Single-Molecule Optical Memory using High-performance Photochromic Diarylethenes

光存储的最终目标是在每个分子中存储光学信息。作为迈向单分子光存储的第一步，我们进行了适合于光存储的荧光光致变色分子的合成，并测量了单分子荧光的光开关。光致变色分子应表现出以下性能：高的光开关效率、抗疲劳性能和高的荧光量子产率。还需要揭示单分子光化学的详细机理。主要研究结果如下：(1)合成了含荧光基团的荧光光致变色分子和光致变色的二芳基乙烯分子。当两个单元通过金刚烷基连接时，分子表现出高效的光开关性能和高的荧光量子产率。将上述新合成的分子分散在不同的聚合物基质中，测量了单分子的荧光光开关。荧光显示出两种状态下的数字光开关，响应时间(开启和关闭时间)呈现出广泛的分布。从理论上详细研究了响应时间的分布，并将其归因于基能图和激发能图中的局部极小值。这一发现无疑为研究聚合物基质中的光化学提供了新的视角。

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.