@unpublished{AuerhammerSchulzSchmiedeletal.2019, author = {Auerhammer, Nina and Schulz, Alexander and Schmiedel, Alexander and Holzapfel, Marco and Hoche, Joscha and R{\"o}hr, Merle I. S. and Mitric, Roland and Lambert, Christoph}, title = {Dynamic exciton localisation in a pyrene-BODIPY-pyrene dye conjugate}, series = {Physical Chemistry Chemical Physics}, journal = {Physical Chemistry Chemical Physics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198718}, year = {2019}, abstract = {The photophysics of a molecular triad consisting of a BODIPY dye and two pyrene chromophores attached in 2-position are investigated by steady state and fs-time resolved transient absorption spectroscopy as well as by field induced surface hopping (FISH) simulations. While the steady state measurements indicate moderate chromophore interactions within the triad, the time resolved measurements show upon pyrene excitation a delocalised excited state which localises onto the BODIPY chromophore with a time constant of 0.12 ps. This could either be interpreted as an internal conversion process within the excitonically coupled chromophores or as an energy transfer from the pyrenes to the BODIPY dye. The analysis of FISH-trajectories reveals an oscillatory behaviour where the excitation hops between the pyrene units and the BODIPY dye several times until finally they become localised on the BODIPY chromophore within 100 fs. This is accompanied by an ultrafast nonradiative relaxation within the excitonic manifold mediated by the nonadiabatic coupling. Averaging over an ensemble of trajectories allowed us to simulate the electronic state population dynamics and determine the time constants for the nonradiative transitions that mediate the ultrafast energy transfer and exciton localisation on BODIPY.}, language = {en} } @unpublished{BoehnkeDellermannCeliketal.2018, author = {B{\"o}hnke, Julian and Dellermann, Theresa and Celik, Mehmet Ali and Krummenacher, Ivo and Dewhurst, Rian D. and Demeshko, Serhiy and Ewing, William C. and Hammond, Kai and Heß, Merlin and Bill, Eckhard and Welz, Eileen and R{\"o}hr, Merle I. S. and Mitric, Roland and Engels, Bernd and Meyer, Franc and Braunschweig, Holger}, title = {Isolation of diradical products of twisted double bonds}, series = {Nature Communications}, journal = {Nature Communications}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160248}, year = {2018}, abstract = {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.}, language = {en} } @unpublished{HumeniukBužančićHocheetal.2020, author = {Humeniuk, Alexander and Bužančić, Margarita and Hoche, Joscha and Cerezo, Javier and Mitric, Roland and Santoro, Fabrizio and Bonačić-Koutecky, Vlasta}, title = {Predicting fluorescence quantum yields for molecules in solution: A critical assessment of the harmonic approximation and the choice of the lineshape function}, series = {The Journal of Chemical Physics}, journal = {The Journal of Chemical Physics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-199305}, year = {2020}, abstract = {For the rational design of new fluorophores, reliable predictions of fluorescence quantum yields from first principles would be of great help. However, efficient computational approaches for predicting transition rates usually assume that the vibrational structure is harmonic. While the harmonic approximation has been used successfully to predict vibrationally resolved spectra and radiative rates, its reliability for non-radiative rates is much more questionable. Since non-adiabatic transitions convert large amounts of electronic energy into vibrational energy, the highly excited final vibrational states deviate greatly from harmonic oscillator eigenfunctions. We employ a time-dependent formalism to compute radiative and non-radiative rates for transitions and study the dependence on model parameters. For several coumarin dyes we compare different adiabatic and vertical harmonic models (AS, ASF, AH, VG, VGF, VH), in order to dissect the importance of displacements, frequency changes and Duschinsky rotations. In addition we analyze the effect of different broadening functions (Gaussian, Lorentzian or Voigt). Moreover, to assess the qualitative influence of anharmonicity on the internal conversion rate, we develop a simplified anharmonic model. We adress the reliability of these models considering the potential errors introduced by the harmonic approximation and the phenomenological width of the broadening function.}, language = {en} } @unpublished{LambertVoelkerKochetal.2015, author = {Lambert, Christoph and V{\"o}lker, Sebastian F. and Koch, Federico and Schmiedel, Alexander and Holzapfel, Marco and Humeniuk, Alexander and R{\"o}hr, Merle I. S. and Mitric, Roland and Brixner, Tobias}, title = {Energy Transfer Between Squaraine Polymer Sections: From helix to zig-zag and All the Way Back}, series = {Journal of the American Chemical Society}, journal = {Journal of the American Chemical Society}, doi = {10.1021/jacs.5b03644}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-159607}, year = {2015}, abstract = {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.}, language = {en} } @unpublished{LindnerSultangaleevaRoehretal.2019, author = {Lindner, Joachim O. and Sultangaleeva, Karina and R{\"o}hr, Merle I. S. and Mitric, Roland}, title = {metaFALCON: A program package for automatic sampling of conical intersection seams using multistate metadynamics}, series = {Journal of Chemical Theory and Computation}, journal = {Journal of Chemical Theory and Computation}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-199258}, year = {2019}, abstract = {The multistate metadynamics for automatic exploration of conical intersection seams and systematic location of minimum energy crossing points in molecular systems and its implementation into the software package metaFALCON is presented. Based on a locally modified energy gap between two Born-Oppenheimer electronic states as a collective variable, multistate metadynamics trajectories are driven toward an intersection point starting from an arbitrary ground state geometry and are subsequently forced to explore the conical intersection seam landscape. For this purpose, an additional collective variable capable of distinguishing structures within the seam needs to be defined and an additional bias is introduced into the off-diagonal elements of an extended (multistate) electronic Hamiltonian. We demonstrate the performance of the algorithm on the examples of the 1,3-butadiene, benzene, and 9H-adenine molecules, where multiple minimum energy crossing points could be systematically located using the Wiener number or Cremer-Pople parameters as collective variables. Finally, with the example of 9H-adenine, we show that the multistate metadynamics potential can be used to obtain a global picture of a conical intersection seam. Our method can be straightforwardly connected with any ab initio or semiempirical electronic structure theory that provides energies and gradients of the respective electronic states and can serve for systematic elucidation of the role of conical intersections in the photophysics and photochemistry of complex molecular systems, thus complementing nonadiabatic dynamics simulations.}, language = {en} } @unpublished{LisinetskayaMitric2019, author = {Lisinetskaya, Polina G. and Mitric, Roland}, title = {Collective Response in DNA-Stabilized Silver Cluster Assemblies from First-Principles Simulations}, series = {The Journal of Physical Chemistry Letters}, journal = {The Journal of Physical Chemistry Letters}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198729}, year = {2019}, abstract = {We investigate fluorescence resonant energy transfer and concurrent electron dynamics in a pair of DNA-stabilized silver clusters. For this purpose we introduce a methodology for the simulation of collective optoelectronic properties of coupled molecular aggregates starting from first-principles quantum chemistry, which can be further applied to a broad range of coupled molecular systems to study their electro-optical response. Our simulations reveal the existence of low-energy coupled excitonic states, which enable ultrafast energy transport between subunits, and give insight into the origin of the fluorescence signal in coupled DNA-stabilized silver clusters, which have been recently experimentally detected. Hence, we demonstrate the possibility of constructing ultrasmall energy transmission lines and optical converters based on these hybrid molecular systems.}, language = {en} } @unpublished{PetersenLindnerMitric2018, author = {Petersen, Jens and Lindner, Joachim O. and Mitric, Roland}, title = {Ultrafast Photodynamics of Glucose}, series = {Journal of Physical Chemistry B}, journal = {Journal of Physical Chemistry B}, doi = {10.1021/acs.jpcb.7b08602}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-159155}, year = {2018}, abstract = {We have investigated the photodynamics of \(\beta\)-D-glucose employing our field-induced surface hopping method (FISH), which allows us to simulate the coupled electron-nuclear dynamics, including explicitly nonadiabatic effects and light-induced excitation. Our results reveal that from the initially populated S\(_{1}\) and S\(_{2}\) states, glucose returns nonradiatively to the ground state within about 200 fs. This takes place mainly via conical intersections (CIs) whose geometries in most cases involve the elongation of a single O-H bond, while in some instances ring-opening due to dissociation of a C-O bond is observed. Experimentally, excitation to a distinct excited electronic state is improbable due to the presence of a dense manifold of states bearing similar oscillator strengths. Our FISH simulations explicitly including a UV laser pulse of 6.43 eV photon energy reveals that after initial excitation the population is almost equally spread over several close-lying electronic states. This is followed by a fast nonradiative decay on the time scale of 100-200 fs, with the final return to the ground state proceeding via the S\(_{1}\) state through the same types of CIs as observed in the field-free simulations.}, language = {en} } @unpublished{RoederHumeniukGiegerichetal.2017, author = {R{\"o}der, Anja and Humeniuk, Alexander and Giegerich, Jens and Fischer, Ingo and Poisson, Lionel and Mitric, Roland}, title = {Femtosecond Time-Resolved Photoelectron Spectroscopy of the Benzyl Radical}, series = {Physical Chemistry Chemical Physics}, journal = {Physical Chemistry Chemical Physics}, doi = {10.1039/C7CP01437F}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-159474}, year = {2017}, abstract = {We present a joint experimental and computational study of the nonradiative deactivation of the benzyl radical, C\(_7\)H\(_7\) after UV excitation. Femtosecond time-resolved photoelectron imaging was applied to investigate the photodynamics of the radical. The experiments were accompanied by excited state dynamics simulations using surface hopping. Benzyl has been excited at 265 nm into the D-band (\(\pi\pi^*\)) and the dynamics was probed using probe wavelengths of 398 nm or 798 nm. With 398 nm probe a single time constant of around 70-80 fs was observed. When the dynamics was probed at 798 nm, a second time constant \(\tau_2\)=1.5 ps was visible. It is assigned to further non-radiative deactivation to the lower-lying D\(_1\)/D\(_2\) states.}, language = {en} } @unpublished{RoederPetersenIssleretal.2019, author = {R{\"o}der, Anja and Petersen, Jens and Issler, Kevin and Fischer, Ingo and Mitric, Roland and Poisson, Lionel}, title = {Exploring the Excited-State Dynamics of Hydrocarbon Radicals, Biradicals and Carbenes using Time-Resolved Photoelectron Spectroscopy and Field-Induced Surface Hopping Simulations}, series = {The Journal of Physical Chemistry A}, journal = {The Journal of Physical Chemistry A}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198734}, year = {2019}, abstract = {Reactive hydrocarbon molecules like radicals, biradicals and carbenes are not only key players in combustion processes and interstellar and atmospheric chemistry, but some of them are also important intermediates in organic synthesis. These systems typically possess many low-lying, strongly coupled electronic states. After light absorption, this leads to rich photodynamics characterized by a complex interplay of nuclear and electronic motion, which is still not comprehensively understood and not easy to investigate both experimentally and theoretically. In order to elucidate trends and contribute to a more general understanding, we here review our recent work on excited-state dynamics of open-shell hydrocarbon species using time-resolved photoelectron spectroscopy and field-induced surface hopping simulations, and report new results on the excited-state dynamics of the tropyl and the 1-methylallyl radical. The different dynamics are compared, and the difficulties and future directions of time-resolved photoelectron spectroscopy and excited state dynamics simulations of open-shell hydrocarbon molecules are discussed.}, language = {en} } @unpublished{TitovHumeniukMitric2020, author = {Titov, Evgenii and Humeniuk, Alexander and Mitric, Roland}, title = {Comparison of moving and fixed basis sets for nonadiabatic quantum dynamics at conical intersections}, series = {Chemical Physics}, journal = {Chemical Physics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-199225}, year = {2020}, abstract = {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 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.}, language = {en} } @unpublished{TitovHumeniukMitric2018, author = {Titov, Evgenii and Humeniuk, Alexander and Mitric, Roland}, title = {Exciton localization in excited-state dynamics of a tetracene trimer: A surface hopping LC-TDDFTB study}, series = {Physical Chemistry Chemical Physics}, journal = {Physical Chemistry Chemical Physics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198680}, year = {2018}, abstract = {Excitons in the molecular aggregates of chromophores are key participants in important processes such as photosynthesis or the functioning of organic photovoltaic devices. Therefore, the exploration of exciton dynamics is crucial. Here we report on exciton localization during excited-state dynamics of the recently synthesized tetracene trimer [Liu et al., Org. Lett., 2017, 19, 580]. We employ the surface hopping approach to nonadiabatic molecular dynamics in conjunction with the long-range corrected time-dependent density functional tight binding (LC-TDDFTB) method [Humeniuk and Mitrić, Comput. Phys. Commun., 2017, 221, 174]. Utilizing a set of descriptors based on the transition density matrix, we perform comprehensive analysis of exciton dynamics. The obtained results reveal an ultrafast exciton localization to a single tetracene unit of the trimer during excited-state dynamics, along with exciton transfer between units.}, language = {en} } @unpublished{TitovHumeniukMitric2020, author = {Titov, Evgenii and Humeniuk, Alexander and Mitric, Roland}, title = {Comparison of moving and fixed basis sets for nonadiabatic quantum dynamics at conical intersections}, series = {Chemical Physics}, journal = {Chemical Physics}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198699}, year = {2020}, abstract = {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.}, language = {en} } @unpublished{WohlgemuthMitric2020, author = {Wohlgemuth, Matthias and Mitric, Roland}, title = {Excitation energy transport in DNA modelled by multi-chromophoric field-induced surface hopping}, series = {Physical Chemistry Chemical Physics}, journal = {Physical Chemistry Chemical Physics}, edition = {submitted version}, doi = {10.1039/D0CP02255A}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-209467}, year = {2020}, abstract = {Absorption of ultraviolet light is known as a major source of carcinogenic mutations of DNA. The underlying processes of excitation energy dissipation are yet not fully understood. In this work we provide a new and generally applicable route for studying the excitation energy transport in multi-chromophoric complexes at an atomistic level. The surface-hopping approach in the frame of the extended Frenkel exciton model combined with QM/MM techniques allowed us to simulate the photodynamics of the alternating (dAdT)10 : (dAdT)10 double-stranded DNA. In accordance with recent experiments, we find that the excited state decay is multiexponential, involving a long and a short component which are due to two distinct mechanisms: formation of long-lived delocalized excitonic and charge transfer states vs. ultrafast decaying localized states resembling those of the bare nucleobases. Our simulations explain all stages of the ultrafast photodynamics including initial photoexcitation, dynamical evolution out of the Franck-Condon region, excimer formation and nonradiative relaxation to the ground state.}, language = {en} }