Hydrogen Bonding Effects on Vibrational Dynamics and Photochemistry in Selected Binary Molecular Complexes

Abstract

This brief review presents an overview and analysis of the
experimental studies performed recently in the laboratory of the authors
demonstrating the role of hydrogen bonding as a promotional factor for
intermolecular vibrational energy relaxation, and as a driving force for
the occurrences of specific reaction channels in binary molecular complexes.
Both vibrational and electronic spectroscopic methods have
been used, and measurements have been performed in the supersonic
jet expansion, in cold inert gas matrixes and also in suitable liquids
at room temperature. Pure and mixed dimers of two types of aromatic
chromophores, 7-azaindole and phenol, have been used as the model
molecular systems, which involve O–H···O, O–H···N and N–H···N types
of hydrogen bonds. The promotional effect of vibrational relaxation has
been demonstrated showing large broadening of either of the infrared
X–H stretching fundamentals of the donor groups in the hydrogenbonded
X–H···Y network of the binary complexes or broadening of the
fluorescence spectra upon excitations to single vibronic levels of the
isolated complexes in the gas phase and making comparisons with the
corresponding spectra of the monomers. A similar approach has been
adopted to demonstrate the promotion of photodissociation and charge
transfer reactions in binary complexes by hydrogen bonding.