Reconsideration of the ESIPT off mechanism for fluorescent probe MNC in aqueous solution

Fluorescent probes with excited state intramolecular proton transfer (ESIPT) properties play a significant role in the research of life science and material science. Guo et al. designed 3-hydroxy-2-(6-Methoxynaphthalen-2-yl)4H-chromen-4-one (MNC) as a control to achieve the dual-color fluorescence imaging of lipid droplets and endoplasmic reticulum (ER). They deemed that the ESIPT process would be turned off in ER with high water content [J. Am. Chem. Soc. 2021, 143, 3169-3179]. However, contrary to the conventional ESIPT off case, the enol* state fluorescence intensity that should have been enhanced was severely quenched in water. Here, combined with ultrafast spectrum, steady-state fluorescence spectrum and potential energy surface, the mechanism of ESIPT process of MNC turned off in water is revised. Furthermore, the formation of aggregated states in

Automated summary

Fluorescent probes with excited state intramolecular proton transfer (ESIPT) properties are crucial in life science and material science research. Guo et al. designed a control compound, 3-hydroxy-2-(6-Methoxynaphthalen-2-yl)4H-chromen-4-one (MNC), for dual-color fluorescence imaging of lipid droplets and endoplasmic reticulum (ER). They expected the ESIPT process to be turned off in ER with high water content. However, contrary to expectations, the fluorescence intensity of the enol* state in water was severely quenched. By utilizing ultrafast spectrum, steady-state fluorescence spectrum, and potential energy surface, the mechanism of the ESIPT process of MNC turning off in water was revised, and the importance of aggregated states formation was highlighted.