Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan.
Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
J Am Chem Soc. 2020 Jun 3;142(22):10132-10142. doi: 10.1021/jacs.0c02739. Epub 2020 May 15.
Photochromic materials have been widely used in various research fields because of their variety of photoswitching properties based on various molecular frameworks and bond breaking processes, such as homolysis and heterolysis. However, while a number of photochromic molecular frameworks have been reported so far, there are few reports on photochromic molecular frameworks that show both homolysis and heterolysis depending on the substituents with high durability. The biradicals and zwitterions generated by homolysis and heterolysis have different physical and chemical properties and different potential applications. Therefore, the rational photochromic molecular design to control the bond dissociation in the excited state on demand expands the versatility for photoswitch materials beyond the conventional photochromic molecular frameworks. In this study, we synthesized novel photochromic molecules based on the framework of a radical-dissociation-type photochromic molecule: phenoxyl-imidazolyl radical complex (PIC). While the conventional PIC shows the photoinduced homolysis, the substitution of a strong electron-donating moiety to the phenoxyl moiety enables the bond dissociation process to be switched from homolysis to heterolysis. This study gives a strategy for controlling the bond dissociation process of the excited state of photochromic systems, and the strategy enables us to develop further novel radical and zwitterionic photoswitches.
光致变色材料因其基于各种分子框架和键断裂过程（如均裂和异裂）的多种光开关性能而在各个研究领域得到了广泛应用。然而，尽管迄今为止已经报道了许多光致变色分子框架，但很少有报道涉及在高耐久性的取代基的影响下同时表现出均裂和异裂的光致变色分子框架。由均裂和异裂产生的自由基和两性离子具有不同的物理和化学性质以及不同的潜在应用。因此，合理的光致变色分子设计可以按需控制激发态中的键离解，从而使光开关材料的多功能性超越传统的光致变色分子框架。在本研究中，我们基于自由基离解型光致变色分子：苯氧自由基-咪唑基自由基配合物（PIC）的框架合成了新型光致变色分子。虽然传统的 PIC 表现出光诱导的均裂，但苯氧基团的取代强供电子基团可以使键离解过程从均裂切换到异裂。本研究为光致变色体系激发态的键离解过程的控制提供了一种策略，该策略使我们能够进一步开发新型自由基和两性离子光开关。
