Electronic structure calculations and nonadiabatic dynamics simulations of excited-state relaxation of Pigment Yellow 101

Abstract

Pigment Yellow 101 (PY101) is widely used as a typical pigment due to its excellent excited-state properties. However, the origin of its photostability is still elusive. In this work, we have systematically investigated the photodynamics of PY101 by performing combined electronic structure calculations and trajectory-based nonadiabatic dynamics simulations. On the basis of the results, we have found that upon photoexcitation to the S₁ state, PY101 undergoes an essentially barrierless excited-state intramolecular single proton transfer generating an S₁ keto species. In the keto region, there is an energetically accessible S₁/S₀ conical intersection that funnels the system to the S₀ state quickly. In the S₀ state, the keto species either goes back to its trans-enol species through a ground-state reverse hydrogen transfer or arrives at the cis-keto region. In addition, we have found an additional excited-state decay channel for the S₁ enol species, which is directly linked to an S₁/S₀ conical intersection located in the enol region. This mechanism has also been confirmed by our dynamics simulations, in which about 54% of the trajectories decay to the S₀ state via the enol S₁/S₀ conical intersection; while the remaining ones employ the keto S₁/S₀ conical intersection. The gained mechanistic information helps us understand the photostability of the PY101 chromophore and its variants with the same molecular scaffold.