Synthesis and photophysical properties of artificial photosynthesis and molecular switching devices.

摘要

Several multi-chromophore organic compounds were prepared as photosynthetic reaction center mimics and approaches to a molecular switch. Time-resolved absorption and emission spectroscopy were used to elucidate mechanisms of photo-induced electron and energy transfer in these compounds. A caroteno-porphyrin-fullerene molecular triad was prepared as a reaction center mimic. This compound was shown to undergo rapid photo-induced energy and/or electron transfer, depending on the solvent medium. The C•+-P-C60 •- state is formed with a yield of essentially unity, and demonstrates efficient conversion of light energy to electrochemical energy (potential). Electron transfer rates reveal a significant structural effect on thermodynamic driving force and electronic coupling, as compared to similar compounds in the literature. A porphyrin-indolino-benzospiropyran was also prepared as an approach to a molecular switch. Such spiropyrans are known to undergo a reversible photochromic reaction in solution. Fluorescence experiments indicate that this photochromic reaction provides a way to "switch" singlet-singlet energy transfer from the porphyrin moiety. That is, the porphyrin does not transfer excitation energy to the closed spiropyran, whereas the porphyrin transfers excitation energy to the spiropyran open form with a yield of 0.75. Finally, the preparation of a spiropyran-fullerene dyad is described. Photophysical investigations of this compound are currently underway. Knowledge gained from these investigations can be used to further the design of new photosynthesis mimics and molecular switching devices.