Ortho-Nitrobenzaldehyde 1:1 Water Complexes. The Influence of Solute Water Interactions in the Vertical Excited Spectrum

The intermolecular hydrogen bonding interaction of a water molecule with the caging group ortho-nitrobenzaldehyde (o-NBA) has been studied by means of quantum mechanical Methods. The o-NBA chromophore presents two functional groups, NO2 and CHO, interconnected by ail intramolecular hydrogen bond. Both groups compete for the interaction with the solvent molecule, leading to eleven possible stable isomers that are very close in energy. The effect of the binding water on the electronic properties of o-NBA has been analyzed in structural terms as well as Using the atoms-in-molecules theory of Bader. Binding energies for all complexes are reported, and in general they range from 5 to 13 kJ/mol. Special attention has been paid to the effect of the water molecule on the vertical excitation energies of o-NBA. Upon water complexation the absorption spectrum of o-NBA shifts to higher energies and it is characterized by three bands of comparable intensities as those recently Measured for o-NBA in gas phase.