Photoinduced Symmetry-Breaking Charge Separation Dynamics of Perylene Diimide Dimers: A Nonadiabatic Dynamics Simulation

Abstract

In this work, we systematically investigate the photoinduced dynamics of two perylene diimide (PDI) dimers exhibiting symmetry breaking, namely ${\rm PDI}$-${\rm CH}_3$ and PDI-iso, in both the gas phase and dichloromethane (DCM) with the combination of the optimally tuned screened range-separated hybrid (OT-SRSH) functional, the polarizable continuum model (PCM) and linear-response time-dependent density functional theory (LR-TDDFT) based nonadiabatic molecular dynamics (NAMD) simulations. The results demonstrate that both substituent effects and solvent effects influence the excited-state properties and dynamic processes of symmetry-broken PDI dimers significantly. In the gas phase, ${\rm PDI}$-${\rm CH}_3$ exhibits negligible electron or hole transfer, whereas PDI-iso undergoes photoinduced energy transfer (PEnT). In DCM, the solvent effect not only reduces the excited-state energies of both structures but also alters their photoinduced dynamics by regulating the orders of different types of excitons. In short, ${\rm PDI}$-${\rm CH}_3$ exhibits a photoinduced hole transfer (PHT)-dominated mechanism, while PDI-iso shifts from photoinduced energy transfer (PEnT) to concurrent hole transfer (PHT) and electron transfer (PET), facilitating the charge separation process. Moreover, this work indicates that introducing small substituents, i.e., methyl groups, at the bay positions of PDI to disrupt symmetry can also effectively modulate its photoinduced processes, providing a theoretical foundation for designing novel high-performance optoelectronic devices.