Photo- and electrochemical properties of newly synthesized thioxathone-viologen-fluorene ternary compound and its electrochromic device

External stimuli-responsive materials exhibit widespread potential applications in sensors, smart windows, displays, and opto-electronic molecular devices. In this study, we report light-/electrochemically induced chromic behaviors of newly synthesized ternary compound in the device. This compound is composed of a light-harvesting unit of thioxathone (TX), an electron donor of fluorene (FL), and an electron mediator of viologen (VIO), and thus it can act as a photochromic species with an intramolecular electron transfer under irradiation. The precursors of TX and FL substituents give off broad emissions at approximately 437 and 310−330 nm, respectively. Both emissions are largely quenched in the TX-VIO-FL ternary compound, which is caused by an intramolecular transduction of energy from the excited singlet FL and TX to the electroactive VIO substituent. Based on cyclic voltammogram of TX-VIO-FL modified electrodes, two reversible waves are observed at around −0.44 and −0.89 V (vs Hg/Hg2Cl2), attributed to the electron transport processes of TX-VIO2+-FL ↔ TX-VIO+•-FL and TX-VIO+•-FL ↔ TX-VIO0-FL, respectively. Sandwiched type of photo-/electrochromic devices are constructed, displaying a good transmittance and reversible viologen color change behavior under irradiation or an applied bias of -2.6 V.