CH-p interaction-induced triplet excimer for enhanced phosphorescence bio-imaging

Triplet excimer-based organic room-temperature phosphorescence (RTP) materials with long-wavelength and long-lifetime emissions are highly valuable for in vivo imaging because of their good tissue penetration and signal-to-background ratio (SBR). However, triplet excimer-based RTP materials remain scarce, and the relationship between their structures and properties remains unclear. Here, we report a triplet excimer-based phosphor: B-PhBr. Our experimental results suggest that the triplet excimer in B-PhBr crystals is primarily accountable for its long-wavelength phosphorescence and that the CH-p interaction is crucial for the formation of the triplet excimer. Furthermore, benzophenone is selected as matrix to enhance the phosphorescence performance of the guest. The doping system demonstrates an ultralong organic phosphorescence that originates from the triplet excimer. With the aid of Pluronic F127, the doping system can be processed into aqueous nanoparticle dispersions and show great potential in bio-imaging, with a maximum SBR of 43.8 in subcutaneous bio-imaging in vivo.