Highly Sensitive and Selective Fluoride Ion Chemosensing, Fluoroalkylated Polysilane a Anubhav Saxena, 1,2 Michiya Fujiki,* 1,2 Roopali Rai, 1,2 Sun-Young Kim, 1 Giseop Kwak 1,2 1 Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan Fax: (þ81) 743-72-6049; E-mail: fujikim@ms.naist.jp 2 CREST-JST (Japan Science and Technology Agency), 4-1-8 Hon-cho, Kawaguchi, Saitama 332-0012, Japan Received: August 2, 2004; Revised: August 24, 2004; Accepted: August 24, 2004; DOI: 10.1002/marc.200400347 Keywords: conformation; fluoride ion; fluoropolymers; luminescence; polysilanes; sensors Introduction Considerable research has focused on the recognition and sensing of anions, owing to their vital roles in biological, environmental, and industrial processes. [1,2] In comparison to the relatively simple design principle for cation receptors based on electrostatic interactions and size, the design of highly sensitive and selective anionic receptors is challeng- ing because of their smaller charge to size ratio, a wide range of geometries, high solvation energies, and sensitivity to pH. [1] In particular, the sensing of fluoride ions has received much attention only in recent years because of its potential relevance to health, [3,4] to the analysis of drinking water, [5] and to the detection of chemical warfare agents. [6,7] The design of receptors for fluoride ions is mainly based on the supramolecular materials utilizing hydrogen bond- ing [1,8–12] and Lewis acid –base interactions. [13–15] Recently, the conjugated polymers have received a great deal of attention as fluorescent chemosensors, because these can provide signal amplification for the highly sensitive fluorimetric method. [16] Mostly positively charged [16–20] or neutral species [16,21–23] have been detected by fluorescent chemosensors based on the conjugated polymers, as com- pared with only a few examples for anion detection. [24,25] Recently, we reported the facile synthesis of a s-conjugated fluoroalkylated polysilane, poly(3,3,3-tri- fluoropropylmethylsilane) (1), by the sodium-mediated coupling reaction of 3,3,3-trifluoropropylmethyldichloro- silane in octane. [26] The cooperative weak Si  F–C interactions between the trifluoropropyl side-chain and the silicon main-chain led to the stabilization of a rodlike conformation of 1. [26,27] The latent affinity of Si atoms Summary: This paper reports a new and simple approach for the amplified detection of fluoride ions by a polymer-based chemosensor made of stiff fluoroalkylated polysilane, poly- (3,3,3-trifluoropropylmethylsilane). This chemosensor exhi- bited extreme sensitivity and selectivity towards fluoride ions by a decrease in the photoluminescence (PL) intensity with parts per billion concentrations of fluoride ions in solution in tetrahydrofuran (THF). The quenching constant for fluoride ions (K ¼ 1.35  10 7 M 1 ) was found to be exceptionally high. Schematic representation of the polymer amplification mechanism after addition of fluoride ion in tetrahydrofuran. Macromol. Rapid Commun. 2004, 25, 1771–1775 DOI: 10.1002/marc.200400347 ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Communication 1771 a : Supporting information for this article is available at the bottom of the article’s abstract page, which can be accessed from the journal’s homepage at http://www.mrc-journal.de, or from the author.