Fluorescence imaging in near-infrared IIb (NIR-IIb, 1500–1700 nm) spectrum holds a great promise for tissue imaging. While few inorganic NIR-IIb fluorescent probes have been reported, their organic counterparts are still rarely developed, possibly due to the shortage of efficient materials with long emission wavelength. Herein, we propose a molecular design philosophy to explore pure organic NIR-IIb fluorophores by manipulation of the effects of twisted intramolecular charge transfer and aggregation-induced emission at the molecular and morphological levels. An organic fluorescent dye emitting up to 1600 nm with a quantum yield of 11.5% in the NIR-II region is developed. NIR-IIb fluorescence imaging of blood vessels and deeply-located intestinal tract of live mice based on organic dyes is achieved with high clarity and enhanced signal-to-background ratio. We hope this study will inspire further development on the evolution of pure organic NIR-IIb dyes for bio-imaging.

Unorthodox luminescent polymers without large π-conjugated structures, as promising soft luminescent materials, have recently received considerable attention owing to the availability of versatile preparation methods and their good processability. These polymers generally possess electron-rich moieties, with a diversity of intermolecular and intramolecular interactions through delocalized electrons. Therefore, polymerization itself can be an effective way to realize fluorescence emission. Here, polymerization-induced emission (PIE) is conceptualized as the process of transforming non-luminescent small molecules (i.e., monomers) into luminescent polymers. Correspondingly, PIE luminogens (PIEgens) with luminescent clusters, which are proposed as group aggregates with the minimum critical size for emission, require further investigation in order to understand the structure–emission relationships and related mechanisms. Promisingly, advanced polymerization methods offer unlimited opportunities to develop new soft luminescent polymers owing to the multi-level structures of polymers.