The Theory Study Of The Hydrogen Bond Effects In Excited State Of Several Organic Molecular Systems In Methanol

Molecular photochemistry is significantly affected by the intermolecular interactions between solute and solvent in solution. As a site-specific local interaction between hydrogen donor and acceptor molecules, intermolecular hydrogen bond plays a fundamental element of molecular systems in solution. For example, the radiationless deactivation via internal conversion (IC) can be significantly facilitated by the hydrogen bond strengthening in the excited state.In the past years, most of the researches have been done on the hydrogen bond in the ground state. With the development of the experimental technology, the hydrogen bond in the excited state has become more and more interested by the scientists. To get better understand of the in the electronically excited state, diverse experimental and theoretical methods has been performed. Femtosecond time-resolved vibrational spectroscopy has shown potential to give a good insight into the microscopic dynamics and provided information on local structures. Time-dependent density functional theory (TDDFT) method has also been confirmed as a reliable method to investigate the hydrogen bond in the electronically excited state.In our work, the hydrogen bond and its effects in the excited state of three different molecular systems have been investigated by time-dependent density functional theory (TDDFT). For the 6-amino-3-((thiophen-2-yl) methylene)-Phthalide in methanol, we have theoretically demonstrated the intermolecular hydrogen bond C=O…H-0 of the 6-ATMPH-(MeOH)1 complex and the 6-ATMPH-(MeOH) 3 complex can be strengthened in the excited-state. The calculated hydrogen bond binding energies, the spectra shift of the stretching mode of the C=O and O-H group and the hydrogen bond lengths of different electronic states confirmed the mechanism of the hydrogen bond strengthening in the electronically excited state. We also theoretically demonstrated that the hydrogen bond N…H-O is weakened in the electronically excited-state of the 6-ATMPH-(MeOH)3 complex.We also investigated the hydrogen bond effects on the trans-4-hydroxy-4'-nitrostilbenes (trans-HN) and the1H-pyrrolo[3,2-h]quinoline (PQ) in the excited state. We found the cis-trans isomerization of the trans-HN is facilitated by the hydrogen bond strengthen in the excited state. In the excited state, the changes of the intermolecular hydrogen bond decide the inactivation path of the hydrogen-bonded complex. For the PQ-MeOH complex, we have investigated the mechanism of excited-state proton transfer (ESPT) through a hydrogen-bonded bridge using the TDDFT calculations. The ESDPT reaction is facilitated by the electronic excited-state hydrogen bond strengthening and the concerted mechanism of the ESDPT is reconfirmed in our work.