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Abstract
A new rational pathway to 2,7-difunctionalised-β-hexa-substituted triphenylenes is presented, requiring less protection/deprotection and purification steps than more conventional synthetic procedures in the framework of the ‘biphenyl route’. Main improvements are deprotection via alkaline hydrolysis of an ester in ethanol/water medium instead of using toxic and pyrophoric reagents like lithium diphenylphosphide, and the use of easily prepared brominated precursors instead of iodinated reagents for biphenyl synthesis. 4,4′-Diacetoxy-3,3′-bis(hexyloxy)biphenyl has been synthesised under this scheme, and characterised by proton nuclear magnetic resonance (1H NMR) spectrometry, elemental analysis and single-crystal crystallography. It crystallises in the P-1 space group, and exhibits a layered structure built-up through dipolar, C–H … π and C–H … O=C non-covalent interactions. This compound has been oxidatively coupled with 1,2-bis(hexyloxy)benzene to yield 2,7-dihydroxy-3,6,10,11-tetrakis(hexyloxy)triphenylene, a non-mesogen key precursor for the synthesis of the corresponding liquid-crystalline 2,7-difunctional triphenylenes. Indeed, a reactive 2,7-difunctional mesogen was prepared and used to produce new triphenylene-siloxane hybrid monomeric, trimeric and polymeric mesogens. All of them exhibited columnar hexagonal (Colh) mesophases.
Acknowledgements
We thank financial support from ANPCyT (PICT 25209, PME 01113 for X-ray diffractometer), UBACyT (X057), Secyt-Ecos (A01E05) and Conicet (fellowships for AZ and Cecchi). AZ, PA and FDC are members of the research staff of Conicet.
Notes
Present address for Andrés Zelcer: Gerencia Química, Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica, Av. Gral Paz 1499, B1650KNA, San Martín, Buenos Aires, Argentina