³¹P and ¹³C NMR Studies of a Liquid-Crystalline Cyclotriphosphazene Derivative: Orientational Characteristics and Contrasting Shielding Anisotropies for Inorganic and Organic Moieties

Abstract

31P and 13C NMR studies are reported for a smectic A liquid crystal of haxakis[4-dodecyl(4-biphenoxy)]cyclotriphosphazene. In an intense magnetic field, the long axes of the biphenylene fragments and the alkyl chains align along the magnetic field, and the cyclotriphosphazene (ctp) ring-normal points preferentially in the same direction. Orientational order parameters for the inorganic moiety (ctp fragment) and that for the organic moiety (biphenylene fragment) are determined independently from the 31P and 13C NMR spectroscopies, respectively. The two order parameters are revealed to take the same value, 0.45. The value is smaller than that for the conventional smectic A liquid crystals consisting of small organic molecules. Contrasting chemical shift anisotropies are revealed for the motionally averaged fragments: the least-shielding axis for the 31P nucleus lies on the ctp ring normal, while that for the aromatic 13C nucleus lies along the line connecting the two phenylene rings.