Dye sensitized membranes within mesoporous TiO2: Photocurrents in aqueous solution

Mesoporous TiO2 film electrodes were modified with membranes consisting of alkyl phosphonic acids with either a sulphonate or pyridinium head group. Dyes (substituted porphyrins (1, 2, and 3), a substituted chlorin (4) and a substituted Ru tris-bipyridyl complex (5)) with tailored ionic (carboxylates, sulfonates, and ammonium) and hydrophobic functionalities were synthesized. The membrane modified electrodes were loaded with these dyes by self-assembling based on mutual charge compensation and hydrophobic interactions. The membrane electrodes can generate photocurrents upon white light illumination (16.5 mW/cm2) in the range of 20–50 μA/cm2 in aqueous 0.1 M KI solution. Dyes 3 and 4 perform better on the pyridinium membrane than directly attached via their carboxylate functionality. This demonstrates charge injection through the membrane into the conduction band of TiO2. ZINDO/S calculations indicate that the pyridinium head group assists this process.