Access to Highly Efficient Energy Transfer in Metal-Organic Frameworks via Mixed Linkers Approach.

Herein, we report a new light-harvesting mixed-ligand Zr(IV)-based metal-organic framework (MOF),with underlying fcu topology, encompassing the [Zr6(µ3-O)4(µ3-OH)4(O2C-)12] cluster and an equimolar mixture of thiadiazole- and benzimidazole-functionalized ligands. The successful integration of ligands with similar structural features but with notable chemical distinction afforded the attainment of a highly efficient energy transfer (ET). Notably, the very strong spectral overlap between the emission spectrum of benzimidazole (energy donor) and the absorption spectrum of thiadiazole (energy acceptor) provided an ideal platform to achieve very rapid (picosecond time scale) and highly efficient energy transfer (around 90% efficiency), as evidenced by time-resolved spectroscopy. Remarkably, the ultrafast time-resolved experiments quantified for the first time the anticipated close proximity of the two linkers with an average distance of 17 Å. This finding paves the way for the design and synthesis of periodic MOFs affording very efficient and fast ET to mimic natural photosynthetic systems.