A unique rectilinearly π-extended rhodamine dye with large Stokes shift and near-infrared fluorescence for bioimaging.

The synthesis of a novel rectilinearly π-extended rhodamine dye (TJ730) has been described. It exhibits NIR fluorescence emission with a Stokes shift of >110 nm. TJ730 and its ester derivative are cell permeable, have low cytotoxicity, are biocompatible, and can be directly used as NIR tracers for lysosome staining. Using TJ730 as a precursor, two probes have been prepared for Cu ²⁺ .