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Synthesis of 3,4-Disubstituted Poly(thiophene)s via Substitution of Poly(3-alkylthiophene) Yuning Li, George Vamvounis and Steven Holdcroft* Department of Chemistry, Simon Fraser University, Burnaby, BC, Canada ABSTRACT The electrophilic substitution of regioregular poly(3-hexylthiophene) (P3HT) at the 4position was investigated to produce structurally well defined 3,4-disubstituted poly(thiophene)s. When P3HT was treated with N-bromosuccinimide (NBS) in chloroform at 25 to 50 °C, the 4hydrogen atom in P3HT is completely substituted by bromine, as indicated by the 1H NMR, 13C NMR and elemental analysis. Similarly, the chlorinated product was obtained using Nchlorosuccinimide (NCS) at room temperature. However, only 85% of the 4-hydrogen atoms were replaced by chlorine and ~15% of the α-hydrogen atoms on the hexyl side chain were chlorinated. P3HT readily reacts with fuming nitric acid in chloroform at 0 °C to generate a nitrated product with almost 100% substitution at the 4-position. Our preliminary study on the futher functionalizaton of these polymers was conducted on the brominated product. Our results showed that the bromine atom in this polymer could be further substituted with other groups. INTRODUCTION Poly(thiophene)s are a representative class of conjugated polymers because of their remarkable electrical, electronic, and optical properties [1]. Tremendous interest has been paid to these polymers since they can be solubilized by substitution of the thiophene ring with butyl or longer alkyl side chains [2]. The solubility of substituted poly(thiophene)s not only confers the processability, but also allows unambiguous elucidation of their structure and intrinsic properties. Furthermore, substitution (or functionalization when the substituents are viewed as functional groups) of the thiophene ring can be used to control and fine-tune the chemical, electronic, and optical properties [1]. In this way, highly conductive, water soluble, selfassembled, stimuli-sensitive, and luminescent poly(thiophene)s have been developed. To date, substitution or functionalization of poly(thiophene)s is approached solely from the polymerization of pre-functionalized monomers. However, reaction conditions of the most commonly used preparative polymerization methods (e.g., electropolymerization, oxidative polymerization using FeCl3 [2], the Rieke-Zinc method [3], and the McCullough-Grignard coupling method [4], etc.) are often too harsh for the functional group to survive. Thus only poly(thiophene)s with robust functional groups (e.g., alkyl, alkoxy) are accessible by this approach [5]. An alternate route to functionalized poly(thiophene)s is the post-functionalization of precursor polymers. This methodology has been successfully exploited for many conventional non-conjugated polymers [6]. However, only a few examples of post-functionalization of conjugated polymers can be found in the literature [7]. Regioregular poly(3-alkylthiophene)s offer intrinsic electrical and electronic properties over regiorandom analogs [8]. These polyme