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

G. A. PINO*; I. ALATA; C. DEDONDER-LARDEUX; C. JOUVET; K. SAKOTA; H. SEKIYA

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2011 vol. 13 p. 6325 - 6331

1463-9076

Picoseconds pump and probe experiment has been applied to study the excited state dynamics of 7-azaindole-water 1:2 and 1:3 clusters [7AI(H2O)2,3] in the gas phase.  The vibration-mode selective Excited-State-Triple-Proton Transfer (ESTPT) in 7AI(H2O)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 s(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(H2O)3 measured by nanosecond laser pulses,  the vibronic bands with an energy higher than 200 cm-1 above the origin of the S1 state become very weak.  In contrast, the vibronic bands in the same region emerge in the (1+1?) REMPI spectrum of 7AI(H2O)3 with picoseconds pulses. The decay times drastically decreases when increasing the vibrational energy above 200 cm-1.  Ab-initio calculations show that a second stable ?cyclic- nonplanar isomer? exists in addition to ?bridged-planar isomer?, and that an isomerization from bridged-planar isomer to cyclic-nonplanar isomer is most probably responsible for the short lifetimes of the vibronic states of 7AI(H2O)3.