Relevant chiroptical and thermal properties in optically active methacrylic copolymers containing carbazole and azoaromatic chromophores in the side-chain Luigi Angiolini * , Tiziana Benelli, Loris Giorgini, Francesco Mauriello, Elisabetta Salatelli Dip. di Chimica Industriale e dei Materiali and INSTM UdR-Bologna, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy article info Article history: Received 4 September 2009 Received in revised form 9 September 2009 Accepted 20 September 2009 Available online 24 September 2009 Keywords: Photochromic polymers Amplification of chirality Multifunctional materials Carbazole polymers Azopolymers abstract Novel optically active methacrylic copolymers, bearing carbazole and azoaromatic moieties linked to the main chain with a rigid (S)-hydroxysuccinimide residue of one prevailing absolute configuration, have been prepared and characterized with the aim to establish the effects of the chiral group and of the dipo- lar interactions between the two side-chain chromophores on their properties. In particular, the observed chiroptical properties suggest the presence of ordered chiral conformations at least for chain segments of the macromolecules. Spectroscopic, thermal and chiroptical characteriza- tions of these copolymers demonstrate the occurrence of significant electronic interactions between car- bazole chromophores and azobenzene moieties. These interactions are related to the unusual partially alternating structure of the investigated copolymers and the relevant chiroptical and thermal properties. In fact, the polymeric derivates show high glass transition temperatures and good thermal stability, thus opening the way to a variety of potential applications based on photoconductive and optoelectronic properties. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Carbazole-containing polymers [1–5] have attracted much attention because of their unique properties, for example the hole-transporting and electroluminescence properties. Recently [6] we have reported novel chiral homopolymeric methacrylate poly[(S)-(+)-2-methacryloyloxy-N-[3-(9-ethylcar- bazolyl)]succinimide] {poly[(S)-(+)-MECSI]} bearing the optical active residues of (S)-2-hydroxy-succinimide interposed between the methacrylic main chain and the carbazolic chromophore (Scheme 1). The properties of this particular class of optically active carbazole polymers may allow a variety of potentially commercial applications as NLO, photoconductive and photorefractive materials. On the other hand, in the last decades, an intense attention has been arisen to investigations dealing with side-chain polymers containing azoaromatic chromophores for their optical properties [7–11] and for their use in advanced micro- and nanotechnologies such as optical data storage [12,13], NLO materials [14,15], holo- graphic memories [16–18], chiroptical switches [19,20], and sur- face relief gratings [21,22]. In this context the induction of helical chirality in polymers has attracted widespread interest for its possible applications in optical devices or data storage also because of its relevance to chiral amplification as it may have occurred at the early stages of life [23]. To this regard, in recent studies we have reported on optically active photochromic methacrylic polymers bearing two distinct functional groups (i.e. the azoaromatic and a chiral group of one single configuration) directly linked to the side-chain [24–27]. In these materials, the simultaneous presence of these functionalities allows the polymers to display both the properties typical of dis- symmetric systems (optical activity, exciton splitting of dichroic absorptions), as well as the features typical of photochromic mate- rials (photorefractivity, photoresponsiveness, NLO properties). In this context, it appeared interesting to investigate the proper- ties of novel multifunctional copolymeric materials containing both the photoresponsive azobenzene and the photoconducting carba- zole chromophore directly linked to the polymeric side-chain through the chiral moiety. Additionally, the contemporary presence of electron-rich carbazole and electron-poor azobenzene chro- mophores could lead to the establishment of charge-transfer inter- actions that are at the basis of photoconducting carbazole materials. In the literature interesting achiral copolymers of N-vinylcar- bazole (NVK) with 4-methacryloyloxyazobenzene (MAB) and 4- methacryloyloxy-4 0 -cyanoazobenzene (MCA), characterized by prevailing co-units alternation and the occurrence of elevated charge-transfer electronic interactions between the chromophores are reported [28]. Multifunctional derivatives, bearing three distinct functional groups (azoaromatic, carbazolic, and chiral), could be of potential 1381-5148/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2009.09.005 * Corresponding author. Tel./fax: +39 051 2093687. E-mail address: luigi.angiolini@unibo.it (L. Angiolini). Reactive & Functional Polymers 69 (2009) 898–904 Contents lists available at ScienceDirect Reactive & Functional Polymers journal homepage: www.elsevier.com/locate/react