Discovery of asymmetric pyridinium-based fluorescent probes with large Stokes shifts for live neural stem/progenitor cells.

Fluorescent dyes are widely used in biological systems, yet the number of fluorescent scaffolds with desirable photophysical properties remains limited. Herein, we report the synthesis of novel asymmetric pyridinium salts via facile Rh(III) C-H activation. A structure-activity relationship (SAR) study led to the identification of a lead candidate, KD01, which exhibits a large Stokes shift (Ex/Em = 405/605 nm) and bright fluorescence only upon interaction with live brain cells. Remarkably, KD01 selectively labels undifferentiated human neural stem/progenitor cells (NSPCs) over differentiated neural cells. This selectivity is likely due to the probe's interaction with the unique biochemical or physical properties of the NSPC cytoplasm, such as binding to an abundant biomolecule. This work presents a bioactive fluorescent scaffold with unique optical properties and NSPC selectivity, offering a promising platform for live-cell imaging and targeted neural cell identification.