Ultralong Near Infrared Room Temperature Phosphorescence in Cu(I) Metal-Organic Framework Based-on D-π-A-π-D Linkers

Materials taking abundant advantage of triplet states luminescence have risen lots of attention in decades. In this work, a Cu(I) metal-organic framework (MOF) with synchronous metal-to-ligand charge transfer (MLCT) state and triplet emission of the ligand is synthesized from a D-pi-A-pi-D ligand with suitable energy gap. The Cu(I) MOF possessed MLCT emission in the range of 450-505 nm with microsecond lifetimes (1.07 to 5.38 mu s) and a triplet state emission in near infrared (NIR) region approximate to 705 nm with lifetimes of 1.85 ms at 300 K and 25.16 ms at 77 K, much longer than those of reported Cu(I) MOFs. Moreover, a white light is obtained through adjusting the relative intensity of dual peaks. More importantly, NIR long persistent luminescence of Cu-MOF is observed by naked eyes under cryogenic condition. Multiple factors such as the delicate design of the D-pi-A-pi-D structure of ligand, the enhanced spin-orbital coupling by Cu(I) networks, and the tight packing mode of the framework promote the generation of MLCT emission and ultralong NIR room temperature phosphorescence. The combination of calculation and experiment to analyse the luminescence mechanism of Cu(I) MOFs provides ideas for the development of Cu(I)-based intelligently responsive materials with RTP properties.