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

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 center dot center dot center dot H-Si lengthen slightly, while the C-O bond shortens. The calculated H center dot center dot center dot 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. (C) 2009 Elsevier B.V. All rights reserved.