2286 | Mater. Chem. Front., 2018, 2, 2286--2296 This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2018 Cite this: Mater. Chem. Front., 2018, 2, 2286 Cholesterol-based diazine derivative: selective sensing of Ag + and Fe 3+ ions through gelation and the performance of metallogels in dye and picric acid adsorption from water† Atanu Panja and Kumaresh Ghosh * Cholesterol appended diazine derivative 1 on a 4-hydroxybenzaldehyde scaffold has been designed and synthesized. The compound having diazine as a metal ion binding site forms nice gels with Ag + and Fe 3+ ions over a series of other metal ions from CHCl 3 /CH 3 OH (3 : 1, v/v). Strong hydrophobic interaction owing to the presence of cholesterol has a marked contribution in aggregation. The SEM image reveals fibrillar to globular porous microstructures. The true nature of the gels is determined from a rheological study. The Ag + and Fe 3+ -gels are distinguishable with the aid of tetrabutylammonium chloride, tetrabutylammonium bromide or fluoride and ammonium thiocyanate. There is no interference of Fe 2+ ions in the detection of Fe 3+ ions. The presence of Fe 2+ ions in solution can successfully be ascertained through gelation of 1 in the specified solvent upon adding external oxidising agents such as m-CPBA. As an application, both the Ag + - and Fe 3+ -gels of 1 act as good adsorbents for adsorption of uranine dye and picric acid from aqueous solution. In this process, the metallogels are recyclable and exhibit excellent efficiency. Introduction Selective sensing and visualization of biologically significant analytes through prolific use of low molecular weight supra- molecular gelators (LMWGs) have become an ongoing research interest in recent times. 1 Low molecular weight supramolecular gelators (LMWGs) under weak noncovalent forces establish a cross-linked network in solution due to which gel formation occurs. 2 The self-organization of such gelator molecules can be tuned by regulating the weak forces using external physical or chemical stimuli (light, redox, pH, ions). 3 Chemical stimuli- induced changes in gel properties are beneficial for the develop- ment of new molecular sensors. 1–3 In continuation of our ongoing research interest in develop- ing stimuli responsive supramolecular gelators on a 4-hydroxy- benzaldehyde–cholesterol platform, 4 we herein wish to report a simple, easy to make diazine functionalized LMWG 1 which performs excellently in metal ion sensing with practical applications. The hydrazine-based dipodal symmetrical imines (1,4-disustituted azines or diazines) are well known metal chelators and they are successfully used in various colorimetric and fluorescent sensors. 5 This class of ligands possess delocal- ized electron density on the C Q N–N Q C bond. Binding of metal ions to the diazine motif restricts the free rotation of the N–N bond and displays optical feedback. Compounds with this functionality are also known to exhibit interesting properties like excited state intramolecular proton transfer (ESIPT), aggregation induced emission enhancement (AIEE) etc. 5g Considering all these properties, the designed compound 1 was selected which formed nice gels from a CHCl 3 /CH 3 OH mixture solvent in the presence of Ag + and Fe 3+ ions. The metallogels have applications in various aspects. Here, they are established to be useful in discrimination of halides, dye adsorption and picric acid removal from waste water. Fig. 1 represents the different components of gelator 1. While the cholesterol motif has been introduced for assisting self- aggregation of the molecules through hydrophobic interaction, 6 the diazine bridge is used as the site of metal ion interaction with an expectation of influencing the gelation property of compound 1 (either gel-to-sol or vice versa). Moreover, the use of a large hydrophobic surface in the design has a discernible impact on dye adsorption in the aggregated state. 1g,4c Among the different analytes, sensing and detection of Ag + and Fe 3+ ions draw much attention because of their biological significance. 7 Although, Ag + ions have broad applications in Department of Chemistry, University of Kalyani, Kalyani-741235, India. E-mail: ghosh_k2003@yahoo.co.in, kumareshchem18@klyuniv.ac.in; Fax: +91-3325828282; Tel: +91-3325828750 ext. 305 † Electronic supplementary information (ESI) available: Figures showing the gelation profile, gel pics, FTIR data, UV-vis titration plots of 1 with various metal ions, binding constant and detection limit plots and other spectral plots, comparison table, and characterization spectra. See DOI: 10.1039/c8qm00433a Received 28th August 2018, Accepted 4th October 2018 DOI: 10.1039/c8qm00433a rsc.li/frontiers-materials MATERIALS CHEMISTRY FRONTIERS RESEARCH ARTICLE Published on 04 October 2018. Downloaded on 1/14/2023 4:20:32 PM. View Article Online View Journal | View Issue