SUPRAMOLECULA CHIRALITY IN NEW CHIRAL LIQUID CRYSTAL AZOPOLYMERS OBTAINED BY ATRP

Side-chain liquid crystal polymers (LCP) with tailored azobenzene moieties are widely studied due to the easy photomodulation of their properties (birefringence, non-linear optical properties and chiroptical properties) making them suitable for several applications as materials for holographic data recording, non-linear optics, artificial muscles or molecular switches.[1-5] The presence of a chiral group of one absolute configuration in the side chain can lead to induction of supramolecular chirality both in amorphous and liquid crystal state. Here, we present the synthesis by ATRP and the characterization of monodisperse chiral azopolymers of well-controlled structure (linear and three-arms star shaped) and different average molecular weights. These new azopolymers include L-lactic residues in the side chain, which can transmit their chirality to a supramolecular organization of the liquid crystal phase. The nature of the liquid crystal phases of the synthesized polymers has been characterized by powder X-ray diffraction (XRD) and polarized optical microscopy (POM). The chiroptical properties of thin films of the azopolymers were investigated before and after irradiation with right (R)- and left (L)- circularly polarized light (CP) by circular dichroism (CD). All the irradiated polymeric films displayed amplified CD signals, with the largest level of supramolecular photoinduced chirality exhibited by linear polymers. [1] T. Ikeda, O. Tsutsumi, Science 1995, 268, 1873. [2] S. Xie, A. Natansohn, P. Rochon, Chem. Mater. 1993, 5, 403. [3] T. Verbiest, M. Kauranen, A. Persoons, J. Mater. Chem. 1999, 9, 2005. [4] R.M. Tejedor, M. Millaruelo, L. Oriol, J.L. Serrano, R. Alcal\ue0, F.J. Rodr\uecguez, B. Villacampa, J. Mater. Chem., 2006, 16, 1674. [5] G. Iftime, F.L. Labarthet, A. Natansohn, P. Rochon, J. Am. Chem. Soc., 2000, 122, 12646