Tautomerism and fluorescent properties of aminovinylpyrazine dyes

We have reacted diaminomaleonitrile with pyruvic aldehyde or pyruvic acid to produce 2, 3‐dicyano‐5‐methylpyrazine and 2, 3‐dicyano‐6‐hydroxy‐5‐methylpyrazine. Although these compounds showed no fluorescence, condensation with arylaldehyde yielded red to violet coloured styryl‐type dyes with strong orange to red fluorescence. We have investigated the tautomerism and fluorescent properties of these new pyrazine dyes by means of computer simulation, and have also investigated their spectral properties using molecular orbital and molecular mechanics calculation techniques. These studies revealed the dyes to have strong intramolecular charge‐transfer chromophoric systems and high solvatochromism both in absorption and fluorescence spectra.