Graphical Abstract Synthesis and characterization of novel diazenes bearing pyrrole, thiophene and thiazole heterocycles as efficient photochromic and nonlinear optical (NLO) materials M. Manuela M. Raposo, A. Maurício C. Fonseca, M. Cidália R. Castro, M. Belsley, M. Fátima S. Cardoso, Luís M. Carvalho and Paulo J. Coelho N R 1 N R 2 N R 3 R 1 = H, thienyl R 2 = alkyl, aryl R 3 = aryl, thiazolyl