Short communication Synthesis and characterisation of crown ether based azo dyes B.R. Pandya, Y.K. Agrawal* Chemistry Department, School of Sciences, Gujarat University, Ahmedabad 380 009, India Received 9 November 2000; received in revised form 21 March 2001; accepted 11 September 2001 Abstract Five new azo dyes derived from trans-diaminodibenzo-18-crown-6-ether have been synthesised. The physico-chemical properties and the application of these dyes on cotton fiber are discussed, and results from dye evaluations in paints and inks are presented. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Crown ethers; Azo dyes; Physico-chemical properties 1. Introduction Macrocyclic compounds are commonly used in phase transfer reactions, biomimetic studies, and as specific and selective complexing agents for metals. Recently, crown ether derivatives with ethereal or anionic groups on the periphery of the macrocycles have been developed, in order to increase metal selectivity and complex stability in analytical and separation methods as well as in biological mem- branes [1–7]. Several workers have reported modified crown ethers with chromogenic groups [8–11] and it is known that varying the size of the crown ether ring or the chromophoric side arm can modify the prop- erties of these compounds. Such changes produce agents with different sensitivities and selectivities for metal ions, including crown ether based dyes pos- sessing a potential anionic site attached to the chromophore [12]. These structures form inter- molecular ion-pair complexes with various metal cations [12]. Other types of crown ether dyes are those that do not contain ionic groups in the vicinity of the chromophore. The color value of both types of crown ether dyes is influenced con- siderably by the size of the crown ether cavity, the complexed metal cations, and the charge density of the cation. Thus, crown ether derivatives bearing chromophores are promising analytical reagents for colorimetry and metal ion indicators. Considerable attention has been focused on crown ether dyes containing a chromophore such as picrylamine (I; Fig. 1) [13,14] that can be used for photometric determination of alkali and alka- line earth metal ions. Azo dyes such as the p- dimethylaniline-based crown dyes (II; Fig. 1) [15– 19] have also been employed for complexing alkali and alkaline earth metal ions. Generally, dyes with styryl functional groups (cf. III) exhibit cis–trans photoisomerization [20,21]. The synthesis of crown ether based azo dyes in which an aniline derivative was diazotized and coupled with a phenol residue in a crown ether moiety (cf. IV) has also been reported [22]. In other studies, Shinkai and co- workers have synthesized a variety of bis-(crown 0143-7208/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0143-7208(01)00069-9 Dyes and Pigments 52 (2002) 161–168 www.elsevier.com/locate/dyepig * Corresponding author. Tel.: +91-76-63-00969; fax: +91- 79-63-08545.