Time-dependent density functional theory study on the coexistent intermolecular hydrogen-bonding and dihydrogen-bonding of the phenol-H2O-diethylmethylsilane complex in electronic excited states

Abstract

An intermolecular coexistent hydrogen bond and a dihydrogen bond of a novel phenol-H₂O-diethylmethylsilane (DEMS) complex in the electronically excited states were studied using the time-dependent density functional theory (TDDFT) method. Frontier molecular orbitals analysis revealed that the S₂ state of the dihydrogen-bonded phenol-H₂O-DEMS complex is a locally excited state in which only the phenol site is electronically excited. Upon electronic excitation, the O–H and H–Si vibrational modes are red shifted compared with those calculated for the ground state. The O–H and H–Si bonds involved in the dihydrogen bond O–H⋯H–Si and hydrogen bond O–H⋯O are longer in the S₂ state than in the ground state. The H⋯H and H⋯O distances significantly shorten in the S₂ state. Thus, both the intermolecular dihydrogen bond and the hydrogen bond of the phenol-H₂O-DEMS complex are stronger in the electronically excited state than in the ground state. In addition, the hydrogen bonding is favorable for the formation of the intermolecular dihydrogen bond in the ground state. However, they are competitive with each other in the electronically excited state.