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

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, 1(1)pi pi(star), 1(1)pi 3s/pi sigma(star) and 2(1)pi pi(star). 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 1(1)pi pi(star)state with the GS in which the carbon-atom carrying the amino group is distorted out-of-plane. This suggests that excitation above the 1(1)pi 3s/pi sigma(star) vertical excitation energy could be followed by electronic relaxation from the 1(1)pi pi(star) state to the ground-electronic state through this MECI. We find a MECI connecting the 1(1)pi 3s/pi sigma(star) and 1(1)pi pi(star) states close to the local minimum on 1(1)pi 3s/pi sigma(star) which suggests that photoexcitation to the 1(1)pi 3s/pi sigma(star) state could be followed by relaxation to the 1(1)pi pi(star) state and to the dissociative component of the 1(1)pi 3s/pi sigma star state. We also find evidence for a new pathway from the 2(1)pi pi(star) state to the ground electronic state that is likely to pass through a three-state conical intersection involving the 2(1)pi pi(star), 1(1)pi 3s/pi sigma(star) and 1(1)pi pi(star) states.