Mesomorphic behavior of hybrid triphenylene-siloxane oligomers

FLORENCIA CECCHI; ANDRÉS ZELCER; BERTRAND DONNIO; DANIEL GUILLON; FABIO D. CUKIERNIK

Colmar, Francia

Conferencia; X EUROPEAN CONFERENCE ON LIQUID CRYSTALS; 2009

            Substituted triphenylenes have been widely studied as discotic mesogens. They form primerly nematic and columnar mesophases[1] with potential applications as 1-D charge migration due to the p-p interactions between the aromatic cores[2], with the advantage that they can be easily processed. However, the lack of long-range order along the column, limits the charge-carrier mobility (10-3-10-1 cm2 V-1s-1)[3]. To improve this property it is necessary to obtain macroscopically aligned and stable monodomains of these materials.             A multiblock molecular architecture design of the discotic mesogen could be used as strategy to minimize the intracolumnar stacking fluctuations. The micosegregation between the different chemical parts of the mesogen favours core-core interactions[4]. Other possibility is to introduce covalent bonds between mesogens (as in oligomers and polymers) to reduce the freedom degrees of the aromatic core.             In this context, we synthetized the triblock triphenylene-carbosiloxane monomer, dimer, trimer and linear main-chain polymer (fig. 1). The compounds were characterized by 1H-NMR, MALDI-TOF and elemental analysis. The liquid crystalline properties were studied by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and variable temperature X-ray diffraction (XRD). The thermal data show that there is a gradual increase in the clearing temperature as the molecular mass increases (76ºC for the monomer against 106ºC for the polymer), while there is only a very small increase in the melting temperature (from 43ºC to 50ºC ca).             n   Figure 1:  Schematic representation of the monomer, dimer, trimer and polymer synthetized. [1] S. Kumar S, Liq. Cryst. 2004, 31,1037-1059 [2] N. Boden , B. Movaghar. Handbook of Liquid Crystals: Wiley-VCH: NY, 1998; Vol 2B, Chapter IX, pp 781-798. [3]R. J. Bushby.,O. R. Lozman,, Curr. Opin Solid state Mat. Sci. 2002,6,569 [4] A. Zelcer, B. Donnio ,C. Bourgogne , F. D. Cukiernik, D. Guillon, Chem. Mat. 2007, 19, 1992-2006