Controllable Coumarin-Based NIR Fluorophores: Selective Subcellular Imaging, Cell Membrane Potential Indication, and Enhanced Photodynamic Therapy

Fluorescent materials with advanced functionalities provide powerful tools to visualize subcellular microstructures and monitor subcellular dynamic functions, which significantly boost our understanding of complex biological phenomena and manipulation of biological behaviors. However, realization of diverse biological applications from a single molecular backbone is still a challenging endeavor. In this contribution, a series of coumarin-based cationic fluorophores (Cou-n, n = 1–4) with near-infrared emission (675 nm) and large Stokes shifts (110 nm) have been developed. Considering their excellent biocompatibilities and alkyl chain-dependent lipophilicities, Cou-1 and Cou-3 could selectively and ultrafast (<30 s) stain the cell plasma membrane and mitochondria in a washing-free manner, respectively. Meanwhile, Cou-1 could sensitively respond to the change of the plasma membrane potential, which enabled Cou-1 to successfully indicate the cell passage number. Taking advantage of specific mitochondria targeting as well as efficient singlet oxygen generation, Cou-3 exhibited enhanced photodynamic therapy (PDT) effect for tumor inhibition in vivo. In addition, the suitable lipophilicity of Cou-3 aided it in selectively imaging Gram-positive bacteria and efficiently killing bacteria by the PDT process.