Sophisticated electronic devices featuring molecule-based circuitry may one day be available, thanks in part to a Brazilian study. Chemists at the University of São Paulo have designed an electrochemical cell that functions as a logic gate (basic circuitry used in computation) that produces electrical output signals in response to light input signals. Basing their design on a dye-sensitized Grätzel-type cell normally used for photovoltaic conversion of sunlight into electricity, Luis F. O. Furtado, Koiti Araki, Henrique E. Toma, and coworkers constructed so-called XOR and INH logic gates that are triggered by light with 350-nm and 420-nm wavelengths (Angew. Chem. Int. Ed. 2006, 45, 3143). According to the team, the key to the design is a novel dye, a ruthenium pyrazine carboxylate material, that accepts rather than injects electrons into an adjacent semiconductor layer when the device is irradiated. That configuration enables the direction of the photocurrent output to be controlled by the wavelength of the light, they explain.