Large Stokes shift by increasing intramolecular charge transfer for high signal-to-background ratio bioimaging

Novel bicyclic 2-pyridone probes with strong electron donors (from Br in cDHIP-N-Br to dimethoxytriphenylamine in cDHIP-N-MTPA) exhibit redshifted emission (535-759 nm) and large Stokes shifts (≤320 nm) due to ICT effects, enabling high-contrast bioimaging in cells, tumor spheroids, and mice, showcasing their potential for advanced fluorescence imaging.