Thiazolothiazole Fluorophores Exhibiting Strong Fluorescence and Viologen-Like Reversible Electrochromism

The synthesis, electrochemical, and photophysical characterization of N,N′-dialkylated and N,N′-dibenzylated dipyridinium thiazolo[5,4-d]thiazole derivatives are reported. The thiazolothiazole viologens exhibit strong blue fluorescence with high quantum yields between 0.8–0.96. The dioctyl, dimethyl, and dibenzyl derivatives also show distinctive and reversible yellow to dark blue electrochromism at low reduction potentials. The fused bicyclic thiazolo[5,4-d]thiazole heterocycle allows the alkylated pyridinium groups to remain planar, strongly affecting their electrochemical properties. The singlet quantum yield is greatly enhanced with quaternarization of the peripheral 4-pyridyl groups (ΦF increases from 0.22 to 0.96) while long-lived fluorescence lifetimes were observed between 1.8–2.4 ns. The thiazolothiazole viologens have been characterized using cyclic voltammetry, UV–visible absorbance and fluorescence spectroscopy, spectroelectrochemistry, and time-resolved photoluminescence. The electrochromic p...