ABSTRACT
The gas phase structure and excited state dynamics of o-aminophenol-H2O complex have been investigated using REMPI, IR-UV hole-burning spectroscopy, and pump-probe experiments with picoseconds laser pulses. The IR-UV spectroscopy indicates that the isomer responsible for the excitation spectrum corresponds to an orientation of the OH bond away from the NH2 group. The water molecule acts as H-bond acceptor of the OH group of the chromophore. The complexation of o-aminophenol with one water molecule induced an enhancement in the excited state lifetime on the band origin. The variation of the excited state lifetime of the complex with the excess energy from 1.4 ± 0.1 ns for the 0-0 band to 0.24 ± 0.3 ns for the band at 0-0 + 120 cm(-1) is very similar to the variation observed in the phenol-NH3 system. This experimental result suggests that the excited state hydrogen transfer reaction is the dominant channel for the non radiative pathway. Indeed, excited state ab initio calculations demonstrate that H transfer leading to the formation of the H3O(â¢) radical within the complex is the main reactive pathway.
ABSTRACT
The geometries of 1-naphthol-(piperidine)n (1-NpOH-(Pip)n) (n = 0-3) clusters have been calculated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods to investigate excited-state proton transfer (ESPT) in the low-lying singlet excited states, La and Lb. For the n = 1 cluster, no PT structure was found in Lb and La as well as the ground state, S0. For n = 2, optically accessible Lb from S0 shows the PT structure. We therefore concluded that the threshold size of ESPT is n = 2, which is consistent with previous experimental results. ESPT in 1-NpOH-(Pip)n is simply triggered by optical excitation to Lb. It is essentially different from the 1-NpOH-(NH3)n cluster in which an internal conversion process is required to promote ESPT. From the calculated structures, the importance of the solvation of the π-ring is strongly suggested rather than the proton affinity in ESPT.
