Internal Compression Effects. II. Frequency and Intensity Changes in Charge-Transfer and Hydrogen-Bonded Complex Spectra

Some effects on spectra of weak molecular complexes due to compression of the complex bond were investigated. Changes in the charge-transfer (CT) frequency and intensity with changing bond length in model tetracyanoethylene-aromatic complexes have been estimated. These changes are related to a reduction of the complex bond length by internal compression forces of solvent (or by high external pressure). Variation of CT band frequency with compressional forces in various nonpolar solvents was studied, as was the stretching frequency of H bonds. It is concluded that solvent forces can contribute importantly to vapor-to-liquid spectral changes in weak complexes.