イミダゾリルラジカルを基盤とする高機能フォトクロミック分子の高次複合光応答

抄録

In recent years, the cooperative interaction between photons and molecules, “photosynergetic” effect, has received increased attention. Chemists have extensively explored photofunctional materials from fundamental and applicative perspectives to establish attractive molecular systems for efficient light energy conversion. However, the conventional photochemical reaction cannot fully utilize the photon energy absorbed by matter because a higher exited state thermally deactivates to a lowest excited state, which is well-known as Kasha’s rule. Therefore, one of the important challenges in recent photochemistry is to establish a basic principle and systems based on advanced photoresponse beyond a one-photon reaction of a single chromophore. Photochromic molecules are one of the molecular classes which show reversible color changes arising from the molecular structural isomerization upon light irradiation. We have developed fast switchable photochromic molecular systems based on imidazolyl radicals, bridged imidazole dimer, pentaarylbiimidazole, and phenoxyl-imidazolyl radical complex. The tunable thermal back reaction rate from microsecond to second time scales enables the applications as a light trigger to various research fields. In addition, we have recently developed the stepwise two-photon induced fast photochromism by using the electron transfer from a higher excited state of sensitizer or the effective electronic interaction between the photogenerated transient radicals. The development of stepwise photochromic compounds based on the above concepts will offer various attractive photofunctional materials. This article overviews the studies about fast photochromic molecules based on imidazole radicals and recent development of the high-performance fast photochromic molecules by photosynergetic effect.