Facile design of poly(3,4-ethylenedioxythiophene)-tris(2,2′-bipyridine)ruthenium (II) composite film suitable for a three-dimensional light-harvesting system

It has been confirmed that octasulfonatocalix[8]arene (Calx-S8) and tris(2,2′-bipyridine)ruthenium (II) (Ru(bpy)32+) can form a stable host–guest complex in aqueous solution. The binding constant for 1:1 [Calx-S88−·Ru(bpy)32+]6− complex formation was estimated to be (2.4±0.8)×104 dm3 mol−1 by fluorescence titration, which indicates that the [Calx-S88−·Ru(bpy)32+]6− complex is the main species in 1:1 molar ratio aqueous solution of Calx-S8 and Ru(bpy)32+. In situ UV–Vis spectroscopic measurements indicated that Ru(bpy)32+ complexes can be readily deposited onto ITO electrode through electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) using [Calx-S88−·Ru(bpy)32+]6− host–guest complex as a dopant anion owing to the electrostatic interaction between the cationic conductive polymer and the anionic host–guest complex. The loading degree of the composite film with Ru(bpy)32+ can be determined by Lambert-Beer law modified for the two-dimensional concentration. The obtained composite film showed good photoelectric conversion properties in response to visible light irradiation. This is a novel photocurrent generation system in which the photoexcited state energy is efficiently collected by the conductive polymeric layer.