Dalton Transactions PAPER Cite this: DOI: 10.1039/c5dt04945h Received 20th December 2015, Accepted 25th January 2016 DOI: 10.1039/c5dt04945h www.rsc.org/dalton A highly selective, sensitive and reversible fluorescence chemosensor for Zn 2+ and its cell viability† Anoop Kumar Saini, a Mansi Srivastava, b Vinay Sharma, b Veenu Mishra a and Shaikh M. Mobin* a,b,c A new imine conjugate Schiff base ligand (H 2 L) was prepared and evaluated for its sensing properties. H 2 L detects Zn 2+ selectively among the wide range of metal ions. The sensing behavior of H 2 L was identified by UV-vis, fluorescence and 1 H NMR titration. H 2 L shows fluorescence switch ON with the Zn 2+ ion among 18 other metal/heavy metal ions with a detection limit of 1.47 μM. The binding of Zn 2+ was confirmed by single crystal X-ray studies, which reveal the formation of binuclear complex (1). The packing diagram of H 2 L reveals the presence of rare linear C–H⋯C interactions (bond distance 2.79 Å and bond angle 180°) which form 1D-polymeric chains. Furthermore, the cytotoxicity of H 2 L and 1 has been assessed against MCF-7 and A375 cell lines and both are found to have marginal toxicity. Introduction Zinc(II) is the second most abundant trace element found in the human body and is present as metalloproteins. 1–4 Zn 2+ plays a major role in various human diseases, such as Parkin- son’s disease, infantile diarrhea, Alzheimer’s disease, and ischemic stroke. 5–9 Compounds containing Zn 2+ have potential applications as tumor photosensitizers, antibacterials, anti- diabetics, insulin mimetics, and radioprotective and anticancer agents. 10 To monitor the movement and activity of Zn 2+ in the human body, the development of advanced detection methods involving fluorescence sensors and chemosensors are highly desirable. Due to the low cost, faster response time, and low detection limit with high selectivity and sensitivity, fluorescent chemosensors have recently gained considerable interest. 11–13 However, most of the presently reported Zn 2+ sensors suffer from some limitations like low signal continuity, high light scattering, auto-fluorescence and low Zn 2+ binding affinity. So far the fluorescence sensors synthesized for the selective detection of Zn 2+ contain some commonly used ligands such as fluorescein, coumarin, dipicolylamine, quinolone, and 4-nitrobenzoxadiazole as receptors in addition to their tedious reaction conditions. 14–17 On the other hand, simple Schiff base originated imine (HCvN−) group ligands are known for their metal binding affinity. 18–22 However, very few reports are available for the construction and design of a novel probe for Zn 2+ sensors. 23 Herein, we report the synthesis and sensing behavior of ligand H 2 L by using UV-visible, fluorescence and NMR titra- tion. The binding features of H 2 L towards Zn 2+ have also been discussed by using single crystal X-ray studies. The cytotoxicity associated with metal complexes is a key factor for their in vivo applicability; hence the cytotoxicity of H 2 L and 1 was also evaluated against MCF-7 and A375 cell lines. Results and discussion A new ligand 1,1′-(1E,1′E)-(2,4,6-trimethyl-1,3-phenylene)bis- (azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol (H 2 L) was obtained by the reaction of 2,4,6-trimethylbenzene- 1,3-diamine with 2-hydroxy-1-naphthaldehyde (1 : 2) in metha- nol under reflux conditions for 4 h (Scheme 1). H 2 L has been characterized by elemental analysis, NMR and ESI-MS spectro- scopic techniques and further authenticated by single crystal X-ray studies. H 2 L crystallizes in the monoclinic C2/c space group with a crystallographically imposed inversion center (Fig. 1 and Table 1). The central trimethyl benzene ring is observed to be slightly tilted from the plane by 2.87°, and the presence of two arms of 2-hydroxy-1-naphthyl moieties adjacent to each other † Electronic supplementary information (ESI) available. CCDC 1427927 and 1443306. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt04945h a Discipline of Chemistry, Indian Institute of Technology Indore, Simrol, Indore 452020, India b Centre for Biosciences and Bio-Medical Engineering, Indian Institute of Technology Indore, Simrol, Indore 452020, India c Centre for Material Science and Engineering, Indian Institute of Technology Indore, Simrol, Indore 452020, India. E-mail: xray@iiti.ac.in This journal is © The Royal Society of Chemistry 2016 Dalton Trans. Published on 25 January 2016. Downloaded by IIT Indore , Central Library on 02/02/2016 11:33:12. View Article Online View Journal