Syntheses and fluorescent properties of 2,5-diamino-3,6-dicyanopyrazine dyes

2,5-Diamino-3,6-dicyanopyrazine (2), a new fluorescent chromophore for functional dye materials, was synthesized by an oxidative coupling reaction of 2,3-diamino-3-(phenylthio)acrylonitrile (1). Compound 2 has a symmetrical structure and a strong intramolecular charge-transfer chromophoric system. It shows strong yellowish-green fluorescence in solution, and thus has good potential as a synthetic intermediate for fluorescent dye chromophores. Alkylation of the amino groups of 2 produced a bathochromic shift of λmax and resulted in red fluorescence in high quantum yield. On the contrary, acylation of the amino groups produced a hypsochromic shift of λmax, with blue fluorescence in high quantum yield. Modifications of the amino and cyano groups in 2 were studied in detail and many new fluorescent dyes were obtained. The absorption and fluorescent properties, together with fluorescence quantum yield of the substituted amino-3,6-dicyanopyrazines were correlated with their chemical structures.