Single-Molecule Optical Memory using High-performance Photochromic Diarylethenes

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The ultimate goal of optical memory is to store optical information in each molecule. As the first step to the single-molecule optical memory, we carried out the synthesis of fluorescent photochromic molecules suitable for the optical memory and measured the photo-switching of fluorescence from the single molecules. The photochromic molecule should exhibit the following performance ; high photo-switching efficiency, a fatigue resistant property and a high fluorescent quantum yield. It is also required to reveal the detailed mechanism of single-molecule photochemistry. The results are as follows.(1) Fluorescent photochromic molecules having a fluorescent anthracene or perylene unit and a photochromic diarylethene unit were synthesized. When the two units are connected by an adamantyl group, the molecules exhibit efficient photo-switching performance and high fluorescent quantum yields. Molecules which show electron-transfer fluorescent quenching were also prepared.(2) The above newly synthesized molecules were dispersed in various polymer matrices and the photo-switching of fluorescence from the single molecules was measured. The fluorescence showed a digital photo-switching in two states and the response times(on and off times) were found to show a broad distribution. The distribution of the response times was studied theoretically in detail and attributed to local minima in both ground and excited energy diagrams. This finding surely provides a new insight into the photochemistry in polymer matrices.