Photon induced isomerization in the first excited state of the 7-azaindole-(H2O)3 cluster

• Published in: Physical chemistry chemical physics : PCCP 2011-04, Vol.13 (13), p.6325-6331
• Main Authors: PINO, Gustavo A, ALATA, Ivan, DEDONDER, Claude, JOUVET, Christophe, SAKOTA, Kenji, SEKIYA, Hiroshi
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Indoles - chemistry; Isomerism; Molecular Structure; Photons; Quantum Theory; Water - chemistry
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c1cp00015b

A picosecond pump and probe experiment has been applied to study the excited state dynamics of 7-azaindole-water 1 ∶ 2 and 1 ∶ 3 clusters [7AI(H(2)O)(2,3)] in the gas phase. The vibrational-mode selective Excited-State-Triple-Proton Transfer (ESTPT) in 7AI(H(2)O)(2) proposed from the frequency-resolved study has been confirmed by picosecond decays. The decay times for the vibronic states involving the ESTPT promoting mode σ(1) (850-1000 ps) are much shorter than those for the other vibronic states (2100-4600 ps). In the (1 + 1) REMPI spectrum of 7AI(H(2)O)(3) measured by nanosecond laser pulses, the vibronic bands with an energy higher than 200 cm(-1) above the origin of the S(1) state become very weak. In contrast, the vibronic bands in the same region emerge in the (1 + 1') REMPI spectrum of 7AI(H(2)O)(3) with picosecond pulses. The decay times drastically decrease when increasing the vibrational energy above 200 cm(-1). Ab initio calculations show that a second stable "cyclic-nonplanar isomer" exists in addition to a "bridged-planar isomer", and that an isomerization from a bridged-planar isomer to a cyclic-nonplanar isomer is most probably responsible for the short lifetimes of the vibronic states of 7AI(H(2)O)(3).