We have developed procedures for the synthesis of push–pull azo-chromophores containing the s-triazolo[3,4-b]thiadiazole heterocycle compatible with the presence of electron-acceptor groups (nitrophenyl group) as substituents on both the triazole and thiadiazole rings. The linear and non-linear optical properties of the synthesized chromophores have been characterized by the EFISH technique, electro-optical absorption spectroscopy and DFT calculations. The combined results indicate a significant modulation of the properties of the chromophores depending on the substitution pattern on the heterobicycle. Fast UV-driven trans cis and slower thermally driven cis trans isomerizations around the N=N bond were observed and characterized for the chromophores.