Dicyanopyrazine studies. Part IV: Syntheses and solid state absorption spectra of new dicyanopyrazine dyes derived from dichlorodicyanopyrazine and Fisher's type bases

2-Chloro-5,6-dicyano-3-[2'-(1',3',3'-trimethylindolinylidine) methyl]pyrazine 3a showed large differences in lambda(max) from solution to solid state resulting from strong intermolecular pi-pi interactions. Related derivatives were synthesized by the nucleophilic substitution of 2,3-dichloro-5,6-dicyanopyrazine 1 with various Fisher's base type enamines. Absorption spectra, fluorescent properties and other physical properties were correlated with their chemical structures. The Pariser-Parr-Pople molecular orbital and MOPAC approach to evaluate their absorption spectra correlate with their conformations were conducted. Good correlation between the calculated and the experimental results were obtained. The substituent effects of dicyanopyrazines affecting their chemical, electronic, and physical properties were also studied. (C) 1998 Elsevier Science Ltd.