Exciton Migration and Amplified Quenching on Two-Dimensional Metal–Organic Layers

The dimensionality dependency of
resonance energy transfer is of great interest due to its importance
in understanding energy transfer on cell membranes and in low-dimension
nanostructures. Light harvesting two-dimensional metal–organic
layers (2D-MOLs) and three-dimensional metal–organic frameworks
(3D-MOFs) provide comparative models to study such dimensionality
dependence with molecular accuracy. Here we report the construction
of 2D-MOLs and 3D-MOFs from a donor ligand 4,4′,4″-(benzene-1,3,5-triyl-tris­(ethyne-2,1-diyl))­tribenzoate
(BTE) and a doped acceptor ligand 3,3′,3″-nitro-4,4′,4″-(benzene-1,3,5-triyl-tris­(ethyne-2,1-diyl))­tribenzoate
(BTE-NO2). These 2D-MOLs and 3D-MOFs are connected by similar
hafnium clusters, with key differences in the topology and dimensionality
of the metal–ligand connection. Energy transfer from donors
to acceptors through the 2D-MOL or 3D-MOF skeletons is revealed by
measuring and modeling the fluorescence quenching of the donors. We
found that energy transfer in 3D-MOFs is more efficient than that
in 2D-MOLs, but excitons on 2D-MOLs are more accessible to external
quenchers as compared with those in 3D-MOFs. These results not only
provide support to theoretical analysis of energy transfer in low
dimensions, but also present opportunities to use efficient exciton
migration in 2D materials for light-harvesting and fluorescence sensing.