Photophysical and electrochemical properties of newly synthesized thioxathone-viologen binary derivatives and their photo-/electrochromic displays in ionic liquids and polymer gels

摘要

Thioxanthones (TXs) and viologens (VIOs) are important photo-sensitizers and electron mediators with interesting opto-electrochemical properties and potential applications for novel opto-electrical devices, displays, switches and sensors. Here, we reported the photophysical and electrochemical properties of newly synthesized TX-VIO binary derivatives, and their photo-/electrochromic displays in the ionic liquids and polymer gels. The precursor of TXBr (without the VIO substituent) gave off a blue light emission centered at about 437 nm with a quantum efficiency (QE) of approximately 0.2. For TX-VIOs, their QE was below 0.01; this significant luminescent quenching was attributed to an intramolecular energy transfer from the excited singlet state of TX to electroactive VIO. Thus, these TX-VIOs displayed good photochromic behaviors under ultraviolet and/or visible light radiation. Cyclic voltammograms of TX-VIOs showed two couples of chemically reversible waves centered at approximately -0.43 and -0.90 V (vs. Hg/Hg2Cl2). The former one was attributed to the electron transfer process of TX-VIO2+ <-> TX-VIO+& x2d9;, and the latter one to that of TX-VIO+& x2d9; <-> TX-VIO0 together with that of TX(red)-VIO2+ <-> TX(ox)-VIO2+. Finally, sandwiched types of transparent and flexible photo- and electrochromic devices were constructed with the use of TX-VIOs in the ionic liquids and polymeric gels as the light-sensitizer and color display layer. These devices displayed a good transmittance and good reversible color (pink, blue and colorless) change behavior under visible light radiation or an applied bias of -2.4 V.