The photochromic behaviour of thienylpyrrole azo dyes in THF solutions was studied for the
first time. The photochromic properties are strongly dependent on the substitution pattern on
the dyes. Nitro-substituted thienylpyrrole azo dyes are particularly interesting since they
exhibit very fast colouration/decolouration processes. The activation energies of these
compounds are among the lowest values reported for heterocyclic azo dyes. These
compounds show aggregation phenomena in freshly prepared solutions of THF, which lead …