TY - JOUR A1 - Megow, Jörg A1 - Kulesza, Alexander A1 - May, Volkhard T1 - A mixed quantum-classical description of pheophorbide a linear absorption spectra: Quantum-corrections of the Q(y)- and Q(x)-absorption vibrational satellites JF - Chemical physics letters N2 - The ground-state classical path approximation is utilized to compute molecular absorption spectra in a mixed quantum-classical frame. To improve the description for high-frequency vibrational satellites, related quantum correction factors are introduced. The improved method is demonstrated for the Q(y),and Q(x)-bands of pheophorbide a. (C) 2015 Elsevier B.V. All rights reserved. Y1 - 2016 U6 - https://doi.org/10.1016/j.cplett.2015.11.016 SN - 0009-2614 SN - 1873-4448 VL - 643 SP - 61 EP - 65 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Megow, Jörg A1 - Körzdörfer, Thomas A1 - Renger, Thomas A1 - Sparenberg, Mino A1 - Blumstengel, Sylke A1 - Henneberger, Fritz A1 - May, Volkhard T1 - Calculating Optical Absorption Spectra of Thin Polycrystalline Organic Films: Structural Disorder and Site-Dependent van der Waals Interaction JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - We propose a new approach for calculating the change of the absorption spectrum of a molecule when moved from the gas phase to a crystalline morphology. The so-called gas-to-crystal shift Delta epsilon(m) is mainly caused by dispersion effects and depends sensitively on the molecules specific position in the nanoscopic setting. Using an extended dipole approximation, we are able to divide Delta epsilon(m)= -QW(m) in two factors, where Q depends only on the molecular species and accounts for all nonresonant electronic transitions contributing to the dispersion while W-m is a geometry factor expressing the site dependence of the shift in a given molecular structure. The ability of our approach to predict absorption spectra is demonstrated using the example of polycrystalline films of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI). Y1 - 2015 U6 - https://doi.org/10.1021/acs.jpcc.5b01587 SN - 1932-7447 VL - 119 IS - 10 SP - 5747 EP - 5751 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Plehn, Thomas A1 - Megow, Jörg A1 - May, Volkhard T1 - Concerted charge and energy transfer processes in a highly flexible fullerene-dye system: a mixed quantum-classical study JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Photoinduced excitation energy transfer and accompanying charge separation are elucidated for a supramolecular system of a single fullerene covalently linked to six pyropheophorbide-a dye molecules. Molecular dynamics simulations are performed to gain an atomistic picture of the architecture and the surrounding solvent. Excitation energy transfer among the dye molecules and electron transfer from the excited dyes to the fullerene are described by a mixed quantum-classical version of the Forster rate and the semiclassical Marcus rate, respectively. The mean characteristic time of energy redistribution lies in the range of 10 ps, while electron transfer proceeds within 150 ps. In between, on a 20 to 50 ps time-scale, conformational changes take place in the system. This temporal hierarchy of processes guarantees efficient charge separation, if the structure is exposed to a solvent. The fast energy transfer can adopt the dye excitation to the actual conformation. In this sense, the probability to achieve charge separation is large enough since any dominance of unfavorable conformations that exhibit a large dye-fullerene distance is circumvented. And the slow electron transfer may realize an averaging with respect to different conformations. To confirm the reliability of our computations, ensemble measurements on the charge separation dynamics are simulated and a very good agreement with the experimental data is obtained. Y1 - 2014 U6 - https://doi.org/10.1039/c4cp01081g SN - 1463-9076 SN - 1463-9084 VL - 16 IS - 25 SP - 12949 EP - 12958 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Plehn, Thomas A1 - Megow, Jörg A1 - May, Volkhard T1 - Concerted charge and energy transfer processes in a highly flexible fullerene–dye system BT - a mixed quantum–classical study N2 - Photoinduced excitation energy transfer and accompanying charge separation are elucidated for a supramolecular system of a single fullerene covalently linked to six pyropheophorbide-a dye molecules. Molecular dynamics simulations are performed to gain an atomistic picture of the architecture and the surrounding solvent. Excitation energy transfer among the dye molecules and electron transfer from the excited dyes to the fullerene are described by a mixed quantum–classical version of the Förster rate and the semiclassical Marcus rate, respectively. The mean characteristic time of energy redistribution lies in the range of 10 ps, while electron transfer proceeds within 150 ps. In between, on a 20 to 50 ps time-scale, conformational changes take place in the system. This temporal hierarchy of processes guarantees efficient charge separation, if the structure is exposed to a solvent. The fast energy transfer can adopt the dye excitation to the actual conformation. In this sense, the probability to achieve charge separation is large enough since any dominance of unfavorable conformations that exhibit a large dye–fullerene distance is circumvented. And the slow electron transfer may realize an averaging with respect to different conformations. To confirm the reliability of our computations, ensemble measurements on the charge separation dynamics are simulated and a very good agreement with the experimental data is obtained. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 279 Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-98791 ER - TY - JOUR A1 - Plehn, Thomas A1 - Ziemann, Dirk A1 - Megow, Jörg A1 - May, Volkhard T1 - Frenkel to Wannier-Mott Exciton Transition: Calculation of FRET Rates for a Tubular Dye Aggregate Coupled to a CdSe Nanocrystal JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - The coupling is investigated of Frenkel-like exciton states formed in a tubular dye aggregate (TDA) to Wannier-Mott-like excitations of a semiconductor nanocrystal (NC). A double well TDA of the cyanine dye C8S3 with a length of 63.4 nm and a diameter of 14.7 nm is considered. The TDA interacts with a spherical Cd819Te630 NC of 4.5 nm diameter. Electronic excitations of the latter are described in a tight-binding model of the electrons and holes combined with a configuration interaction scheme to consider their mutual Coulomb coupling. To achieve a proper description of TDA excitons, a recently determined structure has been used, the energy transfer coupling has been defined as a screened interaction of atomic centered transition charges, and the site energies of the dye molecules have been the subject of a polarization correction. Even if both nanoparticles are in direct contact, the energy transfer coupling between the exciton levels of the TDA and of the NC stays below 1 meV. It results in FRET-type energy transfer with rates somewhat larger than 10(9)/s. They coincide rather well with recent preliminary experiments. Y1 - 2015 U6 - https://doi.org/10.1021/jp5111696 SN - 1520-6106 VL - 119 IS - 24 SP - 7467 EP - 7472 PB - American Chemical Society CY - Washington ER - TY - INPR A1 - Megow, Jörg A1 - Körzdörfer, Thomas A1 - Renger, Thomas A1 - Sparenberg, Mino A1 - Blumstengel, Sylke A1 - May, Volkhard T1 - Reply to "Comment on 'Calculating Optical Absorption Spectra of Thin Polycrystalline Organic Films: Structural Disorder and Site-Dependent van der Waals Interaction" T2 - The journal of physical chemistry : C, Nanomaterials and interfaces Y1 - 2015 U6 - https://doi.org/10.1021/acs.jpcc.5b05536 SN - 1932-7447 VL - 119 IS - 32 SP - 18818 EP - 18820 PB - American Chemical Society CY - Washington ER - TY - GEN A1 - Megow, Jörg A1 - Röhr, Merle I. S. A1 - Schmidt am Busch, Marcel A1 - Renger, Thomas A1 - Mitrić, Roland A1 - Kirstein, Stefan A1 - Rabe, Jürgen P. A1 - May, Volkhard T1 - Site-dependence of van der Waals interaction explains exciton spectra of double-walled tubular J-aggregates N2 - The simulation of the optical properties of supramolecular aggregates requires the development of methods, which are able to treat a large number of coupled chromophores interacting with the environment. Since it is currently not possible to treat large systems by quantum chemistry, the Frenkel exciton model is a valuable alternative. In this work we show how the Frenkel exciton model can be extended in order to explain the excitonic spectra of a specific double-walled tubular dye aggregate explicitly taking into account dispersive energy shifts of ground and excited states due to van der Waals interaction with all surrounding molecules. The experimentally observed splitting is well explained by the site-dependent energy shift of molecules placed at the inner or outer side of the double-walled tube, respectively. Therefore we can conclude that inclusion of the site-dependent dispersive effect in the theoretical description of optical properties of nanoscaled dye aggregates is mandatory. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 191 Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-79978 SP - 6741 EP - 6747 ER - TY - JOUR A1 - Megow, Jörg A1 - Röhr, Merle I. S. A1 - Schmidt am Busch, Marcel A1 - Renger, Thomas A1 - Mitrić, Roland A1 - Kirstein, Stefan A1 - Rabe, Jürgen P. A1 - May, Volkhard T1 - Site-dependence of van der Waals interaction explains exciton spectra of double-walled tubular J-aggregates JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies N2 - The simulation of the optical properties of supramolecular aggregates requires the development of methods, which are able to treat a large number of coupled chromophores interacting with the environment. Since it is currently not possible to treat large systems by quantum chemistry, the Frenkel exciton model is a valuable alternative. In this work we show how the Frenkel exciton model can be extended in order to explain the excitonic spectra of a specific double-walled tubular dye aggregate explicitly taking into account dispersive energy shifts of ground and excited states due to van der Waals interaction with all surrounding molecules. The experimentally observed splitting is well explained by the site-dependent energy shift of molecules placed at the inner or outer side of the double-walled tube, respectively. Therefore we can conclude that inclusion of the site-dependent dispersive effect in the theoretical description of optical properties of nanoscaled dye aggregates is mandatory. Y1 - 2015 U6 - https://doi.org/10.1039/c4cp05945j SN - 1463-9084 SN - 1463-9076 VL - 17 IS - 10 SP - 6741 EP - 6747 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Megow, Jörg A1 - Röhr, Merle I. S. A1 - Busch, Marcel A1 - Renger, Thomas A1 - Mitric, Roland A1 - Kirstein, Stefan A1 - Rabe, Jürgen P. A1 - May, Volkhard T1 - Site-dependence of van der Waals interaction explains exciton spectra of double-walled tubular J-aggregates JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - The simulation of the optical properties of supramolecular aggregates requires the development of methods, which are able to treat a large number of coupled chromophores interacting with the environment. Since it is currently not possible to treat large systems by quantum chemistry, the Frenkel exciton model is a valuable alternative. In this work we show how the Frenkel exciton model can be extended in order to explain the excitonic spectra of a specific double-walled tubular dye aggregate explicitly taking into account dispersive energy shifts of ground and excited states due to van der Waals interaction with all surrounding molecules. The experimentally observed splitting is well explained by the site-dependent energy shift of molecules placed at the inner or outer side of the double-walled tube, respectively. Therefore we can conclude that inclusion of the site-dependent dispersive effect in the theoretical description of optical properties of nanoscaled dye aggregates is mandatory. Y1 - 2015 U6 - https://doi.org/10.1039/c4cp05945j SN - 1463-9076 SN - 1463-9084 VL - 17 IS - 10 SP - 6741 EP - 6747 PB - Royal Society of Chemistry CY - Cambridge ER -