Fragment Diabatization Linear Vibronic Coupling Model for Quantum Dynamics of Multichromophoric Systems: Population of the Charge-Transfer State in the Photoexcited Guanine–Cytosine Pair

Abstract

We introduce a method (FrD-LVC) based on a fragment diabatization (FrD) for the parametrization of a Linear Vibronic Coupling (LVC) model suitable for studying the photophysics of multichromophore systems. In combination with effective quantum dynamics (QD) propagations with multilayer multiconfigurational time-dependent Hartree (ML-MCTDH), the FrD-LVC approach gives access to the study of the competition between intra-chromophore decays, like those at conical intersections, and inter-chromophore processes, like exciton localization/delocalization and the involvement of charge transfer (CT) states. We used FrD-LVC parametrized with TD-DFT calculations, adopting either CAM-B3LYP or ωB97X-D functionals, to study the ultrafast photoexcited QD of a Guanine-Cytosine (GC) hydrogen bonded pair, within a Watson-Crick arrangement, considering up to 12 coupled diabatic electronic states and the effect of all the 99 vibrational coordinates. The bright excited states localized on C and, especially, on G are predicted to be strongly coupled to the G->C CT state which is efficiently and quickly populated after an excitation to any of the four lowest energy bright local excited states. Our QD simulations show that more than 80% of the excited population on G and ~50% of that on C decays to this CT state in less than 50 fs. We investigate the role of vibronic effects in the population of the CT state and show it depends mainly on its large reorganization energy so that it can occur even when it is significantly less stable than the bright states in the Franck-Condon region.At the same time, we document that the formation of the GC pair almost suppresses the involvement of dark nπ* excited states in the photoactivated dynamics. File list (2) download file view on ChemRxiv main_FrD-LVC.pdf (2.14 MiB) download file view on ChemRxiv SI_FrD-LVC.pdf (4.59 MiB)

Electronic Circular Dichroism Spectra of DNA Quadruple Helices Studied by Molecular Dynamics Simulations and Excitonic Calculations including Charge Transfer States

“…However, the large size of the GQ systems studied here (containing at least 12 G bases) imposes the use of TD-DFT as reference QM method. The implementation of the FrD technique within the framework of TD-DFT has been presented previously, and we refer readers to these texts for further information [34,38].…”

Surface Hopping Dynamics on Vibronic Coupling Models

“…For these reasons, VC models have been extensively used in combination with the multiconfigurational time-dependent Hartree (MCTDH) method 14−16 for quantum dynamics (QD) studies and to obtain vibronic spectra of moderately sized stiff molecules. 7,9,15,17 In recent years, VC models experienced a renaissance in the field of exciton dynamics 18,19 and in the context of the Frenkel−Holstein vibronic exciton Hamilto-nian. 20 However, MCTDH dynamics with VC potentials still formally scales exponentially, becoming infeasible for large systems.…”

The Ultrafast Quantum Dynamics of Photoexcited Adenine–Thymine Basepair Investigated with a Fragment-based Diabatization and a Linear Vibronic Coupling Model

“…As previously done for DNA nucleobases and G-quadruplexes, ,− , we express the reference states and overlap matrix within the framework of TD-DFT, and further details can be found in these papers. Similarities and differences of our approach with the work of Tamura and Burghardt on conjugated polymers and fullerene systems − have also been analyzed in ref .…”

“…We consider 3 different choices of reference states in order to examine their effect on the LVC model, and resultant dynamics. We set the reference states as equivalent to the adiabatic states of the MC at the reference geometry and label this as the standard LVC (St-LVC) approach. This is a typical choice adopted for LVC models, and we have used this method previously in the study of individual chromophores. ,− We use our recently proposed fragment diabatization (FrD) technique to define the reference states . In this approach, the reference states are the adiabatic states of the isolated fragments of the MC (for LEs), or one electron transitions between orbitals on different fragments (for CT states).…”

“…We use our recently proposed fragment diabatization (FrD) technique to define the reference states . In this approach, the reference states are the adiabatic states of the isolated fragments of the MC (for LEs), or one electron transitions between orbitals on different fragments (for CT states).…”