The investigation of excited state proton transfer mechanism in water-bridged 7-azaindole

Based on the time-dependent density functional theory (TDDFT), the excited-state intermolecular proton transfer (ESIPT) mechanism of water-bridged 7-azaindole has been investigated theoretically. The calculations of primary bond lengths and the IR vibrational spectra between the S-0 state and the S-1 state that verified the intramolecular hydrogen bond were strengthened. The fact that reproduced experimental absorbance and fluorescence emission spectra well theoretically demonstrate that the TDDFT theory we adopted is reasonable and effective. In addition, intramolecular charge transfer based on the frontier molecular orbitals demonstrated the indication of the ESIPT reaction. The constructed potential energy curves of ground state and the first excited state based on keeping the H-2 center dot center dot center dot O-3 and H-6 center dot center dot center dot H-7 distances fixed at a series of values have been used to illustrate the ESIPT process. A relative lower barrier of 5.94 kcal/mol in the S-1 state potential energy curve for type II (lower than that of 9.82 kcal/mol in the S-1 state for type I) demonstrates that type II ESIPT process occurs firstly in 7Al-2H(2)O complex. (C) 2015 Elsevier B.V. All rights reserved.