Polymerization of cysteine functionalized thiophenes Rita Cagnoli a , Massimiliano Lanzi b , Adele Mucci a , Francesca Parenti a , Luisa Schenetti a, * a Dipartimento di Chimica, Centro SCS, Universita ` di Modena e Reggio Emilia, via G. Campi 183, 41100 Modena, Italy b Dipartimento di Chimica Industriale e dei Materiali, Universita ` di Bologna, viale Risorgimento 4, 40136 Bologna, Italy Received 25 January 2005; received in revised form 11 March 2005; accepted 13 March 2005 Available online 7 April 2005 Abstract Different synthetic pathways leading to polythiophenes (PTs) containing units derived from methyl N-(tert-butoxycarbonyl)-S-3-thienyl- L-cysteinate (1) and methyl N-(tert-butoxycarbonyl)-S-(2-thien-3-ylethyl)-L-cysteinate (2) were investigated. The oxidative coupling with FeCl 3 applied to N-deprotected monomer 1 generates a chemically fleeting PT, whereas when applied to N-deprotected monomer 2 generates a mixture of oligomers. Two co-polymers bearing cysteine moieties, poly{[methyl N-(tert-butoxycarbonyl)-S-3-thienyl-L-cysteinate]-co- thiophene} (co-PT1) and poly{[methyl N-(tert-butoxycarbonyl)-S-(2-thien-3-ylethyl)-L-cysteinate]-co-thiophene} (co-PT2), were even- tually synthesized through Stille coupling of 2,5-bis(trimethylstannyl)thiophene and 2,5-dibromo derivative of compound 1 and through the post-functionalization with protected cysteine of a tosylate co-polymer, poly{[2-(3-thienyl)ethyl 4-methylbenzenesulfonate]-co-thiophene} (co-PTTs). UV–vis, CD, NMR and GPC analyses evidenced that these polymers are able to form chiral self-assembling structures, due to the formation of a hydrogen bond network and to p-stacks, not only in the solid state but also in solution. q 2005 Elsevier Ltd. All rights reserved. Keywords: Polythiophenes; Cysteine; Stille coupling 1. Introduction One of the most interesting fields of research is represented, at the present time, by the design, synthesis and characterization of organic semiconducting materials able to detect and transduce physical or chemical infor- mation into electrical or optical signals [1]. Among organic semiconductors, substituted polythiophenes (PTs) play a significant role since, they possess good stability and permit the insertion of functionalities which allow processability in different environments [2]. These materials combine the electroactive properties of PT with those due to the side chain groups, and PT based devices, as modified electrodes or sensors, have been developed for applications both in gas phase and in solution in order to identify organic compounds, ions and biomolecules [2,3]. The insertion of an amino acid on a synthetic polymer backbone is very intriguing since, it can lead to the obtainment of macromolecules useful for ion and molecular recognition and possessing biomimetic characteristics [4]. Nevertheless, only the Ingana ¨s group has reported on the synthesis and properties of a PT functionalized with a serine moiety, linked through an ethylenic spacer to a thiophene ring [5]. We recently reported the preliminary results on a co- polymer of methyl N-(tert-butoxycarbonyl)-S-thien-3-yl- cysteinate and thiophene [6]. Cysteine directly bonded to thiophene ring (through the sulfur atom) was chosen on the basis of our previous studies on oligo- and poly(alkylsulfa- nyl)thiophenes, which have shown that the sulfur atom positively influences the characteristics of these PTs in comparison to polyalkylthiophenes, especially when film- ability and p- and n-doping are concerned [7]. Polymers bearing a cysteinic side chain seem to us very attractive as they possess three potential sites (the thioether, the carboxy and the amino group) for molecular interaction, metal-ion detection and self-assembling through hydrogen bond formation. Furthermore, the chirality of the amino acid should make these polymers suitable for chiral recognition and induce chain helicity in aggregated phases [4]. In the present work we report on the generation of PTs bearing a cysteinic side group directly bonded, through the sulfur atom, to the thiophene ring or two-bond remote from it. Methyl N-(tert-butoxycarbonyl)-S-3-thienyl-L-cysteinate Polymer 46 (2005) 3588–3596 www.elsevier.com/locate/polymer 0032-3861/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2005.03.031 * Corresponding author. Tel.: C39 59 2055076; fax: C39 59 373543. E-mail address: schene@unimo.it (L. Schenetti).