TDDFT Study On The Excited State Proton Transfer Reaction

Density functional theory(DFT) and time-dependent density functional theory(TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer(ESIPT) reaction on 8-hydroxyquinoline(8HQ) molecular and 2-(2′-hydroxyphenyl) benzothiazole(HBT) molecular. The main works are presented as follows:1、The geometric structure、absorption spectra、emission spectra、infrared spectra and the excited-state proton transfer potential energy curves of 8HQ in both the ground and the lowest singlet excited states have been calculated by DFT and TDDFT methods 、B3LYP hybrid exchange functional and TZVP basis set, and we also discuss the photo-physical and photo-chemical processes for 8HQ in the excited state. In view of the solvent effect, dichloromethane is used as solvent throughout. The study indicates:(1) The intramolecular hydrogen bond(HB) in 8HQ would be significantly strengthened in the excited state compare with ground state. The ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond(O-H…N).(2) It can decrease the energy gap between the excited state(S1) and ground state(S0) after ultrafast ESIPT process. Thus, the photophysical and photochemical processes of 8HQ can be fully rationalized2 、 The ground state and excited state of HBT are studied by using DFT/B3LYP/TZVP and TDDFT/B3LYP/TZVP theory methods. We discuss whether the product is plane molecular or non-plane molecular in detail. All the geometry optimizations of HBT in the ground and the first excited states are performed in the gas phase. This study indicate:(1) Upon photo-excitation to the excited-state, the calculated potential energy curve is almost flat. As a result, the proton donor can release a proton easily, and the proton accepter can catch the proton without any difficulty.(2) The twisting motion occurs around the central C-C bond after ultrafast ESIPT process by analyzing the twisting potential energy curves. In the end, the IC becomes the main dissipative channel.