Azacrown indoaniline dye as a sensing molecule in optical sensors for the selective detection of Li + Sung-Hoon Kim a, *, Jae-Woo Kim a , Jae-Ho Kim b , Kwang-Nak Koh c , Shin-Won Kang c a Department of Dyeing and Finishing, College of Engineering, Kyungpook National University, Taegu 702-701, South Korea b Department of Molecular Science and Technology, Ajou University, Suwon 442-749, South Korea c Sensor Technology Research Center, Kyungpook National University, Taegu 702-701, South Korea Received 28 January 2000; received in revised form 18 February 2000; accepted 29 March 2000 Abstract The complex formation of azacrown indoaniline (ACIA) dye 9 with Li + and Na + was investigated spectro- photometrically. As the polarity of the solvent decreased, the complexation ability increased. ACIA 9 exhibits higher Li + selectivity than Na + ion in CH 2 Cl 2 ±CH 3 CN. The speci®c spectral response to Li + ion by ACIA 9 indicates potential suitability for optical sensor applications. # 2000 Published by Elsevier Science Ltd. All rights reserved. Keywords: Indoaniline dye; Azacrown; Optical sensor; Chromophore; MM2; Solvent polarity 1. Introduction Selective ion carriers have been of considerable interest as tools for the analysis and separation of metal ions as well as for many biological applica- tions. Expanding applications in science, medicine, and technology have led to increased interest in lithium and its compound [1]. Lithium salts have been used in the treatment of manic depression and other neurological and psy- chiatric disorders [2]. In light of such applications, methodology for the separation and determination of Li + is receiving considerable attention. Iono- phores for divalent cations and some alkali metal ions are well known [3,4] but so far few carriers speci®c for Li + have been described. The design of ionophores for Li + is a dicult problem owing to the fact that lithium ions are smaller than both sodium and potassium ions but are strongly hydrated in aqueous solution [5], and hence few lithium ionophores have been synthesized. Exam- ples of selective ligands for lithium ions relative to sodium ion are the macrocyclic crown ethers [6], cryptands [7], spherands [8] and acyclic diamides [9], which have achieved remarkable binding selec- tivity. Some tetraaza macrocycles related to por- phyrins and phthalocyanines [10], acyclic polyethers [11], and jasplakinolide [12], the only known lithium ionophores, have also been synthesized or isolated. Selective chromogenic reagents, alone or in combi- nation with a masking agent, have satisfactorily been used for the colorimetric determination of 0143-7208/00/$ - see front matter # 2000 Published by Elsevier Science Ltd. All rights reserved. PII: S0143-7208(00)00028-0 Dyes and Pigments 46 (2000) 49±53 * Corresponding author. Tel.: +82-53-950-5641; fax: +82- 53-950-6617. E-mail address: shokim@bh.kyungpook.ac.kr (S.-H. Kim).