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-dodecylacrylam ide. These copolymers, p(tPA-Ru) and p(DDA-Ru), formed stable condensed mon olayers at the air/water interface, The monolayers could be successively tr ansferred onto solid supports, yielding Y-type polymer LB films. The UV/vis absorption spcctra of p(DDA-Ru) LB films indicated that Ru(bpy)(3)(2+) chr omophore can be safely incorporated into the polymer monolayer with a conce ntration of 3.9 x 10(-13) mol/cm(2), which is consistent with the results e stimated from the surface pressure-area (pi-A) isotherms. The redox propert ies of the LB films were investigated by cyclic voltammetry. The cyclic vol tammograms of the monolayers on the electrode show a well-defined symmetric al surface wave consisting of reversible redox peaks of Ru(bpy)(3)(2+) at v arious potential scan rates. The surface concentrations of the redox active Ru(bpy)(3)(2+) in the p(tPA-Ru) and p(DDA-Ru) monolayers were determined t o be 3.3 x 10(-11) and 3.3 x 10(-11) mol/cm(2), respectively. On light irra diation 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 int ensity. The photocurrents as functions of light intensity, sacrificial dono r concentration, and light wavelength (action spectrum) were measured. The photocurrent in the p(tPA-Ru) LB monolayer is produced more efficiently com pared with that in p(DDA-Ru) system, which is explained by the molecular en vironment of Ru(bpy)(3)(2+) complex in their monolayers. The conversion eff iciencies of photons absorbed by Ru(bpy)(3)(2+) to photocurrent in p(DDA-Ru ) and p(tPA-Ru) monolayers were about 0.8% and 1.1%, respectively. The phot oenergy conversion system based on the photoinduced electron transfer with Ru(bpy)(3)(2+) was discussed.