†Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
‡Itoh Optical Industrial Co.,Ltd., 3-19 Miyanari-cho, Gamagori, Aichi 443-0041, Japan.
J Am Chem Soc. 2015 May 6;137(17):5674-7. doi: 10.1021/jacs.5b02862. Epub 2015 Apr 28.
Stepwise two-photon processes not only have great potential for efficient light harvesting but also can provide valuable insights into novel photochemical sciences. Here we have designed a [2.2]paracyclophane-bridged bis(imidazole dimer), a molecule that is composed of two photochromic units and absorbs two photons in a stepwise manner. The absorption of the first photon leads to the formation of a short-lived biradical species (half-life = 88 ms at 298 K), while the absorption of the additional photon by the biradical species triggers a subsequent photochromic reaction to afford a long-lived quinoid species. The short-lived biradical species and the long-lived quinoid species display significantly different absorption spectra and rates of the thermal back-reaction. The stepwise two-photon excitation process in this photochromic system can be initiated even by incoherent continuous-wave light irradiation, indicating that this two-photon reaction is highly efficient. Our molecule based on the bridged bis(imidazole dimer) unit should be a good candidate for multiphoton-gated optical materials.
逐步双光子过程不仅具有高效光捕获的巨大潜力，而且还可以为新颖的光化学科学提供有价值的见解。在这里，我们设计了一种[2.2]并环戊二烯桥联双（咪唑二聚体），该分子由两个光致变色单元组成，可逐步吸收两个光子。吸收第一个光子会导致短寿命双自由基物种的形成（在 298 K 下半衰期为 88 ms），而双自由基物种吸收额外的光子会引发后续的光致变色反应，从而生成长寿命醌型物种。短寿命双自由基物种和长寿命醌型物种显示出明显不同的吸收光谱和热逆反应速率。在该光致变色体系中，逐步双光子激发过程甚至可以由非相干连续波光辐照引发，表明这种双光子反应具有很高的效率。我们基于桥联双（咪唑二聚体）单元的分子应该是多光子门控光学材料的良好候选物。
