Red-Emissive Organic Room-Temperature Phosphorescence Material for Time-Resolved Luminescence Bioimaging

Organic room-temperature phosphorescence (RTP) materials have been used in high-resolution imaging. However, the development of long-wavelength-emis sion RTP materials in aqueous solution remains a challenge. Here, we report red-emissive RTP materials via integration of the ring-fusing effect and host–guest interaction. The fused-ring guest molecule showed a low triplet state for long-wavelength emission, and the host molecule can bridge the huge energy gap between the triplet and singlet state of guest molecules for highly efficient intersystem crossing processes. The fused-ring host–guest material showed red emission with a long lifetime up to 274 ms because of enhanced conjugation and restriction of intramolecular motion. The well-dispersed phosphorescent nanoparticles (NPs) with a uniform size of approximately 200 nm show good biocompatibility and low cytotoxicity. The NPs are applied to time-resolved luminescence imaging to eliminate background fluorescence interference in vitro and in vivo.