Rigid Graphene Nanoribbons Enable Efficient Near-Infrared Room-Temperature Phosphorescence Emission

Triggering near-infrared (NIR) room-temperature phosphorescence (RTP) poses a major challenge, because the narrow optical gap promotes nonradiative decay via thermal vibrations. Here, we report a series of high-performance RTP materials based on graphene nanoribbons, namely <i>n</i>HBT (<i>n</i> = 1-4). Unlike the modulation of fluorescence by extending π-conjugation, enhancing molecular conjugation more effectively induces red-shifted phosphorescence, enabling NIR emission. By doping <i>n</i>HBT in polyvinylpyrrolidone, NIR RTP with a maximum emission wavelength of 898 nm is achieved, exhibiting a quantum yield of 2.9% and a lifetime of 1.9 ms. Moreover, the rigid fused-ring framework suppresses molecular motions and nonradiative decay, resulting in a persistent afterglow even at 377 K. Well-dispersed NIR RTP nanoparticles were further obtained using polystyrene-<i>b</i>-poly(ethylene glycol) as the host and surfactant. <i>In vivo</i> studies demonstrate excellent capability to suppress background fluorescence, achieving a signal-to-background ratio as high as 47.3 ± 4.2. These results highlight rigid graphene nanoribbons as a versatile platform for high-performance NIR RTP and biophotonic applications.