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+˙, and the latter one to that of TX–VIO+˙ ↔ 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.
Selective oxidation of organic sulfide under mild conditions has attracted growing attention because of its potential applications for the chemical transformation and degradation of toxic organics. Thioxanthones (TXs) are important photosensitizers for the photocatalytic oxidation of organic sulfides. This paper reports the fabrication of TX-functionalized silica nanocomposites, using a bottom-up self-assembling technique, and their application as heterogeneous photocatalysts for the selective oxidation of sulfides into sulfoxides. Two types of TXs, 3-hydroxy- 9H -thioxanthen-9-one (TXOH) and 9-oxo- 9H -thioxanthene-2,7-dicarboxylic acid (TXCOOH), were synthesized, and their monolayers were anchored covalently on the surface of silica nanoparticles (nanoSiO 2 ) via surface silanization and substitution reactions. The produced nanoSiO 2 TX and nanoSiO 2 TXCOOH composites emitted blue luminescence with an emission wavelength at approximately 430−434 nm; they exhibited a ∼10 nm red shift compared to TXOH and TXCOOH. Both nanocomposites acted as heterogeneous photocatalysts for the selective oxidation of aromatic thioethers into sulfoxides under mild conditions (radiation, air atmosphere, and room temperature). Good conversion efficiency and selectivity were obtained, particularly for those aromatic thioethers with benzyl- and electron-donating substituents. Since the TX monolayer was anchored covalently on the surface of nanoSiO 2 particles, the nanocomposites displayed good reusability and recyclability, in addition to facile separation of the reagents and photocatalysts from the reaction system.
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