Synthesis and properties of new styryl dyes derived from 2,3-dicyano-5-methylpyrazines

Reaction of 2,3-dicyano-5-methylpyrazine derivatives (3a-e) with arylaldehydes gave new florescent styryl dyes (4-8). These styryl dyes have extended pi-conjugated systems and are strong intramolecular charge-transfer chromophoric systems. They are of interest as non-linear optical materials, which should produce a large dipole moment in the excited state, and consequently induce large dipole moment differences accompanying laser irradiation. The styryl dyes derived from 2,3-dicyano-6-hydroxy-5-methylpyrazine showed large solvatochromism, depending on the polarity of the solvent, due to tautomerism between the hydroxypyrazine and the pyridone forms. The fluorescence and solvatochromism properties of dyes 4-8 were also studied, and structure-property relationships in solution an din the solid state were evaluated on the basis of molecular stacking in the solid state. (C) 1996 Elsevier Science Ltd