Spectrochimica Acta Part A 79 (2011) 370–375 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa 4-Salicylideneamino-3-methyl-1,2,4-triazole-5-thione as a sensor for aniline recognition M. Saravana Kumar, R. Tamilarasan, A. Sreekanth ∗ Department of Chemistry, National Institute of Technology – Tiruchirappalli, Tiruchirappalli 620015, Tamilnadu, India article info Article history: Received 2 December 2010 Received in revised form 2 March 2011 Accepted 11 March 2011 Keywords: Schiff base Sensor Aniline Benzene-1,4-diamine UV–visible spectroscopy 1 H NMR titration Photoluminescence abstract Tridentate triazole based Schiff base 4-salicylideneamino-3-methyl-1,2,4-triazole-5-thione has been found to selectively detect toxic aromatic amines such as aniline and benzene-1,4-diamine by simple titration techniques like UV–visible, fluorescence spectral studies (PL) and 1 H NMR titrations. The Schiff base receptor utilizes, thione sulfur, NH-thione and the phenolic hydroxyl group to form hydrogen bonded adduct of aniline and benzene-1,4-diamine with high binding affinity, followed by a slow removal of the corresponding hydrogens thus providing a promising candidate and an unique receptor for toxic aromatic amines. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Most of the aromatic amines are found to be toxic in humans leading to bladder cancer when inhaled [1]. Aniline is one of the most toxic among the aromatic amine family, but has a wide spread application as a precursor to more complex chemicals. The toxic- ity of aniline and similar types of compounds on humans is well documented [2,3], with an oral lethal dose being 50–500 mg/kg for a grown man. The primary toxicity of aniline is characterized by methemoglobinemia; the increased production of methemoglobin can cause interference with the oxygen-carrying capacity of the blood. Despite its structural simplicity, the metabolism of aniline is complex and hence it is important to find out a good receptor to sense the aniline. Only few synthetic receptors have been developed in the recent past due to the challenge in binding of the guest molecule (ani- line) with the synthetic receptors developed. Such systems are generally composed of anion binding sites and the chromogenic moieties. When anions interact with the sensor via electrostatic, hydrogen bonding, coordination to a metal center, hydrophobic interaction, or a combination of any two or more of these inter- actions, the sensor can output binding information either by its altered behavior in fluorescence or in absorption spectra [4,5]. Li et al., have used 2,6-Bis(2-benzimidazolyl)pyridine and showed it ∗ Corresponding author. Tel.: +91 431 2503642; fax: +91 431 2500133. E-mail addresses: sreekanth@nitt.edu, sreekanth a@yahoo.com (A. Sreekanth). to be an efficient receptor for binding aniline with high affinity [6]. It is observed that the host–guest complex formed between the 2,6-Bis(2-benzimidazolyl)pyridine and aniline is very stable, where 2,6-Bis(2-benzimidazolyl)pyridine utilizes not only its cav- ity but also the imine nitrogen located on the outer core to form a stable complex. Encouraged by this, we investigated the sensing behavior of 4-salicylideneamino-3-methyl-1,2,4-triazole-5-thione [7] against aniline and benzene-1,4-diamine. There are only few reports on aniline sensors and Schiff base functioning as aniline receptor has not been found anywhere in the literature. 2. Experimental 2.1. Materials and methods Thiocarbohydrazide, glacial acetic acid, salicylaldehyde, ani- line (G1) and benzene-1,4-diamine (G2) were purchased from Aldrich Chemicals and were used without further purification. 4- Salicylideneamino-3-methyl-1,2,4-triazole-5-thione and 4-amino- 3-methyl-1,2,4-triazole-5-thione was synthesized according to the literature methods [7,8]. Acetonitrile was purified using the standard procedure. Titration of the receptor molecule 4-salicylideneamino-3-methyl-1,2,4-triazole-5-thione (receptor) with the guest molecules was performed cautiously by careful addi- tions of G1 aliquots in to the acetonitrile solution of the receptor. The ratios of receptor/G1 and receptor/G2 are given as follows, A: pure receptor (1 × 10 -5 mol/L); B: 1:0.2 (1 × 10 -5 mol/L:0.2 × 10 -5 mol/L); C: 1:0.4 (1 × 10 -5 mol/L:0.4 × 10 -5 mol/L); D: 1:0.6 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.03.030