Electrochemically-tuned luminescence of a [Ru(bpy) 2(tatp)] 2+-sensitized TiO 2 anode and its applications to photo-stimulated guanine/H 2O 2 fuel cells
A phenazine-containing Ru(II) complex [Ru(bpy) 2(tatp)] 2+ (bpy = 2,2′-bipyridine and tatp = 1,4,8,9-tetra-aza-triphenylene) is first applied to a modification of the nano-TiO 2/indium-tin oxide (ITO) electrode by the method of repetitive voltammetric sweeping. The resulting [Ru(bpy) 2(tatp)] 2+-modified TiO 2 electrode shows two pairs of well-defined redox waves and excellent electrocatalytic activity for the oxidation of guanine. [Ru(bpy) 2(tatp)] 2+ on TiO 2 surfaces exhibits intense absorbance and photoluminescence in visible region, revealed by absorption spectra, emission spectra and fluorescence microscope. While [Ru(bpy) 2(tatp)] 2+-sensitized TiO 2 is functionalized as an anode to combine with a continuous wave green laser via an optical microscope, the luminescence of Ru(II)-based excited states can be enhanced by the oxidation of guanine. Furthermore, the [Ru(bpy) 2(tatp)] 2+-sensitized TiO 2 electrode is used as photoanode and hemoglobin-modified single-walled carbon nanotubes (SWCNTs) as cathode for the elaboration of a photo-stimulated guanine/H 2O 2 fuel cell with a saturated KCl salt-bridge. It becomes evident that the photo-stimulated fuel cell performance depends strongly on the excited states of Ru(II) complex-sensitized anodes as well as the electrocatalytic oxidation of guanine. This study provides an electrochemically-tuned luminescence method for better evaluating contributions of the sensitizer excited states to photo-stimulated fuel cells.