Photoinduced electron transfer between C₆₀-pendant calixarene and captured electron donor: Improvement of electron-transfer efficiency by applying host-guest chemistry

A photoinduced electron transfer between C₆₀ connected with calixarene (calix-C₆₀) and a molecule in which aniline and ammonium are connected (ammonium aniline), in which the ammonium moiety is included in the calixarene, has been investigated. By connecting it with calixarene, C₆₀ is given the ability to interact with the primary alkylammonium. In the calix-C₆₀/ammonium aniline system, the calixarene moiety of calix-C₆₀ is capable of interacting with the ammonium moiety to form a donor-acceptor dyad via the cation-π-type inclusion mechanism in the solution. When a selective pulse laser irradiates the C₆₀ moiety of the calix-C₆₀/ammonium-aniline dyad, C₆₀ anion radical formation was observed in high quantum yield ( = 0.95). From transient spectroscopies, it is confirmed that the electron-transfer proceeds through the dissociation of the exciplex of ³(C₆₀-aniline)* in the calix-C₆₀/ammonium aniline system. By applying interaction between calixarene and ammonium, the electron transfer is accelerated in dyad, greatly increasing the quantum yield for electron transfer. The produced radical anion of the C₆₀ moiety persists for about 1 ms, and the back electron-transfer process obeys second-order kinetics, indicating that the radical anion of the C₆₀ moiety and the radical cation of the aniline moiety are solvated separately. A novel strategy for constructing a new class of efficient electron-transfer systems by using a calixarene as a reagent capture unit was demonstrated.