Recent advances in benzo[a]phenoxazine-based fluorescent probes: a review and perspectives

Benzo[a]phenoxazine (BPO) based molecules have been recently emerged as a new class of near-infrared (NIR) fluorophore for image-guided diagnosis in cancer research. The successful application of BPOs as NIR fluorophore in biomedical research has led to explore their potential application in lipid-based staining, subcellular organelle profile labeling; bioimaging hypoxic tumor cells, and detection of small molecules. In this review, the development of novel NIR-activated fluorescent molecules based on BPO scaffold in cancer research are summarized and highlighted. BPOs are heterocyclic dye molecule consisting of an phenoxazine core with further elongation of another benzene ring fused along a-faces, which consists of freely electron donating and/or electron accepting substituents on BPOs core structure. The chemical synthesis and molecular design of these structures, unique optical, and photochemical properties are also discussed. We hope that this review will inspire and motivate research interest around BPO dyes and promote further development for the rational design of BPO-based fluorescent probes.