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.

The compelling demand for higher performance and lower cost in the optoelectronics industry has driven the development of organic semiconductors. Molecular crystalline semiconductors (MCSs), especially two-dimensional MCSs (2D-MCSs), possess intrinsic ordered structure, quantum confinement effect, high mobility, unique optical and electrical properties, and more ecological and cheaper production, which make great promises in high-performance optoelectronic applications. Here we provide a review of design principles and synthetic strategies for 2D-MCS materials, exploiting their potential as a revolution option in associated optoelectronic devices. The merits and limitations of each strategy are presented, and these molecular crystals are considered as a competitive choice for emerging semiconducting materials in information science. Finally, the current challenges and future perspectives in this field are also elaborated.