We have developed a photoelectric conversion device which functioned as molecular logic gates. It consisted of a mixed self-assembled monolayer (SAM) of tris(2,2'-bipyridine)ruthenium(II)-viologen linked thiol and phthalocyanine thiol compounds. Photocurrents from the SAM could be controlled by an excitation wavelength as well as an applied potential. As molecular logic devices, two kinds of light emitting diodes (LEDs) were used as light sources. Photocurrents at E=0 V clearly responded as the XOR logic gate whereas those at -0.2 V as the OR logic gate. (c) 2005 Elsevier B.V. All rights reserved.