Tunable Room Temperature Phosphorescence in Heavy-Atom-Free Metal–Organic Frameworks by Ligand Functionalization

Development of room-temperature phosphorescent metal-organic frameworks (MOFs) with free heavy metal atoms, high quantum yields, and long lifetime has been the focus of this research area. However, it is rare to develop methods to tune the intrinsic room temperature phosphorescence (RTP) of MOFs. Herein, it is demonstrated that heavy-atom-free CAU-10 MOFs with color-, lifetime-, and intensity-tunable intrinsic RTP can be achieved by ligand functionalization. By introducing an electron-donating substituent to isophthalic acid, the phosphorescence of CAU-10 MOFs can change from green to yellow with a lifetime ranging from 6.5 to 638 ms at ambient temperature. The strong metal-organic coordination bond and firm anchoring of ligands make the MOFs show superior RTP performance and stability compared to the crystals of pure organic ligands. Density functional theory calculations are applied to interpret the effect of ligand substituents on the luminescence of MOFs and reveal the emission difference among ligand molecules, ligand crystals, and MOFs. This work offers a new strategy to control the phosphorescence of MOFs, and emphasizes the advantages of structural tunability and stability of MOFs in the field of photoluminescence.