Fabricating of turquoise/white luminescent azo-Schiff bases bearing benzimidazole and imidazole rings

New azo dyes (1a-b) were prepared by the azo coupling reaction of 2-nitro-1,4-phenylenediamine with 5-chlorosalicylaldehyde and 5-chloro-2-hydroxyaniline. Corresponding Schiff base derivatives (2a-b) bearing conjugated benzimidazole and imidazole moieties were obtained via the condensation reaction of these dyes with 2-aminobenzimidazole and 4-imidazolecarboxaldehyde. Their structures were characterized by elemental analysis, FT–IR, 1H/13C NMR, LC-MS and UV–Vis spectroscopic techniques. Chromic (solvato-, acido-, thermo-) and photoluminescence behaviour of compounds 2a and 2b were evaluated depending on their donor–π–acceptor molecular system and intramolecular proton tautomerism. The absorption and emission spectra of 2a and 2b were recorded in DMSO, DMF and CHCl3. 2a emitted turquoise luminescence in DMSO and DMF, and white luminescence in CHCl3, while 2b emitted strong turquoise luminescence in only CHCl3.