Design, synthesis, and characterization of molecular electronic logic elements

Molecular logic elements, an optical switch, an OR gate and a NAND gate based on light-driven electron transfer process in reaction centers of photosynthetic bacteria, have been designed and synthesized chemically and characterized photophysically.; The tetrad molecule PZn-BIm-PH2-NIm is designed and synthesized to function as a two-photon molecular logic element---a NAND gate---that, in a sense, also mimics the photosynthetic process in the reaction center of higher plants: photosystem I and photosystem H. The two systems must operate simultaneously, so must the two porphyrin moieties in the tetrad molecule in order to achieve the ultimate charge separated state.; The triad C-P-NIm, which could function as a molecular OR gate on the nanosecond time scale, has also been designed and prepared. In benzonitrile solution, the final charge separated state is achieved via a two-step electron transfer process with a quantum yield of 0.33 and a lifetime of 430 ns.; Supramolecules based on porphyrin and fullerene (dyad P-C60 and triad P-C60-P) have been designed, synthesized, and photochemically characterized. The triad and dyad feature a simple and tight linkage through a single carbon between the porphyrin and C60 moieties so as to achieve efficient electron transfer and to maximize the yield of photochemical reactions. In principle, the triad P-C60-P can act as a light-intensity-dependent molecular switch as C60 can accumulate two electrons in the final charge separated state. The charge separation occurs by both direct electron transfer and energy transfer-electron transfer. The electron transfer step starting from 1C60 is approximately two times faster in the triad than in the dyad due to the extra porphyrin, which contributes an extra pathway to quench the 1C60 state.