Colorimetric as well as dual switching fluorescence ‘turn on’ chemosensors for exclusive recognition of Zn 2+ and HSO -- 4 in aqueous solution: experimental and theoretical studies Shyamaprosad Goswami a,⇑ , Sangita Das a , Krishnendu Aich a , Deblina Sarkar b , Tapan Kumar Mondal b a Department of Chemistry, Bengal Engg. and Science University, Shibpur, Howrah 711103, India b Department of Chemistry, Jadavpur University, Kolkata 700032, India article info Article history: Received 2 July 2013 Revised 7 October 2013 Accepted 8 October 2013 Available online 14 October 2013 Keywords: Sensor Colorimetric and fluorometric Zn 2+ HSO À 4 DFT abstract In this Letter, we have designed and synthesized two salicylaldehyde based probes (DPSH and ANSH) which selectively detect Zn 2+ and HSO À 4 over other physiologically and environmentally important ions with a fluorescence enhancement at two different wavelengths in aqueous acetonitrile solution. The binding mode and change of electronic properties of DPSH and ANSH with Zn 2+ and HSO À 4 were modeled by DFT (density functional theory) and TDDFT (time dependent density functional theory) computational calculations, respectively. The minimum limits of detection (LOD) of the sensors with both cases were in the order of 10 À8 M each. Ó 2013 Elsevier Ltd. All rights reserved. The ability of photochromic compounds to recognize and re- spond to a range of external stimuli has resulted in an increasing number of studies that focus on their design and synthesis. The photoinduced switching characteristics of such compounds give them tremendous potential in molecular electronics and sensor de- vice fabrication. 1 Recently chemosensors based on the ion-induced fluorescence changes have become increasingly popular due to their simplicity, high sensitivity, and selectivity. 2 Transition metal ions are an interesting paradox in life. 3 They can be both integral enzyme components necessary for biological activity 4 and toxic to human life, flora, and fauna. Zinc is the second most abundant transition metal ion after Fe 2+ or Fe 3+ in humans and other mam- mals. 5 Recently, fluorescent chemosensors for zinc ions have re- ceived wide attention due to the vital roles played by zinc in numerous biological processes, including catalytic activity, brain activity, gene transcription, immune function, and cellular trans- port. 6,7 The unregulated zinc level in the body may lead to a num- ber of severe neurological diseases, developmental defects, and malfunctions. 8–10 Furthermore, detection of zinc is also important for environmental safety as zinc is a harmful metal pollutant to the environment. 11 Thus, intensive efforts have been devoted to develop sensitive fluorescence sensors for detection of trace amounts of zinc ions both ‘in vitro’ and ‘in vivo’ and a variety of chemosensors for zinc have been reported in the past years. 12 However, most of them suffer from a turn off response, low detec- tion limit, low water solubility and cross sensitivity toward other heavy metal ions. Therefore, it remains a challenging task to devel- op a sensitive chemosensor for Zn 2+ ions with fluorescence enhancement exhibiting a high selectivity and sensitivity for Zn 2+ over other metal ions. On the other hand, the development of sul- fate selective anion receptors is currently an area of intense inter- est due to the important role this anion plays in biological system and disease 13 and the appreciation of the role they could play in radioactive waste remediation. 14 Among the various anions, hydro- gen sulfate (HSO À 4 ) ions dissociate at high pH to generate toxic sul- fate (SO 2À 4 ) causing irritation of the skin and eyes and even respiratory paralysis. Despite its crucial roles in biological pro- cesses, only a few sensors for HSO À 4 have been reported to date. 15 Consequently, one of the current challenges in anion recognition chemistry involves the preparation of receptors that show high sulfate selectivity. 16 So far there have been a large number of sen- sors based on detection of Zn 2+ , but only a few fluorescent water soluble HSO À 4 sensors have been reported. 15c,d,h Treatment of 4,4 0 - diaminodiphenylmethane with 4-(diethylamino) salicylaldehyde in ethanol medium afforded the probe (DPSH) as yellow powder in 94% yield (Scheme 1). Another probe (ANSH) was prepared by using aniline and 4-(diethylamino) salicylaldehyde in ethanol with 90% yield (detailed procedures are given in Supplementary data). Both receptors are characterized by 1 H NMR, 13 C NMR, and HRMS. 0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tetlet.2013.10.033 ⇑ Corresponding author. Tel.: +91 33 2668 2961–3; fax: +91 33 2668 2916. E-mail address: spgoswamical@yahoo.com (S. Goswami). Tetrahedron Letters 54 (2013) 6892–6896 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet