Fluorogenic ratiometric dipodal optode containing imine-amide linkages: Exploiting subtle thorium (IV) ion sensing Kundan Tayade a , Amanpreet Kaur b , Sandesh Tetgure a , G. Krishana Chaitanya c , Narinder Singh d , Anil Kuwar a, * a School of Chemical Sciences, North Maharashtra University, Jalgaon, India b Centre for Nanoscience and Nanotechnology, Panjab University, Chandigarh, India c School of Chemical Sciences, Swami Ramanand Tirth Marathawada University, Nanded, India d Department of Chemistry, Indian Institute of Technology, Ropar, Punjab, India H I G H L I G H T S G R A P H I C A L A B S T R A C T  A highly selective, simple, noncyclic, imine-amide based dipodal off–on fluorescence chemosensor for Th 4+ ion is reported.  Sensing mechanism is based upon twisted plane intramolecular charge–transfer upon interaction with cations.  Th 4+ ion on detection limit (as low as 0.1 mM) is reported.  This system can also be applied in real samples. A R T I C L E I N F O Article history: Received 12 June 2014 Received in revised form 8 September 2014 Accepted 10 September 2014 Available online 16 September 2014 Keywords: Ratiometric fluorescent sensor Tetravalent thorium ion (Th 4+ ) Real sample analysis A B S T R A C T The (13E,19E)-N1 0 ,N3 0 -bis[4-(diethylamino)-2-hydroxybenzylidene]malonohydrazide (L) has been de- veloped for the detection of Th 4+ ions using dual channel signalling system. The UV–vis absorbance and fluorescence spectroscopic data revealed the formation of L–Th 4+ complex in 1:1 equilibrium. The density functional theory (DFT) also confirms the optimum binding cavity for the recognition of metal ion. The binding constant computed from different mathematical models for an assembly of L–Th 4+ . The detection limit of L for Th 4+ recognition is to a concentration down to 0.1 mM (0.023 mg g 1 ). The present sensing system is also successfully applied for the detection of Th 4+ ion present in soil near nuclear atomic plants. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction The supramolecular motifs are on the verge of getting transformed towards approaches involving architecture and application of selective as well as sensitive fluorescent and/or colorimetric sensors for physiologically important and hazardous metal ions belonging to transition series and post transition series elements [1–5]. The interest in the development of sensors is due to the apprehension related to perilous effect of these ions on the environment and also due to their adverse effects on physiologi- cal processes when they exceed the cellular needs [6–9]. The reported sensors reveals that now a day noncyclic compounds having array of binding sites for noncovalent interactions are converging for complexation towards respective cationic/anionic * Corresponding author. Tel.: +91 2572257403. E-mail addresses: kuwaras@gmail.com, kuwaras@rediffmail.com (A. Kuwar). http://dx.doi.org/10.1016/j.aca.2014.09.016 0003-2670/ ã 2014 Elsevier B.V. All rights reserved. Analytica Chimica Acta 852 (2014) 196–202 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepa ge: www.elsev ier.com/locate /aca