The synthesis and characterization of heterocyclic azo dyes derived from 5-N,N-dialkylamino-2,2′-bithiophene couplers

Heterocyclic azo dyes were synthesized by diazotation of several substituted anilines and coupling with 5-N,N-dialkylamino-2,2′-bithiophenes to give 4-phenylazo-5-N,N-dialkylamino-2,2′-bithiophenes. This reaction contrasts with the behavior of 5-alkoxy-2,2′-bithiophenes towards aryldiazonium salts which provides 5-phenylazo-5-alkoxy-2,2′-bithiophenes. The thermal stability of the derivatives was evaluated using thermogravimetric analysis and their solvatochromic behaviour was investigated in several solvents of different polarity. The experimental results indicate that the heterocyclic azo dyes could be used as thermally stable, solvatochromic probes.