Interpretation of Absorption Spectra of Some Bisazomethine Dyes in a Crystalline State in Terms of Conformational Change and Exciton Interaction

Absorption properties of 13 bisazomethine dyes in a crystalline state were studied by optical waveguide spectroscopy. Their solid-state absorption spectra were found to shift bathochromically relative to those in solution with no remarkable change in a spectral shape. The observed spectral shifts were characterized in terms of two intermolecular interactions, conformational change and exciton interaction, on the basis of the crystal structure. Solid-state fluorescence properties of the diethylamino derivatives were also examined for their electronic characterization. The characteristic two-dimensional staircase structure, one of the proposed structures of Jaggregates, was found to play a significant role in the bathochromic spectral shift of all the bisazomethine derivatives.