A Step Toward an NIR-Emitting ESIPT Probe for Smart Zn²⁺ Sensing in Different Environments

Current sensors for Zn²⁺ detection are largely based on the photoinduced electron transfer (PET) mechanism, which can effectively change the fluorescence intensity, without inducing a significant spectral shift. By coupling the PET mechanism with an excited state intramolecular proton transfer (ESIPT), a near-infrared fluorescent sensor was developed for Zn²⁺ detection. Upon binding to the Zn²⁺ cation, the sensor was able to generate two well-separated emission bands (λ_em ≈ 540 and 770 nm), whose ratio was quite sensitive to the probe's environments. The finding offers an advanced tool for in vitro and in vivo imaging of the Zn²⁺ cation, which is desirable for future discovery of the biological functions of zinc.