Martin A1 - Haag, Rainer A1 - Saalfrank, Peter T1 - Cis-trans isomerisation of substituted aromatic imines a comparative experimental and theoretical study JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - The cis-trans isomerisation of N-benzylideneaniline (NBA) and derivatives containing a central C=N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans (hv) -> cis isomerisation and the kinetics of the thermal backreaction cis (Delta)-> trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition-state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time-dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify "optimal switches" with good photochromicity and reasonable thermal stability. KW - density functional calculations KW - imines KW - isomerization KW - photochemistry KW - thermochemistry Y1 - 2011 U6 - https://doi.org/10.1002/cphc.201100179 SN - 1439-4235 VL - 12 IS - 12 SP - 2311 EP - 2321 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Baranac-Stojanovic, Marija A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Density Functional Calculations of the Anisotropic Effects of Borazine and 1,3,2,4-Diazadiboretidine JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - On the basis of the nucleus-independent chemical shift (NICS) concept, the anisotropic effects of two inorganic rings, namely, borazine and planar 1,3,2,4-diazadiboretidine, are quantitatively calculated and visualized as isochemical shielding surfaces (ICSSs). Dissection of magnetic shielding values along the three Cartesian axes into contributions from s and p bonds by the natural chemical shieldingnatural bond orbital (NCSNBO) method revealed that their appearance is not a simple reflection of the extent of (anti)aromaticity. KW - anisotropic effects KW - aromaticity KW - B,N heterocycles KW - density functional calculations KW - NMR spectroscopy Y1 - 2012 U6 - https://doi.org/10.1002/cphc.201200732 SN - 1439-4235 VL - 13 IS - 17 SP - 3803 EP - 3811 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Goetze, Jan P. A1 - Kröner, Dominik A1 - Banerjee, Shiladitya A1 - Karasulu, Bora A1 - Thiel, Walter T1 - Carotenoids as a shortcut for chlorophyll Soret-to-Q band energy flow JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - It is proposed that xanthophylls, and carotenoids in general, may assist in energy transfer from the chlorophyll Soret band to the Q band. Ground-state (1A(g)) and excited-state (1B(u)) optimizations of violaxanthin (Vx) and zeaxanthin (Zx) are performed in an environment mimicking the light-harvesting complex II (LHCII), including the closest chlorophyll b molecule (Chl). Time-dependent density functional theory (TD-DFT, CAM-B3LYP functional) is used in combination with a semi-empirical description to obtain the excited-state geometries, supported by additional DFT/multireference configuration interaction calculations, with and without point charges representing LHCII. In the ground state, Vx and Zx show similar properties. At the 1B(u) minimum, the energy of the Zx 1Bu state is below the Chl Q band, in contrast to Vx. Both Vx and Zx may act as acceptors of Soret-state energy; transfer to the Q band seems to be favored for Vx. These findings suggest that carotenoids may generally mediate Soret-to-Q energy flow in LHCII. KW - carotenoids KW - chlorophyll KW - density functional calculations KW - energy transfer KW - xanthophylls Y1 - 2014 U6 - https://doi.org/10.1002/cphc.201402233 SN - 1439-4235 SN - 1439-7641 VL - 15 IS - 15 SP - 3391 EP - 3400 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Boese, Adrian Daniel T1 - Density Functional Theory and Hydrogen Bonds: Are We There Yet? JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - Density functional theory (DFT) has become more successful at introducing dispersion interactions, and can be thus applied to a wide range of systems. Amongst these are systems that contain hydrogen bonds, which are extremely important for the biological regime. Here, the description of hydrogen-bonded interactions by DFT with and without dispersion corrections is investigated. For small complexes, for which electrostatics are the determining factor in the intermolecular interactions, the inclusion of dispersion with most functionals yields large errors. Only for larger systems, in which van der Waals interactions are more important, do dispersion corrections improve the performance of DFT for hydrogen-bonded systems. None of the studied functionals, including double hybrid functionals (with the exception of DSD-PBEP86 without dispersion corrections), are more accurate than MP2 for the investigated species. KW - ab initio calculations KW - basis sets KW - density functional calculations KW - hydrogen bonds KW - intermolecular interactions Y1 - 2015 U6 - https://doi.org/10.1002/cphc.201402786 SN - 1439-4235 SN - 1439-7641 VL - 16 IS - 5 SP - 978 EP - 985 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Klaper, Matthias A1 - Linker, Torsten T1 - New Singlet Oxygen Donors Based on Naphthalenes: Synthesis, Physical Chemical Data, and Improved Stability JF - Chemistry - a European journal N2 - Singlet oxygen donors are of current interest for medical applications, but suffer from a short half-life leading to low singlet oxygen yields and problems with storage. We have synthesized more than 25new singlet oxygen donors based on differently substituted naphthalenes in only a few steps. The influence of functional groups on the reaction rate of the photooxygenations, thermolysis, half-life, and singlet oxygen yield has been thoroughly studied. We determined various thermodynamic data and compared them with density functional calculations. Interestingly, remarkable stabilities of functional groups during the photooxygenations and stabilizing effects for some endoperoxides during the thermolysis have been found. Furthermore, we give evidence for a partly concerted and partly stepwise thermolysis mechanism leading to singlet and triplet oxygen, respectively. Our results might be interesting for dark oxygenations and future applications in medicine. KW - density functional calculations KW - oxygenation KW - peroxides KW - photodynamic therapy KW - singlet oxygen Y1 - 2015 U6 - https://doi.org/10.1002/chem.201500146 SN - 0947-6539 SN - 1521-3765 VL - 21 IS - 23 SP - 8569 EP - 8577 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kulesza, Alexander Jan A1 - Titov, Evgenii A1 - Daly, Steven A1 - Wlodarczyk, Radoslaw A1 - Megow, Jörg A1 - Saalfrank, Peter A1 - Choi, Chang Min A1 - MacAleese, Luke A1 - Antoine, Rodolphe A1 - Dugourd, Philippe T1 - Excited States of Xanthene Analogues: Photofragmentation and Calculations by CC2 and Time-Dependent Density Functional Theory JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - Action spectroscopy has emerged as an analytical tool to probe excited states in the gas phase. Although comparison of gas-phase absorption properties with quantum-chemical calculations is, in principle, straightforward, popular methods often fail to describe many molecules of interest-such as xanthene analogues. We, therefore, face their nano-and picosecond laser-induced photofragmentation with excited-state computations by using the CC2 method and time-dependent density functional theory (TDDFT). Whereas the extracted absorption maxima agree with CC2 predictions, the TDDFT excitation energies are blueshifted. Lowering the amount of Hartree-Fock exchange in the DFT functional can reduce this shift but at the cost of changing the nature of the excited state. Additional bandwidth observed in the photofragmentation spectra is rationalized in terms of multiphoton processes. Observed fragmentation from higher-lying excited states conforms to intense excited-to-excited state transitions calculated with CC2. The CC2 method is thus suitable for the comparison with photofragmentation in xanthene analogues. KW - density functional calculations KW - CC2 calculations KW - multiphoton processes KW - photofragmentation KW - xanthenes Y1 - 2016 U6 - https://doi.org/10.1002/cphc.201600650 SN - 1439-4235 SN - 1439-7641 VL - 17 SP - 3129 EP - 3138 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - da Silva, Filipe Ferreira A1 - Varella, Marcio T. do N. A1 - Jones, Nykola C. A1 - Hoffmann, Soren Vronning A1 - Denifl, Stephan A1 - Bald, Ilko A1 - Kopyra, Janina T1 - Electron-Induced Reactions in 3-Bromopyruvic Acid JF - Chemistry - a European journal N2 - 3-Bromopyruvic acid (3BP) is a potential anticancer drug, the action of which on cellular metabolism is not yet entirely clear. The presence of a bromine atom suggests that it is also reactive towards low-energy electrons, which are produced in large quantities during tumour radiation therapy. Detailed knowledge of the interaction of 3BP with secondary electrons is a prerequisite to gain a complete picture of the effects of 3BP in different forms of cancer therapy. Herein, dissociative electron attachment (DEA) to 3BP in the gas phase has been studied both experimentally by using a crossed-beam setup and theoretically through scattering and quantum chemical calculations. These results are complemented by a vacuum ultraviolet absorption spectrum. The main fragmentation channel is the formation of Br- close to 0 eV and within several resonant features at 1.9 and 3-8 eV. At low electron energies, Br- formation proceeds through sigma* and pi* shape resonances, and at higher energies through core-excited resonances. It is found that the electron-capture cross-section is clearly increased compared with that of non-brominated pyruvic acid, but, at the same time, fragmentation reactions through DEA are significantly altered as well. The 3BP transient negative ion is subject to a lower number of fragmentation reactions than those of pyruvic acid, which indicates that 3BP could indeed act by modifying the electron-transport chains within oxidative phosphorylation. It could also act as a radio-sensitiser. KW - density functional calculations KW - dissociative electron attachment KW - drug discovery KW - gas-phase reactions KW - sensitizers Y1 - 2019 U6 - https://doi.org/10.1002/chem.201806132 SN - 0947-6539 SN - 1521-3765 VL - 25 IS - 21 SP - 5498 EP - 5506 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Jay, Raphael Martin A1 - Eckert, Sebastian A1 - Vaz da Cruz, Vinicius A1 - Fondell, Mattis A1 - Mitzner, Rolf A1 - Föhlisch, Alexander T1 - Covalency-driven preservation of local charge densities in a metal-to-ligand charge-transfer excited iron photosensitizer JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - Charge-density rearrangements after metal-to-ligand charge-transfer excitation in an iron photosensitizer are investigated by R. M Jay, A. Fohlisch et al. in their Communication (DOI: 10.1002/anie.201904761). By using time-resolved X-ray absorption spectroscopy, surprising covalency-effects are revealed that inhibit charge-separation at the intra-molecular level. Furthermore, the underlying mechanism is proposed to be generally in effect for all commonly used photosensitizers in light-harvesting applications, which challenges the common perception of electronic charge-transfer. KW - charge-transfer KW - density functional calculations KW - iron KW - photochemistry KW - X-ray absorption spectroscopy Y1 - 2019 U6 - https://doi.org/10.1002/anie.201904761 SN - 1433-7851 SN - 1521-3773 VL - 58 IS - 31 SP - 10742 EP - 10746 PB - Wiley-VCH CY - Weinheim ER -