Synthesis and UV–vis spectra of a new type of dye via a decarboxylative azo coupling reaction

Abstract

The azo coupling reactions between polymethoxycarbonyl(N-mesylaminovinyl)cyclopentadienyl potassium and aryldiazonium tetrafluoroborates with subsequent hydrolysis and decarboxylation of one ester group led to the formation of new polyene structures, specifically, isomeric 3- and 4-aminovinyl-5-hydrazonocyclopentadienes. The latter undergo cyclization on silica gel to give substituted 2-aryl-2H-cyclopenta[c]pyridazines. The resulting (2-arylhydrazono)cyclopenta-1,3-dienes are deep-red colored and may be of interest as dyes, particularly in dye-sensitized solar cells. The products were examined by UV–Vis spectroscopy and demonstrated large extinction co-efficients with absorption maxima in the range of 400–600nm. The single crystal X-ray data revealed a short NN bond length in the hydrazones, indicating strong conjugation between the donor and acceptor parts of the molecules.