Efficient room-temperature phosphorescence of covalent organic frameworks through covalent halogen doping

Organic room-temperature phosphorescence, a spin-forbidden radiative process, has emerged as an interesting but rare phenomenon with multiple potential applications in optoelectronic devices, biosensing and anticounterfeiting. Covalent organic frameworks (C0F5) with accessible nanoscale porosity and precisely engineered topology can offer unique benefits in the design of phosphorescent materials, but these are presently unexplored. Here, we report an approach of covalent doping, whereby a COF is synthesized by copolymerization of halogenated and unsubstituted phenyldiboronic acids, allowing for random distribution of functionalized units at varying ratios, yielding highly phosphorescent COFs. Such controlled halogen doping enhances the intersystem crossing while minimizing triplet-triplet annihilation by diluting the phosphors. The rigidity of the COF suppresses vibrational relaxation and allows a high phosphorescence quantum yield (empty set(Phos) <= 29%) at room temperature. The permanent porosity of the COFs and the combination of the singlet and triplet emitting channels enable a highly efficient COF-based oxygen sensor, with an ultra-wide dynamic detection range (similar to 10(3)-10(-5) torr of partial oxygen pressure).

Automated summary

Organic room-temperature phosphorescence can be achieved by covalently synthesizing covalent organic frameworks (COFs) with halogen doping, which enhances phosphorescence and minimizes triplet-triplet annihilation. The rigidity of COFs suppresses vibrational relaxation, resulting in a high phosphorescence quantum yield at room temperature. COFs with permanent porosity and both singlet and triplet emitting channels can be used for highly efficient oxygen sensing.