Viable synthesis of a self-assembling regioregular thiophenic copolymer for second-order non-linear optics Massimiliano Lanzi * , Paolo Costa-Bizzarri, Luisa Paganin, Gaia Cesari Dipartimento di Chimica Industriale e dei Materiali, Universita ` di Bologna, Viale del Risorgimento 4, I-40136 Bologna, Italy Received 27 November 2006; received in revised form 12 April 2007; accepted 15 April 2007 Available online 19 April 2007 Abstract Regioregular azobenzene-substituted polythiophenic copolymers were prepared by a regiospecific organometallic polycondensation procedure based on a Grignard metathesis reaction. Copolymers with a high content of chromophoric groups in the side chains and a high degree of configurational order of the backbones were obtained. A sample was also functionalized with hydroxyalkyl chains capable of setting up ordered supramolecular structures through hydrogen bonds. The final materials were fully characterized via NMR, IR, elemental analysis, GPC, DSC and X-ray diffraction. Moreover, measurements of NLO activity on polymer films showed the synthetic strategies adopted and monomers used to be correct. Values obtained by the in situ deprotection of the interacting functional groups after the alignment of the chromophorized side chains were very promising, proving the procedure to be suitable for industrial and commercial applications. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Functionalized polyalkylthiophenes; Regioregularity; Second-order NLO properties 1. Introduction Organic molecules as second-order non-linear optical (NLO) generators and conjugated polymers as electrooptic (EO) materials have been the subject of several studies over the past two decades chiefly for their indisputable advantages compared to inorganic materials [1e3]. In fact, the possibility of combining the electrical conductivity of metals, the NLO properties of some inorganic salts and the flexibility, structural versatility and low density of polymers in the same sample is an undoubted asset. In addition to the typical properties of ICPs (inherently conjugated polymers), polyalkylthiophenes (PATs) possess other specific characteristics such as good ther- mal and environmental stability even in the doped electrocon- ductive state [4], good processability, solubility and filmability [5] as well as the possibility to be synthesized through easy and cost-effective polymerization reactions [6]. In the present study post-polymerization functionalization (PPF), i.e. a simple and affordable way for inserting the desired functional group into polythiophenic side chains was performed according to the already optimized synthetic procedures [7]. More precisely, the NLO active chromophoric group was first introduced in a soluble polymeric precursor by the PPF pro- cedure and then strong inter-chain interactions were set up through hydrogen bonding during or immediately after the poling procedure of the side chains, using again a deprotection reaction on a polymeric moiety. Overall chain mobility thus comes to be limited so that high second-order NLO efficiency factor d 33 values are retained [8]. 2. Experimental part 2.1. Monomer synthesis 2.1.1. 2,5-Dibromo-3-(6-bromohexyl)thiophene (2,5BT6Br) 3-(6-Bromohexyl)thiophene (T6Br) (7.80 g, 31.6 mmol) synthesized according to Ref. [9] was solubilized in 32 ml of N,N-dimethylformamide (DMF) with 5.61 g (31.6 mmol) * Corresponding author. Tel.: þ39 (0)51 2093705; fax: þ39 (0)51 2093669. E-mail address: lanzi@ms.fci.unibo.it (M. Lanzi). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.04.022 Polymer 48 (2007) 3406e3412 www.elsevier.com/locate/polymer