Simulation methods for liquid-phase molecular spectroscopy based on Franck-Condon factors

SU Hang; LI Maining; LIU Yuhui

doi:10.3969/j.issn.1673-0569.2025.03.003

Abstract：Excited-state proton transfer(ESPT),a fundamental photochemical reaction,plays a crucial role in numerous photochemical and photobiological processes.Its significant practical value in applications like fluorescent probes and organic light-emitting diodes(OLEDs)has attracted growing research attention in recent decades.The characteristic spectroscopic signature of ESPT is dual fluorescence in emission spectra,exhibiting distinct"normal"and"anomalous"bands corresponding to the excited-state reactant and product,respectively.Despite extensive studies through diverse experimental and theoretical methods,conventional quantum chemical approaches relying solely on vertical excitation energies for spectral simulation are demonstrated to be inadequate for elucidating complex photochemical reaction mechanisms.Consequently,methods simulating vibrationally resolved electronic spectra based on Franck-Condon factors are increasingly employed for investigating such mechanisms and the luminescence of novel materials.However,challenges in solution-phase Franck-Condon simulations have restricted the reporting of vibrationally resolved spectra in this context.To overcome this limitation,we recently introduced damped Franck-Condon factors within the mass-weighted Cartesian coordinate framework.This methodology models solute-solvent interactions and interprets solvent enhanced absorption and fluorescence.Implementing these solution-phase Franck-Condon simulations to ESPT reactions yields deeper mechanistic insights,enabling us to propose novel mechanistic perspectives on several ESPT reaction mechanisms from the viewpoint of electronic spectral simulation.