The second near-infrared window in a 1 500–1 700 nm region (known as the NIR-IIb region) presents low autofluorescence and a deep penetration depth, enabling a potential technology for effective imaging and anticounterfeiting applications. However, existing NIR-IIb-emitted fluorescence materials remain limited and possess low luminescent properties. In implementing the enhanced ~1 525 nm emission of the Er (III) complex in a nonorganic solvent, an amphiphilic diblock copolymer (PEG₁₁₂–PAA₁₂) was initially synthesized to coordinate with Er (III), and then certain Yb (III) was doped to form the PEG–PAA–Er/Yb complex. The complex shows a dramatic fluorescent enhancement of ~250-fold at ~1 525 nm in D₂O than that in H₂O under 980-nm laser irradiation, which is ascribed to the following factors: (1) The substitution of H₂O by D₂O can suppress the quenching effect of H₂O at ~1 470 nm to achieve the emission of PEG–PAA–Er; (2) the doping of Yb (III) enables the co-luminescence effect to PEG–PAA–Er to improve NIR-IIb emission. Notably, the PEG–PAA–Er/Yb complex can construct molecular logic gates with logic functions and optical anticounterfeiting by using the abovementioned fluorescence changes.

Optical imaging possesses important implications for early disease diagnosis, timely disease treatment, and basic medical as well as biological research. Compared with the traditionary near-infrared (NIR-I) window (650–950 nm) optical imaging, the emerging second near-infrared (NIR-II) window optical imaging technology owns the great superiorities of non-invasiveness, non-ionizing radiation, and real-time dynamic imaging with the low biological interference, can significantly improve the tissue penetration depth and detection sensitivity, thus expecting to achieve accurate and precise diagnosis of major diseases. Inspired by the conspicuous superiorities, an increasing number of versatile NIR-II fluorophores have been legitimately designed and engineered for precisely deep-tissue mapping-mediated theranostics of life-threatening diseases. Organic semiconducting nanomaterials (OSNs) are derived from organic conjugated molecules with π-electron delocalized skeletons, which show greatly preponderant prospects in the biomedicine field due to the excellent photoelectric property, tunable energy bands, and fine biocompatibility. In this review, the superiorities of NIR-II fluorescence imaging using OSNs for brilliant visualization various of diseases, including tongue cancer, ovarian cancer, osteosarcoma, bacteria or pathogens infection, kidney dysfunction, rheumatoid arthritis, liver injury, and cerebrovascular function, are emphatically summarized. Finally, the reasonable prospects and persistent efforts for repurposing OSNs to facilitate the clinical translation of NIR-II fluorescence phototheranostics are outlined.

Photodynamic therapy (PDT) is a promising approach to treat cancer and microbial infections due to its minimal invasiveness, high spatiotemporal selectivity, tissue specificity, and low toxicity. Depending on the reactive oxygen species generation mechanisms, PDT can be classified as type I and type II. To date, most reported photosensitizers are based on the type II PDT mechanism, which produces toxic singlet oxygen and requires an abundant and continuous supply of oxygen molecules. Unfortunately, in typical solid tumor microenvironments, vascular abnormalities and rapid metabolisms lead to oxygen deficiency, severely compromising type II PDT's effectiveness. To address this issue, type I PDT with less oxygen consumption has been developed as an effective way to overcome the limitations of traditional type II PDT. In this contribution, we focus on the recent advances in type I organic semiconducting photosensitizers (OSPs), including organic semiconducting small molecules, conjugated polymers, and covalent organic frameworks for advanced hypoxia-tolerant PDT. The conceptual framework and general properties of these OSPs are firstly introduced, followed by introducing OSPs with different chemical structures for type I PDT. Finally, the overall conclusion, insightful perspective, and future direction of the efforts of OSPs for advanced biological applications are outlined.