Modulating Room-Temperature Phosphorescence by Coordination Interactions and Structural Rigidity in Dual-Ligand MOFs

The development of room-temperature phosphorescent (RTP) functional materials based on metal-organic frameworks (MOFs) is of great significance for fundamental photophysical studies as well as applications in information encryption and anticounterfeiting. However, the regulatory mechanisms of coordination interactions and structural rigidity on the RTP behavior in MOFs remain poorly understood. In this study, a dual-ligand cooperative design strategy (M + L_C + L_X) was implemented, in which the direct coordination of the carboxylate ligand to the metal center and the rigidity of the framework were systematically modulated. Four novel Cd-MOFs were successfully constructed, achieving precise control over the RTP performance. SCXRD analysis combined with DFT calculations revealed that the direct coordination of L_C is essential for RTP activation, whereas the framework dimensionality and the suppression of terminal vibrational relaxation imparted by the auxiliary ligand predominantly govern the extension of triplet-state lifetimes up to 153 ms. In addition, by exploiting the distinct afterglow differences and time-dependent color evolution, a time-resolved information encryption and anticounterfeiting strategy was devised, greatly enhancing information security. This study for the first time elucidates the synergistic mechanism of coordination interactions and structural rigidity on RTP behavior in MOFs and provides insights for the rational design of high-performance RTP functional materials.