New insight into the potential energy landscape and relaxation pathways of photoexcited aniline from CASSCF and XMCQDPT2 electronic structure calculations

Abstract

There have been a number of recent experimental investigations of the nonadiabatic relaxation dynamics of aniline following excitation to the first three singlet excited states, 1¹ππ*, 1¹π3s/πσ* and 2¹ππ*. Motivated by differences between the interpretations of experimental observations, we have employed CASSCF and XMCQDPT2 calculations to explore the potential energy landscape and relaxation pathways of photoexcited aniline. We find a new prefulvene-like MECI connecting the 1¹ππ* state with the GS in which the carbon-atom carrying the amino group is distorted out-of-plane. This suggests that excitation above the 1¹π3s/πσ* vertical excitation energy could be followed by electronic relaxation from the 1¹ππ* state to the ground-electronic state through this MECI. We find a MECI connecting the 1¹π3s/πσ* and 1¹ππ* states close to the local minimum on 1¹π3s/πσ* which suggests that photoexcitation to the 1¹π3s/πσ* state could be followed by relaxation to the 1¹ππ* state and to the dissociative component of the 1¹π3s/πσ* state. We also find evidence for a new pathway from the 2¹ππ* state to the ground electronic state that is likely to pass through a three-state conical intersection involving the 2¹ππ*, 1¹π3s/πσ* and 1¹ππ* states.