An NIR-emitting lysosome-targeting probe with large Stokes shift via coupling cyanine and excited-state intramolecular proton transfer

An NIR-emitting probe (lambda(em) similar to 700 nm) with a large Stokes shift (Delta lambda approximate to 234 nm) is synthesized by using excited-state intramolecular proton transfer (ESIPT). The phenolic proton, which controls ESIPT, acts as a switch to give strong fluorescence at pH approximate to 5. The probe can selectively show lysosome organelles, therefore leading to a lysosome probe without exhibiting an alkalinizing effect''.