Inspired
by natural photosynthesis, researchers have designed symmetric
metal–organic hosts with large inner pockets that are spontaneously
generated through preorganized ligands and functionalized metallocorners
to construct dye-containing host–guest systems. The abundant
noncovalent interaction sites in the pockets of the hosts facilitated
substrate–catalyst interactions for possible enrichment, fixation,
and activation of substrates/reagents, providing special electron
transfer pathways for regio- or stereoselectively photocatalytic chemical
transformations. In this Account, we focus our attention on metal–organic
hosts that contain photoactive or redox-active units to evaluate electron
transfer and charge separation between host and guest units in these
supramolecular systems and elucidate the related photoinduced chemical
reactions controlled by these electron transfer processes within the
structurally confined pockets of these interesting metal–organic
hosts.
We have been engaged in developing methods to isolate
a series
of chromophores for charge separation in supramolecular systems, incorporating
organic dyes as photosensitizers in metal–organic hosts with
electron acceptor/donor guests is a promising way to enable typical
enzyme-like photocatalytic transformations within a confined microenvironment.
Related to these inter- and intramolecular photoinduced electron transfer
(PET) processes, the formation of host–guest supramolecular
systems to fix and isolate the donor–acceptor pair with a short
through-space distance provided a new PET pathway to stabilize the
charge-separated ion pair. Highly efficient photosynthetic systems
can be obtained when charge transfer to electron donors/acceptors
occurs faster than the charge recombination. This Account starts with
a brief summary of the potential approaches for constructing photoactive
metal–organic hosts through the incorporation of dye molecules
within ligand backbones or as a part of the metal nodes of the architecture.
Following the methodological summary is a discussion on the mechanisms
governing the photoinduced charge separation and electron transfer
pathways within the dye-incorporated metal–organic hosts.
We also searched for strategies for constructing photoactive supramolecular
systems through encapsulating dye molecules within the inner space
of redox-active hosts. The photochemistry of these systems demonstrated
the following advantages due to the structural confinement: avoiding
excited state quenching caused by other chemical species, including
aggregated dyes, stabilizing the radical intermediate and tuning the
absorption or emission of the guest through electron/energy transfer
pathways. The photoinduced dye to redox-active host electron transfer
is a new and efficient pathway that is meaningful for chemists to
realize and understand many important enzymatic processes and to reveal
the secrets of a substance and energy metabolism in biological systems.
The confined interactions between the host and the guest have shown
fascinating effects of ...
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