Ultralong room temperature phosphorescence in Cd-MOFs regulated by the multimode coordination configuration of niacin ligand†

Long persistent luminescence (LPL) materials have attracted significant attention due to their potential applications in the fields of bioimaging, anti-counterfeiting and chemosensors. It is well known that the aggregation manner of ligands in MOFs directly affects their LPL properties. In this work, three MOFs named SUST-P1, SUST-P2 and SUST-P3 with LPL characteristics were constructed by niacin and Cd(II) salts via a simple solvothermal method. Importantly, the ligands in the three MOFs adopted different coordination models to connect metal ions/clusters, thereby generating distinct photophysical properties. The presence of binuclear cluster nodes in SUST-P1 was beneficial to intersystem crossing. SUST-P3 exhibited 2D-interpenetrating networks characterized by dense stacking, thereby inhibiting network motions. Consequently, the phosphorescence lifetimes of SUST-P1 and SUST-P3 were longer than SUST-P2, which involved ethanol and DMF molecules with high-energy vibrations. All MOFs exhibited phosphorescence emission around 500 nm with decay lifetimes of 190.37 ms (SUST-P1), 109.34 ms (SUST-P2) and 123.72 ms (SUST-P3) at 300 K, which increased to 357.58 ms, 173.12 ms and 241.14 ms at 77 K, respectively. Moreover, visible LPL performances were observed for the three MOFs under ambient conditions. Based on the LPL behavior, the obtained three MOFs could be applied in multiple information encryption and decryption.