Mode-selective internal conversion of perylene

Abstract

We observed fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation of jet-cooled perylene-h 12 and perylene-d 12, and carefully examined the vibrational structures of the S0[1] A g and S1[1] B 2u states. We performed vibronic assignments on the basis of the results of ab initio calculation, and found that the vibrational energies in the S1 state are very similar to those in the S0 state, indicating that the potential energy curves are not changed much upon electronic excitation. We conclude that the small structural change is the main cause of its slow radiationless transition and high fluorescence quantum yield at the zero-vibrational level in the S1 state. It has been already reported that the lifetime of perylene is remarkably short at specific vibrational levels in the S1 state. Here, we show that the mode-selective nonradiative process is internal conversion (IC) to the S0 state, and the ν16(a g ) in-plane ring deforming vibration is the promoting (doorway) mode in the S1 state which enhances vibronic coupling with the high-vibrational level (b 2u ) of the S0 state.