Synthesizing Red Fluorescent Carbon Dots from Rigid Polycyclic Conjugated Molecules: Dual‐Mode Sensing and Bioimaging in Biochemical Applications

Abstract Red fluorescent carbon dots (R‐CDs) are special desirable for biochemical analysis due to good biological compatibility and deep penetration; however, they remain as bottlenecks due to difficulties in expanding the sp 2 domain, especially those are fused from rigid polycyclic conjugated molecules (RPCMs) with heteroatom substituents due to huge steric hindrance and heteroatom blockage toward graphic lattice. Here, an RPCM with heteroatom substituents, 1,5‐diamino‐4,8‐dihydroxyanthraquinone (DDAQ), based self‐doped R‐CDs with PL emission at 635 nm is reported. Further investigations reveal that the expanding, hybrid sp 2 domain with indanthrone tannin structure from DDAQ is mainly responsible for the obtained red fluorescence of R‐CDs. Taking advantage of optical properties, R‐CDs are considered to construct a colorimetric/fluorescent dual mode sensing array for quantifying trace levels of Fe 3+ and glyphosate based on the static quenching, and a biomarker for cell imaging. The CD‐based sensors exhibit outstanding recovery, high selectivity, and sensitivity, also facilitated dual‐mode detection with the naked‐eye. The R‐CDs have low cytotoxicity, good cell membrane penetration for rapid cell entry, and high resolution, demonstrating their potential for biolabeling and bioanalytic applications.