Communication: Mode-dependent excited-state lifetime of phenol under the S-1/S(2 )conical intersection

Abstract

Phenol can serve as a model for examining the deactivation of the aromatic amino acid tyrosine following UV excitation, which mainly occurs through a repulsive pi sigma* state along the O-H bond. The reaction barrier formed by the conical intersection between the optically bright S-1 (pi pi*) state and the dissociative S-2 (pi sigma*) state does not inhibit O-H bond rupture even though the excitation energy is below the barrier height. To examine the O-H bond-rupture dynamics in association with the initial excited vibrational modes, we used a picosecond laser to investigate the vibrational-mode-dependent excited-state lifetime of phenol under the S-1/S-2 conical intersection. Unexpectedly short lifetimes were observed in the S-1 state for a '' symmetric vibrational modes (including nu(4), nu(16a), tau OH, and nu(5)). These results clarify recent theoretical calculations showing that the relaxation from S-1 to S-2 either occurs via symmetry-allowed non-adiabatic transitions or is topographically linked to a lower energy minimum on the multidimensional potential energy surface. Published by AIP Publishing.