Pure Organic Room Temperature Phosphorescence from Excited Dimers in Self-Assembled Nanoparticles under Visible and Near-Infrared Irradiation in Water

Pure
organic room temperature phosphorescence (RTP) has unique
advantages and various potential applications. However, it is challengeable
to achieve organic RTP under visible and near-infrared (NIR)-light
excitation, especially in aqueous solution. Herein we assemble difluoroboron
β-diketonate compounds to form organic nanoparticles (NPs) in
water. The resulting NPs are able to show efficient RTP, effective
uptake, and bright imaging of HeLa cells under both visible- and NIR-light
excitation. More strikingly, spectroscopic study, single-crystal X-ray
diffraction, and DFT calculation reveal that the efficient RTP in
organic NPs is originated from dimers in their excited states. The
multiple interactions and intermolecular charge transfer in the dimer
structures are of significance in promoting the production of dimer
triplet excited states and suppressing the nonradiative decays to
boost the RTP under visible- and NIR-light irradiation in water.