Non-linear photoresponses against excitation light intensity are important for the development of attractive photofunctional materials exhibiting high spatial selective photoswitching that is not affected by weak background light. Biphotochromic systems composed of two fast photochromic units have the potential to show a stepwise two-photon absorption process in which the optical properties can be non-linearly controlled by changing the excitation light conditions. Herein, we designed and synthesized novel bisnaphthopyran derivatives containing fast photoswitchable naphthopyran units. The bisnaphthopyran derivatives show a stepwise two-photon-induced photochromic reaction upon UV light irradiation accompanied by a drastic color change due to a large change in the molecular structure between the one-photon product and the two-photon product. Consequently, the color of the bisnaphthopyran derivatives can be non-linearly controlled by changing the excitation intensity. This characteristic photochromic property of the biphotochromic system provides important insight into advanced photoresponsive materials.

中文翻译：

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双萘并吡喃的逐步光致变色表现出与激发强度有关的颜色变化†

对于激发光强度的非线性光响应，对于开发具有不受空间背景光影响的高空间选择性光开关的有吸引力的光功能材料非常重要。由两个快速光致变色单元组成的双光致变色系统具有显示逐步的双光子吸收过程的潜力，其中可以通过更改激发光条件来非线性控制光学特性。在这里，我们设计和合成了新型的含有快速光开关的萘并吡喃单元的双萘并吡喃衍生物。由于在单光子产物和双光子产物之间分子结构的巨大变化，双萘并吡喃衍生物在紫外光照射下显示出逐步的双光子诱导的光致变色反应，伴随着剧烈的颜色变化。因此，可以通过改变激发强度来非线性地控制双萘并吡喃衍生物的颜色。双光致变色系统的这种特征性光致变色性质为高级光响应材料提供了重要的见识。