Electron-vibrational coupling on the absorption spectrum of dithienyl-diketopyrrolopyrrole dye

摘要

The S-1 <- S-0 electronic spectrum of DPP2T in a chloroform solution was investigated using the vertical gradient (VG) and adiabatic shift (AS) models, which were compared with experimental results. The solvent effects were accounted through the polarizable continuum model (PCM) in non-equilibrium regime. Using the Condon approximation, linear coupling contribution for DPP2T's spectrum is mainly composed of zero-phonon and fundamental transitions. The most intense fundamental transition is related to symmetrical and in-plane normal mode stretching of carbon-carbon bonds belonging pi-conjugated skeleton of DPP2T, which is quinoidized upon S-1 <- S-0 electronic transition. DPP2T's low-frequency torsional modes couple quadratically to the transition. Their thermal excitation at room temperature broadens the spectrum, shifting it slightly to higher energies.