Photochromism of Pentaarylbiimidazoles and Phenoxyl-Imidazolyl Radical Complexes
Considerable interest has been focused on organic photochromic materials that change their color upon irradiation with light; the photogenerated colored species can be reversed to the initial colorless species either by thermally or by subsequent irradiation with a specific wavelength of light. In particular, thermally reversible photochromic molecules offer the opportunity to change and reset the molecular properties by simply turning a light source on and off. Increasing the thermal-bleaching rate for thermally reversible photochromic molecules is essential for the development of revolutionary optical switching devices such as optical data processing and light modulators. We designed and synthesized a new type of fast photochromic molecules, pentaarylbiimidazole (PABI), and phenoxyl-imidazolyl radical complex (PIC). PABI and PIC show photoinduced homolytic bond cleavage of the C–N bond between the two imidazole rings or between the imidazole rings and the 4H-cyclohexadienone rings, respectively, and successive fast C–N bond formation. Moreover, they exhibit high fatigue resistance against repeated photochromic reactions. As compared with other photochromic molecules, these novel fast photochromic molecules are characterized by their diversity in molecular design and are promising materials for prospective fast light modulator applications.
KeywordsHexaarylbiimidazole Pentaarylbiimidazole Imidazole dimer Radical complex Fast photochromism Phenoxyl radical
This work was supported partly by the Core Research for Evolutionary Science and Technology (CREST) program of the Japan Science and Technology Agency (JST) and JSPS KAKENHI Grant Number JP26107010 in Scientific Research on Innovative Areas “Photosynergetics,” Japan. Financial assistance for this research was also provided by the MEXT-Supported Program for the Strategic Research Foundation at Private Universities, 2013–2017.
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