Crystal Structures of Diethylamino Substituted Benzylideneanilines and Absorption Spectra of Their Related Derivatives

Abstract

X-ray crystal analysis of azomethine dyes, such as diethylamino substituted benzylideneanilines and their silicon chelates was investigated for the elucidation of the steric structure of benzylideneanilines having different substituents, and the relation between absorption spectra of those dyes and their steric structures.
Crystal structures of benzylideneaniline derivative, hydoroxybenzylideneaniline derivative, and their silicon chelate were determined by X-ray crystal analysis. The molecular structures of benzilydeneaniline derivative and hydroxybenzylideneaniline derivative was almost planar. Two neighbor molecules in the crystal of hydroxybenzylidenaniline faced each other and their oxygen-oxygen bond lengths was identical to that of hydroxybenzylidenaniline having ordinary hydrogen bonding.
For each dye, absorption spectrum in solution and diffuse reflection spectrum in solid were investigated. In a solution, the absorption spectrum of hydroxybenzilidenaniline derivative showed only a small red shift from benzilidenaniline derivative. In diffuse reflection spectra, on the other hand, hydroxybenzylideneaniline derivative had a new broad absorption peak, which was caused by hydrogen bonding in solid state. In the comparison of absorption spectra between silicon chelates and the corresponding ligands, the absorption maxima (λ_max) of the chelates had greater red shift and absorption width than the ligands in both solution and solid. The absorption spectrum of sublimed amorphous film was similar to that of the solution, but the sublimed crystalline film showed a red shifted spectrum.