Photoelectrochemical Response of Polymer Langmuir−Blodgett Films Containing Tris(2,2‘-bipyridine)ruthenium(II) Complex

The tris(2,2‘-bipyridine)ruthenium(II) complex (Ru(bpy) 3 2+ ) derivative monomer was copolymerized with N - tert -pentylacrylamide and N -dodecylacrylamide. These copolymers, p( t PA-Ru) and p(DDA-Ru), formed stable condensed monolayers at the air/water interface. The monolayers could be successively transferred onto solid supports, yielding Y-type polymer LB films. The UV/vis absorption spectra of p(DDA-Ru) LB films indicated that Ru(bpy) 3 2+ chromophore can be safely incorporated into the polymer monolayer with a concentration of 3.9 × 10 -11 mol/cm 2, which is consistent with the results estimated from the surface pressure−area (π− A ) isotherms. The redox properties of the LB films were investigated by cyclic voltammetry. The cyclic voltammograms of the monolayers on the electrode show a well-defined symmetrical surface wave consisting of reversible redox peaks of Ru(bpy) 3 2+ at various potential scan rates. The surface concentrations of the redox active Ru(bpy) 3 2+ in the p( t PA-Ru) and p(DDA-Ru) monolayers were determined to be 3.3 × 10 -11 and 3.4 × 10 -11 mol/cm 2, respectively. On light irradiation of the LB films deposited on an ITO electrode in the presence of a sacrificial electron donor (thiosalythilic acid) in electrolyte solution, a large anodic photocurrent was observed with a rapid response to light intensity. The photocurrents as functions of light intensity, sacrificial donor concentration, and light wavelength (action spectrum) were measured. The photocurrent in the p( t PA-Ru) LB monolayer is produced more efficiently compared with that in p(DDA-Ru) system, which is explained by the molecular environment of Ru(bpy) 3 2+ complex in their monolayers. The conversion efficiencies of photons absorbed by Ru(bpy) 3 2+ to photocurrent in p(DDA-Ru) and p( t PA-Ru) monolayers were about 0.8% and 1.1%, respectively. The photoenergy conversion system based on the photoinduced electron transfer with Ru(bpy) 3 2+ was discussed.