title: Photochromic phenoxyl-imidazolyl radical complexes with decoloration rates from tens of nanoseconds to seconds.
abstract: We report a novel photochromic molecular system, phenoxyl-imidazolyl radical complex (PIC), in which both a phenoxyl radical site and an imidazolyl radical site are reversibly and simultaneously generated upon UV light irradiation. PIC consists of the three parts: an aromatic linker, a diarylimidazole moiety, and a 4H-cyclohexadienone ring. Upon UV light irradiation, the C-N bond between the 4H-cyclohexadienone ring and the imidazole ring in the colorless closed-ring isomer of PIC undergoes a homolytic cleavage, leading to the formation of the transient colored open-ring isomer. Based on the substituents on the imidazoyl/4H-cyclohexadienone rings and the nature of the aromatic linker, the half-life of the colored open-ring isomer can be varied between tens of nanoseconds and seconds. PIC derivatives containing a 1,2-phenylene linker exhibit high fatigue resistance toward repeated photochromic reactions. Analysis using laser flash photolysis reveals that the absorption spectra of the open-ring isomers are not readily rationalized by a straightforward superposition of the spectra of the two component radical fragments and the photogenerated radicals are electronically coupled through the aromatic linker. Furthermore, the open-ring isomer can be treated as a hybrid of the pure open-shell biradical and closed-shell quinoid resonance structures.
authors: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
authors: Hiroaki
authors: H
authors: Yamashita
authors: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
authors: Takahiro
authors: T
authors: Ikezawa
authors: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
authors: Yoichi
authors: Y
authors: Kobayashi
authors: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.|‡CREST, Japan Science and Technology Agency (JST), K's Gobancho, 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan.
authors: Jiro
authors: J
authors: Abe