Electronic Excited-State Hydrogen Bonding Study Of The Ionic Liquids And Other Systems

Up to now, numerous experimental and theoretical methods have been launched to investigate the nature of hydrogen bond linking a solute with a polarizable functional group and a protic solvent. Intermolecular hydrogen bond, as a site-specific solute-solvent interaction, plays a fundamental role in molecular photochemistry of organic and biological chromophores in solution. Upon photoexcitation, the intermolecular hydrogen bond formed between solute and solvent molecules will reorganize themselves as the result of difference in charge distribution of the different electronic states, and this process is termed as hydrogen-bonding dynamics, which is concerned with the photochemistry and photophysics processes.In the present work, in order to investigate the electronic excited-state intermolecular hydrogen bonding between the chromophore coumarin153(C153) and the room-temperature ionic liquids N,N-Dimethylethanolammonium formate (DAF), both the geometric structures and infrared spectra of the hydrogen-bonded complex C153-DAF+in the excited states have been studied by the time-dependent density functional theory (TDDFT) method. We have theoretically demonstrated that the intermolecular hydrogen bond C1=O1…H1-O3in the hydrogen-bonded C153-DAF+complex is significantly strengthened in the Si state by monitoring spectra shifts of the C=O group and O-H group involved in the hydrogen bond C1=O1…H1-O3as well as the structure of the hydrogen-bonded C153-DAF+complex. The excited-state hydrogen bond strengthening of coumarin chromophore in ionic liquids is demonstrated theoretically for the first time.Time-dependent density function theory (TDDFT) was used to study the excitation energies in both singlet and triplet electronically excited states of Benzonitrile (BN),4-aminobenzonitrile (ABN), and4-dimethylaminobenzonitrile (DMABN) in methanol solvents. Only the intermolecular hydrogen bond C=N…H-O was involved in our system. A fairly accurate forecast of the hydrogen bond changes in low-lying electronically excited states were presented in light of a very thorough consideration of their related electronic spectra. The deduction we used to depict the trend of the hydrogen bond changes in excited states could help others understand hydrogen-bonding dynamics more effectively.In order to explore the effect of the hydrogen bond linking H2O and the structural unit together on the luminescence of the MOFs--[Ag2(pda)(dpe)2(H2O)]n·4nH2O, the geometric structure, electronic excitation, molecular orbitals, infrared spectrum, and NMR of the MOFs were studied. We have theoretically demonstrated that the hydrogen bond H…O are obviously strengthened in the excited state, and the coordination bond Ag—O are shortened significantly due to the strengthening of the hydrogen bond in S1state. Moreover, when the hydrogen-bonded complex is formed, the way of the deactivation transition in the excited state changes from the ligand-to-metal charge transfer (LMCT) coupled with intraligand charge transfer (LLCT) to LMCT. Meanwhile, the luminescence is demonstrated to be enhanced in this novel system under the behavior of the hydrogen bond in the excited state.