Chromophore Density Effects on Energy Transfer in Postsynthetically Modified Metal–Organic Frameworks

Metal–organic frameworks consisting of organized arrays of chromophores have emerged as promising light-harvesting materials. Interchromophore energy transfer efficiencies within these systems depend on numerous factors, such as spatial separation, dipole orientation, chromophore number, and donor-to-acceptor chromophore ratio. Here, we use steady-state and time-correlated single-photon counting spectroscopies to study energy transfer efficiencies in a series of postsynthetically modified UiO-67 MOFs as a function of two synthetically controllable factors: the chromophore density and donor-to-acceptor ratio. As the donor-to-acceptor ratio decreases, energy transfer efficiency increases, reaching values up to 100%. Additionally, decreasing the overall percentage of donor and acceptor chromophores maximizes the quantum yield of emission. The synthetic control provided by postsynthetic modification provides the ability to elucidate general photophysical principles guiding energy transfer within donor–acceptor light-harvesting MOFs.