Light-selective multiple photochromic systems are important for advanced photoswitching of chemical reactions and biological activities. While UV light has been frequently utilized to induce photochromic reactions, visible light is energetically acceptable to avoid undesired reactions. However, many of the reported multiphotochromic systems still rely on UV light to induce at least a part of photochromic reactions. In this work, we designed a biphotochromic molecule showing intensity-dependent multiple coloration with a visible-light source by incorporating two T-type photochromic units; a colorless positive photochromophore and a colored negative photochromophore in a molecule. The negative photochromophore acts as a visible-light sensitizer for the positive photochromic reaction. The compound shows an intensity-dependent color change under visible-light irradiation. The weak visible-light excitation leads to gradual decoloration from orange to yellow, whereas intense laser excitation clearly changes the color to green. This characteristic photochromism can be achieved by control of the photochromic reaction rates of the negative and positive photochromic reactions. The combination of negative and positive photochromic reactions gives attractive important insight into the development of multiresponsive optical materials.

中文翻译：

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由负和正光致变色单元组成的双光致变色分子的强度相关光响应

光选择性多重光致变色系统对于化学反应和生物活动的高级光开关非常重要。虽然紫外光经常被用来诱导光致变色反应，但可见光在能量上是可接受的，以避免不希望的反应。然而，许多报道的多光致变色系统仍然依赖紫外线来诱导至少一部分光致变色反应。在这项工作中，我们设计了一种双光致变色分子，通过结合两个 T 型光致变色单元，在可见光源下显示出强度依赖的多重着色；分子中的无色正光致发色团和有色负光发色团。负光致变色团作为正光致变色反应的可见光敏化剂。该化合物在可见光照射下显示出强度依赖的颜色变化。弱可见光激发导致从橙色逐渐褪色到黄色，而强烈的激光激发明显将颜色变为绿色。这种特有的光致变色可以通过控制负和正光致变色反应的光致变色反应速率来实现。负和正光致变色反应的结合为多响应光学材料的开发提供了有吸引力的重要见解。这种特有的光致变色可以通过控制负和正光致变色反应的光致变色反应速率来实现。负和正光致变色反应的结合为多响应光学材料的开发提供了有吸引力的重要见解。这种特有的光致变色可以通过控制负和正光致变色反应的光致变色反应速率来实现。负和正光致变色反应的结合为多响应光学材料的开发提供了有吸引力的重要见解。