We report light-facilitated reassembly to generate NIR-II luminescent materials without a light-reactive moiety for the first time. Three amphiphilic compounds 1–3 comprised of the NIR-I aza-BODIPY chromophore and β-glucosides were developed. The primary nanoparticles of aza-BODIPYs formed in water reassemble into J-aggregates under NIR laser irradiation. In comparison with amorphous nanoparticles, J-aggregates display red-shifted and enhanced emission, even extending emission into the NIR-II window (aza-BODIPY 2, 1030 nm). The mechanism study reveals that the reassemblies from primary nanoparticles to J-aggregates under 808 nm laser irradiation are caused by fast-elevated temperature due to the high photothermal conversion efficiency of aza-BODIPYs. Aza-BODIPY 2 is applied for NIR-II angiography with high-contrast in mouse vasculature. The light-facilitated reassembly of primary nanoparticles to form J-aggregates is achieved in vivo under laser irradiation. This new strategy to achieve NIR-II emission may inspire the exploration of novel NIR-II fluorescent materials for bioimaging.