Triplet transfer across a surface-anchored metal-organic-framework heterojunction is demonstrated by the observation of triplet-triplet annihilation photon -upconversion in a sensitizer-emitter heterostructure. Upconversion thresholds under 1 mW cm are achieved. In the broader context, the double-electron-exchange mechanism of triplet transfer indicates that the heterojunction quality is sufficient for electrons to move between layers in this solution-processed crystalline heterostructure.

Efficient photon harvesting materials require easy-to-deposit materials exhibiting good absorption and excited-state transport properties. We demonstrate an organic thin-film material system, a palladium-porphyrin based surface-anchored metal-organic framework (SURMOF) thin film, that meets these requirements. Systematic investigations using transient absorption spectroscopy confirm that triplets are very mobile within single crystalline domains; a detailed analysis reveals a triplet transfer rate on the order of 10 10 s-1. The crystalline nature of the SURMOFs also allows a thorough theoretical analysis using density functional theory (DFT). The theoretical results reveal that the intermolecular exciton transfer can be described by a Dexter electron exchange mechanism that is considerably enhanced by virtual charge-transfer exciton intermediates. Based on the photophysical results, we predict exciton diffusion lengths on the order of several micrometers in perfectly ordered, single-crystalline SURMOFs. In the presently available samples, strong interactions of excitons with domain boundaries present in these metal-organic thin films limit the diffusion length to the diameter of these two-dimensional grains, which amount to about 100 nm. These results demonstrate potential of SURMOFs for energy harvesting applications.

Upon prolonged illumination photoproducts are created in porphyrin-based metal–organic frameworks that limit the triplet exciton lifetime by charge-transfer quenching.

Organic chromophores that exhibit aggregation-induced emission (AIE) are of interest for applications in displays, lighting, and sensing, because they can maintain efficient emission at high molecular concentrations in the solid state. Such advantages over conventional chromophores could allow thinner conversion layers of AIE chromophores to be realized, with benefits in terms of the efficiency of the optical outcoupling, thermal management, and response times. However, it is difficult to create large-area optical quality thin films of efficiently performing AIE chromophores. Here, we demonstrate that this can be achieved by using a surface-anchored metal-organic framework (SURMOF) thin film coating as a host substrate, into which the tetraphenylethylene (TPE)-based AIE chromophore can be printed. We demonstrate that the SURMOF constrains the AIE-chromophore molecular conformation, affording efficient performance even at low loading densities in the SURMOF. As the loading density of the AIE chromophore in the SURMOF is increased, its absorption and emission spectra are tuned due to increased interaction between AIE molecules, but the high photoluminescent quantum yield (PLQY = 50% for this AIE chromophore) is maintained. Lastly, we demonstrate that patterns of the AIE chromophore with 70 μm feature sizes can be easily created by inkjet printing onto the SURMOF substrate. These results foreshadow novel possibilities for the creation of patterned phosphor thin films utilizing AIE chromophores for display or lighting applications.