Fluorescent Dyes with 2-Amino-4,7-diazaindole Skeleton: Synthesis and Spectroscopy

The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with compounds possessing two vicinal chlorine atoms activated toward nucleophilic substitution has been studied. All derivatives bearing a 2,3-dichloropyrazine moiety react with DBU leading to fluorescent dyes. Among others, only 2,3-dichloro-1,4-naphthoquinone reacts giving the expected pentacyclic product albeit in a very low yield and accompanied by the product of hydrolysis. Spectroscopic properties of the synthesized compounds were studied. The dye formed from 5,6-dichloro-2,3-dicyanopyrazine exhibits a very high Stokes shift and strong dependence of the fluorescence quantum yield on solvent polarity.