Time-dependent density functional theory study on the electronic excited-state hydrogen bonding dynamics of methyl acetate in aqueous solution

摘要

The time-dependent density functional theory (TDDFT) method has been carried out to investigate the hydrogen-bonding dynamics of methyl acetate (CH_3CO_2CH_3) in hydrogen-donating water solvent. The ground-state geometry optimizations, electronic transition energies and corresponding oscillation strengths of the low-lying electronically-excited states for the isolated CH_3CO_2CH_3 and H _2O monomers, the hydrogen-bonded CH_3CO_2CH _3-(H_2O)1, 2 complexes have been calculated using DFT and TDDFT methods respectively. One intermolecular hydrogen bond C=O?H-O is formed between CH_3CO_2CH_3 and one water molecule in CH_3CO_2CH_3-H_2O dimer. Meanwhile, in CH_3CO_2CH_3-(H _2O)_2 trimer, two intermolecular hydrogen bonds C=O?H-O are formed between CH_3CO_2CH_3 and two water molecules. By theoretically monitoring the excitation energy changes among the CH_3CO_2CH_3 monomer, the CH _3CO_2CH_3-H_2O dimer, and the CH _3CO_2CH_3-(H_2O)_2 trimer, we have demonstrated interestingly that in some electronically-excited states, the intermolecular hydrogen bonds are strengthened inducing electronic spectral redshifts, while in others weakened with electronic spectral blueshifts. The phenomenon that hydrogen bonds are strengthened in some electronic states while weakened in others can arouse further probe into CH_3CO _2CH_3-(H_2O)_(1, 2) complexes.