Browsing by Author "Wang, Shi-Ming"

Now showing 1 - 2 of 2

A TDDFT study on the excited-state double proton transfer reaction of 8-hydroxyquinoline along a hydrogen-bonded bridge
(2017-08-21)
Liu, Yu-Hui
;
Wang, Shi-Ming
;
Zhu, Chaoyuan
;
Lin, Sheng Hsien
;
應用化學系
The mechanism of the excited-state double proton transfer (ESDPT) reactions of 8-hydroxyquinoline (8HQ) along three types of hydrogen-bonded bridges-ammonia (NH3), water (H2O) and acetic acid (AcOH) has been investigated by using time-dependent density functional theory. Based on the analysis of hydrogen bond strengths and the excited-state potential energy surfaces (PES) along the proton transfer coordinates, it is concluded that the hydrogen bonds play the key role in the excited-state multiple proton transfer reaction. Moreover, three different concerted mechanisms have been found in 8HQ center dot NH3, 8HQ center dot H2O and 8HQ center dot AcOH complexes. Upon photoexcitation, the deprotonation of a hydroxyl group in 8HQ would occur first in 8HQ center dot NH3 due to the stronger hydrogen bond -OH center dot center dot center dot NH3. On the contrary, the hydrogen bond -OH center dot center dot center dot O-C-OH is much weaker in the 8HQ center dot AcOH complex, and this leads to a fast protonation of -N- in the 8HQ moiety. For the 8HQ center dot H2O complex, the hydrogen bond strengths are almost the same, so that both protons would transfer simultaneously in a symmetrical and concerted fashion.
Orientation hydrogen-bonding effect on vibronic spectra of isoquinoline in water solvent: Franck-Condon simulation and interpretation
(2016-10-28)
Liu, Yu-Hui
;
Wang, Shi-Ming
;
Wang, Chen-Wen
;
Zhu, Chaoyuan
;
Han, Ke-Li
The excited-state orientation hydrogen-bonding dynamics, and vibronic spectra of isoquinoline (IQ) and its cationic form IQc in water have been investigated at the time-dependent density functional theory quantum chemistry level plus Franck-Condon simulation and interpretation. The excited-state orientation hydrogen bond strengthening has been found in IQ: H2O complex due to the charge redistribution upon excitation; this is interpreted by simulated 1: 1 mixed absorption spectra of free IQ and IQ: H2O complex having best agreement with experimental results. Conversely, the orientation hydrogen bond in IQc: H2O complex would be strongly weakening in the S-1 state and this is interpreted by simulated absorption spectra of free IQc having best agreement with experimental results. By performing Franck-Condon simulation, it reveals that several important vibrational normal modes with frequencies about 1250 cm(-1) involving the wagging motion of the hydrogen atoms are very sensitive to the formation of the orientation hydrogen bond for the IQ/IQc:H2O complex and this is confirmed by damped Franck-Condon simulation with free IQ/IQc in water. However, the emission spectra of the IQ and IQc in water have been found differently. Upon the excitation, the simulated fluorescence of IQ in water is dominated by the IQ: H2O complex; thus hydrogen bond between IQ and H2O is much easier to form in the S-1 state. While the weakened hydrogen bond in IQc: H2O complex is probably cleaved upon the laser pulse because the simulated emission spectrum of the free IQc is in better agreement with the experimental results. Published by AIP Publishing.