High efficiency detection of Zn2+ through the improved electron density of aromatic π-conjugated bridges

Zinc ions (Zn 2+ ) play a crucial role in maintaining human health, and their imbalance has been associated with various diseases and environmental contamination. Although many fluorescent probes have been developed for Zn 2+ detection, they often face challenges, including short emission wavelengths, narrow Stokes shifts, and particularly the poor selectivity. Here, aromatic rings with different electron densities including benzene, thiophene and furan rings, were introduced as aromatic π -conjugated bridges to connect dicyanoisophorone (DCI) and amide-di-2-picolylamine (DPA) based structures, and three probes L1, L2 and L3 for Zn 2+ detection were developed. Our results demonstrated that compared with L1, L2 and L3 , which inserting thiophene and furan rings, revealed near-infrared (NIR) emission at 651 nm, and a larger Stokes shift of 187 nm. Notably, different from L2, L3 , which incorporated a furan ring with the highest electron density, exhibited the highest selectivity for Zn 2+ with a low detection limit of 31 nmol/L. In addition, the binding mode of L3 with Zn 2+ was confirmed in the form of an imidic acid tautomer. Furthermore, L3 was successfully applied in cellular imaging, validating its potential for in vivo bioimaging. This study presents a promising strategy for developing high-performance Zn 2+ probes by simply modifying the aromatic π -conjugated bridges. This study presents a promising strategy for developing NIR fluorescent probes with high selectivity for Zn 2+ detection through a simple enhancement of the electron density of the aromatic π -conjugated bridge.