Spectrochimica Acta Part A 79 (2011) 1352–1355 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy jou rn al hom epa ge: www.elsevier.com/locate/saa A novel fluoride ion colorimetric chemosensor based on coumarin Xiaoqing Zhuang, Weimin Liu ∗ , Jiasheng Wu, Hongyan Zhang, Pengfei Wang Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China a r t i c l e i n f o Article history: Received 22 March 2011 Received in revised form 15 April 2011 Accepted 27 April 2011 Keywords: Colorimetric chemosensor Anion recognition Fluoride sensing Coumarin Schiff base a b s t r a c t A novel visible colorimetric sensor (L 1 ) with high selectivity for fluoride ion based on coumarin has been synthesized by a simple modification of our earlier report. The chemosensor L 1 shows an obvious color change from yellow to blue upon addition of fluoride ion with a large red shift of 145 nm in acetonitrile, and without interference of other anions such as Cl - , Br - , I - , NO 3 - , H 2 PO 4 - , HSO 4 - , and AcO - . The investigation of 1 H NMR spectrum titration indicates the proposed mechanism is that F - first establishes a hydrogen bonding interaction with L 1 , and then the formation of [F–H–F] - induces deprotonation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Anion recognition is an important issue in supramolecular chemistry as anions play a significant role in chemistry industry, biochemistry, and environmental science [1,2]. As the first anion in the periodic table of elements, fluoride ion has unique biology and chemistry properties. It is an essential trace element in human and shortage of fluoride results in dental caries and osteoporosis. In many countries, fluoride has been added to water widespread to prevent tooth decay. However, high dose or chronic ingestion of lower doses of fluoride may result in fluorosis, and lead to nephro- toxic changes and urolithiasis in humans [3–8]. In addition, with the development of industry and the increase in the number and the scale of enterprises on fluorine products, the contamination of fluo- rine becomes more serious. For these reasons, selective recognition of fluorine ion is of realistic significance. In recent years, many analytical methods have been devel- oped for fluoride ion detection. Among all the analysis methods, colorimetry, known as naked eye detection, has attracted much attention due to its rather straightforward and fast measurement protocols and no need of valuable instruments [9,10,2,11–13]. These methods are mostly based on N–H proton transfer from the donor unit to fluoride ion, which induced -electron delocalization, or N–H deprotonation [14]. The hydrogen donator includes amine [15], amide [16], pyrrole [17,18], and urea [19–21]. However, highly basic anions such as CH 3 CO 2 - or H 2 PO 4 - can also act as an acceptor, and cause similar spectral changes with fluoride ion [22,23]. There- ∗ Corresponding author. Tel.: +86 10 82543475; fax: +86 10 82543475. E-mail address: wmliu@mail.ipc.ac.cn (W. Liu). fore, there is a great challenge to construct the colorimetric sensor with specific receptor for the fluoride ion and suitable chromophore for obvious color change. Up to now, the colorimetric sensors based on N–H proton transfer that satisfy the above conditions are rarely reported. Present study is a part of our current research interest towards chemosensors based on coumarin with Schiff base (–C N–) as bridge [24–26]. The present chemoreceptor in this work is a simple structural modification of one of our earlier report [27]. This modi- fication was worthwhile to modulate the acidity of N–H proton by decreasing the numbers of nitro-group, so that the new receptor can be able to discriminate between anions of high and compa- rable basicity like fluoride and dihydrogen phosphate. Compound L 1 was designed and synthesized by the condensation of 7-N,N- diethyl-aminocoumarin and 4-nitrophenylhydrazine (Scheme 1). The result shows that the fluoride ion could be detected by naked eyes without interference from other anions. The details of anion binding characteristics of the compound L 1 have been investigated by UV–vis and 1 H NMR titrations. The maximum of absorption of L 1 shifts 145 nm in the presence of the fluoride ion in CH 3 CN solution due to the N–H deprotonation and formation of the particularly stable [F–H–F] - dimer. 2. Experimental 2.1. Reagents and instruments 7-(Diethylamino)-2-oxo-2H-chromene-3-carbaldehyde was synthesized according to reported methods [24]. 4- nitrophenylhydrazine hydrochloride and all anions were purchased from Sigma Aldrich and used without any further 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.04.068