Benzochalcodiazole-based donor-acceptor-donor non-symmetric small molecules as dual-functioning electrochromic and electrofluorochromic materials

Bifunctional fluorescent donor-pi-acceptor-donor molecules based on the benzoxadiazole (1) or benzothiadiazole (2) have been synthesized and characterized and the effect of chalcogen atom (oxygen vs. sulfur) was investigated. Both dyes exhibited dependence of both emission maxima and fluorescence quantum yield on the solvent polarity. The dyes were found to undergo an electropolymerization reaction when an electrochemical process was carried out in dichloromethane-based electrolyte and no electropolymerization was observed when propylene carbonate-based electrolyte was used. In the propylene-carbonate based electrolyte the fluorophores could be reversibly oxidized with the distinct color change from orange to green in case of 1 and yellow to green for compound 2 and the fluorescence was found to be quenched after electrooxidation. Both color change and quenching of luminescence were found to be reversible. The visible color, strong luminescence in the solid state and electroactivity of the dyes were ideal properties for dual electrochromic and electrofluorochromic applications. The constructed dual-functioning electrochromic and electrofluorochromic device could operate for upwards of 6 h in electrochromic mode, and upwards of 100 min in electrofluorochromic mode. The polymers obtained via electropolymerization were found to exhibit different properties in comparison to monomers.