Abstract

Through incorporation of electron transfer pairs in both the ground and excited states into redox active Werner type hosts with electronic acceptor/donor guests, the Duan group has developed a promising method to mimic natural enzyme systems in terms of redox transformations within a confined microenvironment. The host-guest systems fix and isolate the donor-acceptor pair with a short through-space separation, and without a through-bond electron transfer pathway. The confined electron transfer behavior differed from both the classical inter- or intramolecular photoinduced electron transfer (PET) processes that obey the Rehm-Weller or the Marcus theory. It has been proposed that this new electron transfer behavior assists in the stabilization of the charge-separated pair, which promotes redox transformations in both the ground and excited states. The unique communication between the dye guest and the host is direct confined PET from the excited state of the dye to the host, which could provide meaningful insight into the secrets of substance and energy metabolism in biological systems. Through modulation of the active site of nicotinamide adenine dinucleotide (NADH) models, the redox-active molecular host facilitated the confined electron transfer from the active sites of the NADH models to the substrate for biomimetic hydrogenation in the inner space of the host. The host-guest chemistry within the dye-containing metal-organic hosts permitted additional thermodynamic activation and modification of the electron transfer route for chemical reactions. The regiospecific and stereospecific PET processes within the host are at an early stage of development, however they have already proved important in the forging of organic reactions with tandem steps or intrinsic selectivity. By incorporating the oxidation catalyst and the aforementioned chiral group into one framework, an amphipathic framework-based host prompted the asymmetric dihydroxylation of aryl olefins.

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