Photomodulation of the proton affinity and acid gated photochromism of a novel dimethylaminophenyl thiazole diarylethene

The acid-gated photochromism and the photomodulation of fluorescence and proton affinity of a novel dimethylaminophenyl thiazole diarylethene in MeCN were investigated from a kinetic point of view. Photomodulation of the proton affinities has been estimated from acid titrations and numerical modelling of the acid induced T-photochromism. The basicities of the thiazole and dimethylamino protonation sites are different by only one pK unit. Upon ring- closure, their relative proton affinities are reversed. Our investigations underline the role of the thiazole protonation in the carbon-carbon bond weakening of the closed form and validate the role of the proton as catalyst in the gated T-photochromism.

► A novel 2-aryl-4,5-bis(benzo[b]thiophen-3-yl)thiazole has been efficiently synthesised. ► The novel trisubstituted thiazole exhibits acid-gated P-type photochromism. ► Cycling between the ring-opened and ring-closed forms of the substituted thiazole results in modulation of fluorescence. ► The basicity of the pendant dimethylamino group and the thiazole ring N-atom are markedly influenced by photochromic cycling. ► Protonation of the thiazole ring N-atom promotes T-type photochromism of the system.