Photoelectrochemistry of a pigment used in artificial photosynthesis: An anilinocarotenoid

LB films of an amphipathic carotenoid, 7'-apo-7'-(4-aminophenyl)-beta -caro tene (H(2)APC), deposited on semiconducting transparent ITO electrodes, whe n immersed in electrolyte-containing benzoquinone (Q) and illuminated, prod uced photocurrents that were measured over the spectral range of 350-700 nm . The generated photocurrent was investigated as a function of different va riables: bias potential, number of LB layers, and concentration of Q in the surrounding electrolyte. Only cathodic photocurrents were observed with H2 APC. The action spectrum shows that the absorption of light by the caroteno id pigment is responsible for the photocurrent effects. The photoresponse i ncreases linearly with the number of LB layers deposited. The quantum yield of electron transfer is independent of the number of layers, indicating ef ficient charge and/or energy transfer between the layers. This result is un ique to carotenoids films. Anodic photocurrents were not detected even in t he presence of electron-donor couples. This behavior is in contrast to that observed with another amphipathic carotenoid, 7'-apo-7'(4-carboxyphenyl)-b eta -carotene (ACC), which generates photocurrents in either direction depe nding on the external couple.