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.