Currently, heavy metal ion pollution is surpassing the threshold limits in various areas of the world due to the growth of industrialization and modernization, for example, coal, and gold mining , oil refining , and paint production . In comparison to other heavy metal ions, mercury (Hg2+) is the utmost toxic metal pollutant due to its assorted utilisation in numerous industries and horticultural sciences [4, 5]. Non-biodegradable mercury ion prompts extreme tainting of marine resources and soil. Besides, Hg2+ gets aggregated in rural and sea-going effluence [6, 7] and causes serious medical and environmental problems, named as myocardial localized necrosis, chemical imbalance, and Minamata sickness [8–11]. As an attempt to ensure human wellbeing, the United States Environmental Protection Agency (USEPA) has proclaimed the Hg2+ ion threshold limit value (TLV) in drinking water sources as 2 ppb [12, 13]. In view of, ecological and medical problems related to Hg2+, it is exceptionally fundamental to progress a solid sensing strategy with high sensitivity for observing low levels of Hg2+ in the environment and biological systems.
Various analytical techniques like electrochemical methods , atomic absorption spectroscopy (AAS) , inductively coupled plasma spectroscopy (ICPS) , and colorimetry  have been used for the detection of various heavy metals. The abovementioned analytical techniques need sophisticated and expensive instruments, tedious preparation, and also pre-treatment of the sample. Among them, the spectrofluorimetric technique has attracted much attention due to its facile and effective method of detecting chemical and biological species, high sensitivity, selectivity, quick response, cost-effectiveness, simplicity and a need of low concentration of analytes . Supramolecular IC has gained more attention compared to other fluorophores like coumarin, pyrene and xanthene derivatives, metallic organic frameworks etc., Supramolecular Inclusion complexes were better and preferable fluorogenic probes for sensing the analytes due to their advantages in selectivity, sensitivity, easy sample preparation, real-time analysis.
Cyclodextrin (CD) belong to the family of cyclic oligosaccharides. It is also known as Schrodinger dextrin’s, cycloamyloses and cyclomaltoses. It consists of a macrocyclic ring of glucose subunits joined by α-1,4 glycosidic bonds. Cyclodextrins are obtained from enzymatic hydrolysis of starch. The β-cyclodextrin is a natural oligomer, which has a hydrophobic cavity and an exterior which is highly hydrophilic in nature. The cyclodextrin’s hydrophobic interior surface is torus-shaped structure, which permits guest molecules naturally into the hydrophobic cavity by expelling the molecules of water . The cyclodextrins have the ability to form host-guest complex molecule which leads to a number of advantages in different fields [20, 21]. These cyclodextrins (CDs) have been used in number of industries such as pharmaceutical, food, analytical and catalysis. These CDs acts a solubilizers, diluents, tablet ingredients to enhance the solubility, chemical stability, pharma kinetic properties, and bioavailability of drugs . Hydroxypropyl-beta-cyclodextrin (H-CD) is hydrophilic in nature, and considered as a toxic-free derivative at oral and intravenous doses. Recently, H-CD used to increase the stability, solubility and bio-availability of poorly solvable compounds in drug delivery .
Acetylphenyl-4-(((6-chlorobenzo[d]thiazol-2-yl)-imino)-methyl)-benzoate (compound L), a crystalline solid is a polycyclic aromatic compound. Compound (L) acts as a fluorescent sensor in a hydrophilic environment. But it exhibits strong fluorescence in the hydrophobic cyclodextrin cavity. It easily binds with mercury metal ions and enhances the fluorescence intensity. In addition, compound (L) has a major role as a fluorescent probe in life cell imaging and real sample analysis. This compound is encapsulated into the H-CD hydrophobic cavity with the release of water molecules.
The key area of the present work is to synthesize H-CD/L solid IC under reflux condition for sensing metal cation. The obtained experimental results showed that the solid IC selectively and sensitively sense mercury metal ion (Hg2+) and it was observed through a visible colour change, absorption and fluorescence spectrum. Based on this phenomenon, a new supramolecular sensor (H-CD: L) has been synthesised by using compound L with H-CD and its more effective in photoluminescence (PL) sensing towards Hg2+. The H-CD: L solid IC shown considerable color variation, PL enhancement upon the addition of Hg2+, which might be used in absorbance and PL sensing for Hg2+ in liquid medium. The H-CD: L solid IC could also be applied for real sample analysis and life cell imaging.