DFT/TDDFT study on the excited-state hydrogen bonding dynamics of hydrogen-bonded complex formed by methyl cyanide and methanol

The time-dependent density functional theory (TDDFT) method was performed to investigate the hydrogen-bonding dynamics of methyl cyanide (MeCN) as hydrogen bond acceptor in hydrogen donating methanol (MeOH) solvent. The ground-state geometry optimizations, electronic transition energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated MeCN and MeOH monomers, the hydrogen-bonded MeCN–MeOH dimer and MeCN–2MeOH trimer are calculated by the DFT and TDDFT methods, respectively. According to Zhao’s rule on the excited-state hydrogen bonding dynamics, the intermolecular hydrogen bonds CN⋯HO are strengthened in electronically excited states of the hydrogen-bonded MeCN–MeOH dimer and MeCN–2MeOH trimer in that the excitation energy of the related excited states are lowered and electronic spectral redshifts are induced. Furthermore, the hydrogen bond strengthening in the electronically excited state plays an important role on the photochemistry of MeCN in solutions.