Time-dependent density functional theory study of the excited-state dihydrogen bond O–H⋯H–Si

Abstract

Intermolecular dihydrogen bonding in the electronically excited states of a phenol–diethylmethylsilane (DEMS) complex was studied theoretically using the time-dependent density functional theory (TDDFT) method. Analysis of the frontier molecular orbitals revealed a locally excited S 1 state for the dihydrogen-bonded phenol–DEMS complex in which only the phenol moiety is electronically excited. The calculated infrared spectrum of the phenol–DEMS complex is quite different from that of previously studied S 1 state of a dihydrogen-bonded phenol–borane-trimethylamine complex. The O–H and Si–H stretching vibrational modes appear as intense, sharp peaks for the S 1 state which are slightly red-shifted compared with those predicted for the ground state. Upon electronic excitation to the S 1 state, the O–H and Si–H bonds involved in the dihydrogen bond O–H⋯H–Si lengthen slightly, while the C–O bond shortens. The calculated H⋯H distance is significantly shorter in the S 1 state than in the ground state. Thus, the intermolecular dihydrogen bond of the phenol–DEMS complex is stronger in the electronically excited state than in the ground state.