We have investigated multiple-proton transfer reactions in the S1 state of hydrated 7-azaindole (7AI) clusters, 7AI(H2O)2 and 7AI(H2O)3, in the gas phase by using electronic and vibrational spectroscpy and time-resolved picosecond spectroscopy. Vibrational-mode selective excited-state-triple-proton transfer (ESTPT) was observed in 7AI(H2O)2 through the measurement of the dispersed fluorescence spectra and resonance-enhanced multiphoton ionization spectra. The vibrational-mode selective ESTPT was confirmed by picosecond decays. The decay times for the vibronic states involving the ESTPT promoting mode s(1) (0.85�1.0 ns) were much shorter than those for the other vibronic states (2.1�4.6 ns). The excited-state dynamics of 7AI(H2O)3 has been found to be very different from that of 7AI(H2O)2. A rearrangement of the hydrogen bond network occurs by exciting the vbironic states in S1; The �bridged planar� structure changes to a �cyclic non-planar� structure by photoexcitation. The excitation of vibronic statesabove 745 cm-1 in S1 induced ESTPT and provided visible emission from a tautomeric form. The existence of the cyclic non-planar structure was supported by comparing the observed and theoretical IR spectra. CAS-PT2 calculation (X.-F. Yu et al. J. Phys. Chem. A 116  , 10566 (2012)) showed that the potential energy barrier for the excited-state quadruple proton transfer (ESQPT) is much higher than that of ESTPT via the cyclic non-planar structure, consistent with the reaction mechanism proposed by our group (G.A. Pino et al. Phys. Chem. Chem. Phys.13 ,6325 (2011)) .

Excited-state multiple proton transfer in hydrated 7-azaindole clusters in the gas phase

248th National Meeting (2014)

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