Syntheses and spectral properties of non-planar bis(styryl)diazepine fluorescent dyes and related derivatives

New bis(styryl)dicyanodiazepine fluorescent dyes and related derivatives were synthesized by the condensation of 2,3-dicyano-5,7-dimethyl-6H-1,4-diazepine and related compounds with arylaldehydes. Their optimized molecular structures were evaluated by the MOPAC PM3 method and MO calculations were conducted by means of the ZINDO method. The bis(styryl) dye showed very broad visible absorption spectra with triple absorption maxima which can be considered to arise from splitting of the degenerate HOMO's. The effects of ring size and substituents on the absorption and fluorescence spectra of a series of new styryldiazepine dyes have been interpreted in terms of the non-planar diazepine component of the chromophoric system. The strong intramolecular charge transfer chromophoric system of these dyes exhibited an exceptionally large Stokes shift of more than 100 nm, which resulted in pure red fluorescence at wavelengths beyond 600 nm.