Aggregation‐Induced Phosphorescent Imaging in the Second Near‐Infrared Window

The fluorescence imaging in the second near-infrared window (NIR-II, 1000–1700 nm) is a very promising and actively studied technique, whereas optical imaging via NIR-II phosphorescence has been seldom studied. Here, an aggregation-induced selective signal activation strategy is reported, which relies on switching of radiative mode of probe from weak fluorescence to strong NIR-II phosphorescence. Copper indium selenium (Cu-In-Se) quantum dots emit extremely weak fluorescence in isolated state, while their aggregation remarkably lights NIR-II phosphorescence up at ≈1045 nm with over 2.7 × 103-fold increase in luminescent lifetime. Aggregation-induced emission-mode-switching has been confirmed by encapsulating Cu-In-Se assembles with mesoporous silica nanoparticles (Cu-In-Se@MSN), displaying unique phosphorescence-type emission. NIR-II phosphorescence signals enable Cu-In-Se@MSN to exhibit impressive lifetime imaging and high-order branches of vessels can be accurately determined. Studies on the origin of radiative-mode-switching not only provide a new insight into photophysical process, but also may lay groundwork for designing smart NIR-II probes.