Photoinduced Ultrafast Intramolecular Excited-State Energy Transfer in the Silylene-Bridged Biphenyl and Stilbene (SBS) System: A Nonadiabatic Dynamics Point of View

Abstract

The photoinduced intramolecular excited-state energy-transfer (EET) process in conjugated polymers has received a great deal of research interest because of its important role in the light harvesting and energy transport of organic photovoltaic materials in photoelectric devices. In this work, the silylene-bridged biphenyl and stilbene (SBS) system was chosen as a simplified model system to obtain physical insight into the photoinduced intramolecular energy transfer between the different building units of the SBS copolymer. In the SBS system, the vinylbiphenyl and vinylstilbene moieties serve as the donor (D) unit and the acceptor (A) unit, respectively. The ultrafast excited-state dynamics of the SBS system was investigated from the point of view of nonadiabatic dynamics with the surface-hopping method at the TDDFT level. The first two excited states (S1 and S2) are characterized by local excitations at the acceptor (vinylstilbene) and donor (vinylbiphenyl) units, respectively. Ultrafast S2-S1 decay is responsible for the intramolecular D-A excitonic energy transfer. The geometric distortion of the D moiety play an essential role in this EET process, whereas the A moiety remains unchanged during the nonadiabatic dynamics simulation. The present work provides a direct dynamical approach to understand the ultrafast intramolecular energy-transfer dynamics in SBS copolymers and other similar organic photovoltaic copolymers.

Non-adiabatic Excited-State Molecular Dynamics: Theory and Applications for Modeling Photophysics in Extended Molecular Materials

“…Rates based on the energy gap between states and the total kinetic energy have been proposed by Truhlar et al and implemented by Granucci et al − These energy-based decoherence correction (EDC) and/or coherent switching with decay of mixing (CSDM) methods, have the benefit of being more easily calculated, and are the most widely used decoherence corrections. Often, the parameter suggested by Granucci et al is used regardless of the system being studied. ,,,− While simulations using EDC and CSDM performed on models and small molecular systems lead to results that are relatively independent of the predefined set of decoherence time and parameters, this was shown not to be true when applying the methods to large conjugated molecular systems. Results obtained in simulations of non-radiative relaxation in two conjugated oligomer systems, poly­(phenylene-vinylene) (PPV) and poly­(phenylene-ethynylene) (PPE), have shown a drastic dependence on which parameters are used .…”

C–N Bond Rotation Controls Photoinduced Electron Transfer in an Aminostyrene–Stilbene Donor–Acceptor System

“…In contrast to previous theoretical studies that put the focus on the vertical excitation properties and couplings of the molecular chromophores, we will explore the full excited-state potential energy surfaces (PES) of the DA-Me dimer system in order to fully elucidate the photophysical dynamics. We propose that this dynamical perspective is crucial in order to reach a general understanding of the complex energy transfer and photoinduced electron transfer dynamics in molecular DA systems, as has been demonstrated in various theoretical studies. − Especially, it is well known that the C–N bond rotation in the aminostyrene could lead to a twisted intramolecular charge transfer (TICT) state, and we believe this TICT formation dynamics should not be overlooked. We will pay extra attention to investigate the effects of the C–N bond rotation on the photophysics of DA-Me .…”

(De)localization dynamics of molecular excitons: comparison of mixed quantum-classical and fully quantum treatments

“…15,16 The advantages of the surface hopping simulations are relatively low computational cost (especially when combined with fast electronic structure methods) and ability to treat explicitly (though classically) all nuclear DoFs for relatively large molecular systems. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] However, in order to account for the quantum nature of nuclei and properly describe decoherence the quantum dynamical treatment is needed. 12,14,[33][34][35][36][37] To judge the extent of the spatial exciton (de)localization, in the SH simulations the electronic quantities (transition density matrices, molecular orbitals, particle and hole charges, etc.)…”