Helical self-assembly and amplification in chirality in fluorinated, preorganized discotic systems (mixing on the molecular level with apolar discs)
ArticleHoutem, van, M.H.C.J., Benaskar, F., Fitie, C.F.C., Martin-Rapun, R., Vekemans, J.A.J.M. & Meijer, E.W. (2012). Helical self-assembly and amplification in chirality in fluorinated, preorganized discotic systems (mixing on the molecular level with apolar discs). Organic & Biomolecular Chemistry, 10(30), 5898-5908. In Scopus Cited 14 times.
The synthesis and self-assembly properties of a fluorinated C3-symmetrical 3,3'-bis(acylamino)-2,2'-bipyridine discotic (1) in the mesophase and in solution are described. First, 3,4,5-tris-(1H,1H,2H,2H,3H,3H-perfluoroundecyl-1-oxy)benzoyl chloride was coupled to mono-t-BOC protected 2,2'-bipyridine-3,3'-diamine to afford after deprotection the corresponding fluorinated aromatic amine on a multigram scale. Then, three-fold reaction of this amine with trimesyl chloride yielded the target C3-symmetrical fluorinated disc. The latter displayed columnar liquid crystallinity over a temperature range of more than 350 K in which helical rectangular and hexagonal columnar mesophases were detected by X-ray diffraction measurements. 1H-NMR spectroscopy showed a preorganized structure due to strong intramolecular hydrogen bonding between the amide N–H's and bipyridine nitrogen atoms, even in the presence of a large excess of hexafluoroisopropanol. This preorganized structure allows the formation of helical self-assemblies in fluorinated solvents, as was established using UV-Vis spectroscopy. The fluorinated disc and two chiral hydrocarbon analogues (a C3-symmetrical and a desymmetrized disc) were mixed in a 1:10 v:v mixture of methoxynonafluorobutane (MNFB) and 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113). Importantly, the C3-symmetrical hydrocarbon disc dissolves only in the presence of fluorinated disc in the latter solvent mixture, proving a mutual interaction. CD spectroscopy performed on these mixtures points to a preference for alternating self-assemblies of fluorinated and chiral hydrocarbon discotics.