Excited state hydrogen transfer dynamics in substituted phenols and their complexes with ammonia: ππ*−πσ* energy gap propensity and ortho-substitution effect.

PINO, G. A.; OLDANI, A. N.; MARCECA, E.; FUJII, M.; ISHIUCHI, S-I.; MIYAZAKI, M.; BROQUIER, M.; DEDONDER, C.; JOUVET, C.

JOURNAL OF CHEMICAL PHYSICS

AMER INST PHYSICS

Año: 2010 p. 245061 - 245068

0021-9606

Lifetimes of the first electronic excited state (S1) of fluorine and methyl (o-, m- and p-) substituted phenols and their complexes with one ammonia molecule have been measured for the 00 transition and for the intermolecular stretching σ1 levels in complexes, using picosecond pump-probe spectroscopy. Excitation energies to the S1 ππ* and S2 πσ* states are obtained by the quantum chemical calculation at the MP2 and CC2 level using the aug-cc-pVDZ basis set for the ground state and the S1 optimized geometries. The observed lifetimes and the energy gaps between the ππ* and πσ* states show a good correlation, the lifetime being shorter for a smaller energy gap. This propensity suggests that the major dynamics in the excited state concerns an excited state hydrogen detachment or transfer (ESHD/T) promoted directly by a S1/S2 conical intersection, rather than via internal conversion to the ground state. A specific shortening of lifetime is found in the o-fluorophenol-ammonia complex and explained in terms of the vibronic coupling between the ππ* and πσ* states occurring through the out-of-plane distortion of the C-F bond.