An interconversion system between imidazolium and imidazolinium has been proposed for the first time. Imidazolium and imidazolinium cations exhibit different reactivity due to the difference in the aromaticity and charge localization structure, which is successfully controlled by means of photoirradiation in the present system. A 4,5-dithiazolylimidazolium salt was prepared and studied as a new class of photochromic materials modulating electrostatic interactions and chemical reactivities. The photochromic 4,5-dithiazolylimidazolium showed reversible photoconversions between imidazolium open-form and imidazolinium closed-form upon successive irradiation with UV and visible light. The imidazolinium closed-form exhibited characteristic solvato- and ionochromisms in which the absorption maximum shifted by more than 80 nm depending on the solvent polarity and counteranions, whereas the imidazolium open-form showed no such solvent-dependent property. Because the corresponding nonionic 4,5-dithiazolylimidazole also did not exhibit the solvent-dependent absorption profile both in open- and closed-forms, the appearance of these chromisms in imidazolinium closed-form was attributed to the change in the extent of ionic interaction, which was brought about by the photoconversion of imidazolium to imidazolinium. The photoderived strong ionic interaction of imidazolinium with counteranion was further applied to the photocontrolled nucleophilic reaction system. Whereas the imidazolium open-form was inert to nucleophiles such as sodium methoxide, the imidazolinium closed-form was reactive to the nucleophilic reaction, demonstrating a photogated reaction system.
Photophysical Properties of a Terarylene Photoswitch with a Donor–Acceptor Conjugated Bridging Unit
作者:Rui Kanazawa、Takuya Nakashima、Tsuyoshi Kawai
DOI:10.1021/acs.jpca.7b00296
日期:2017.3.2
state potential energy surfaces, resulting in the excitation wavelength dependent photocyclization performance. The chemical modifications on the imidazole ring also had an effect on the fluorescence property in the open-ring forms, which is explained by the formation of different push–pull π-conjugation systems.