Unusual Negative Photochromism via a Short-Lived Imidazolyl Radical of 1,1′-Binaphthyl-Bridged Imidazole Dimer

• Published in: Journal of the American Chemical Society 2013-02, Vol.135 (8), p.3164-3172
• Main Authors: Hatano, Sayaka, Horino, Takeru, Tokita, Atsuhiro, Oshima, Toyoji, Abe, Jiro
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja311344u

We have synthesized a new photochromic compound that exhibits unusual negative photo­chromism, in which the stable colored species photo­chemically converts into the metastable colorless species via a short-lived radical. This compound has a 1,1′-bi­naphthyl moiety bridging the two diphenyl­imid­azole units. Its photo­chemical properties were investigated by nanosecond laser flash photolysis. The colored species isomerizes to the colorless species upon exposure to visible light and thermally returns to the original colored species within 20 min at room temperature. Moreover, the photodecoloration reaction proceeds via a short-lived radical with a half-life of 9.4 μs in benzene at room temperature. Both the colored and colorless species show the photo­induced homolytic bond cleavage reaction of the C–N bond between the nitrogen atom of the imid­azole ring and the carbon atom of the 1-position of the 1,1′-bi­naphthyl moiety and that of the C–C bond between each of the carbon atoms of the 2-position of the imid­azole ring, respectively, followed by their formation by rapid radical coupling.