Ultrafast and single exponential responsive materials were achieved by encapsulating donor-acceptor linked molecules into cucurbitunitl, CB, as nanocavity hosts. Various aromatic groups were linked with various types of 4,4′-bipyridinium groups through propyloxy linker. They showed characteristic charge-transfer (CT) absorption with specific colors in aqueous solutions. Upon addition of CB, they showed remarkably different colors due to intramolecular CT complex formation in CB. Upon femtosecond laser excitation of CT band extremely fast electron transfer occurred from a donor to an acceptor unit accompanying new absorption in the visible to near-infrared region due mainly to photoreduced bipyridinium derivatives. Thermal back electron transfer reactions in CB were found to follow a single exponential decay with rate constants ranging more than two orders depending on the combination of a donor and an acceptor unit. Their rate constants vs. free energy changes for oxidized donors and reduced acceptors in linked molecules were expressed by the Marcus theory.
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