Tuning the excited-state intramolecular proton transfer (ESIPT)-based luminescence of metal-organic frameworks by metal nodes toward versatile photoluminescent applications

Here, using three metal cations (Mg2+, Al3+, and Zr4+) and an excited-state intramolecular proton transfer (ESIPT) active linker, 2,5-dihydroxyterephthalic acid (H2DHT), three luminescent metal-organic frameworks (LMOFs) were obtained. Importantly, their ESIPT-based luminescence originated from the linker was systematically tuned in emission profiles including intensity, emission color, and quantum efficiency in the solution as well as in the solid state, which is largely dependent on the composition and structural characteristics of these three LMOFs. Similar to the free linker, the Mg-based MOF possesses a relatively strong luminescence, the Al-based MOF has moderate luminescence due to the breathing effect, and the Zr-based MOF is very weakly luminescent, mainly caused by the LMCT process. Benefiting from unique emission behaviors of these three LMOFs, we further modulated their ESIPT-based luminescence through the interplay between guest species and components of LMOFs by combining with various photophysical processes, and successfully explored their potential applications as versatile photoluminescent platforms for target-triggered sensory materials, responsive fluorescent hydrogels, and white-light-emitting phosphors.