Small molecular N-heteroaromatic-based optical sensing of noxious Hg ions: comprehensive insights into recent advancements, existing challenges, and future perspectives.

Hg ions are very toxic to the surrounding ecology and extant mammalian health and can damage the ecosystem even at a trace concentration level. Exposure to mercury can induce severe adverse effects on the human respiratory system and central nervous system (CNS), and it can cause skin damage, kidney failure, and various mental disorders. Therefore, the detection and estimation of Hg ions using alternative novel techniques are crucial as traditional methods require expensive equipment and skilled personnel. Owing to their high sensitivity and selectivity, optical sensors have attracted significant attention for the sensitive and selective detection of various toxic environmental species. Recently, small molecular probes with N-heterocyclic fluorophoric receptors have successfully been utilized in different sensing fields owing to their cost-effective synthesis and commendable photophysical activities. In the last fifteen years, numerous research groups have reported various N-heterocyclic-based receptors for sensing Hg ions in the solution and solid states with excellent selectivity, sensitivity, and reversibility and a low limit of detection in real-world applications. Thus, this review aims to provide the current progress and future viewpoints in N-heteroaromatic-based colorimetric and/or fluorogenic Hg ion sensors with wide real-time applications.