Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 137, Issue 15, Pages 4952-4955Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.5b02353
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Funding
- Core Research for Evolutionary Science and Technology (CREST) program of the Japan Science and Technology Agency (JST)
- MEXT, Japan [26107010]
- MEXT
- Grants-in-Aid for Scientific Research [26107010, 26620073, 15K17846] Funding Source: KAKEN
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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 CN 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.
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