Orientational Behaviour of Phosphonic Acid Dialkyl Esters in Nematic and Smectic Phases of Pentoxy-benzylidene-hexylaniline Studied by1H,2H, and31P NMR

Abstract

Abstract The orientational behaviour of a variety of phosphonic acid diesters dissolved in different liquid crystalline phases of pentoxy-benzylidene-hexylaniline was studied. For the complete determination of the orientational ordering of the phosphonate segment, partially deuteratcd esters were synthesized and a combination of 31P, 2H and 1H NMR was used. For solutions of hexane phosphonic diethyl ester dissolved in the nematic and SA phases, the order parameter, S33 increases from 0.22 to 0.42 with a biaxiality of 0.1. The CH2 P(O)O2, segment is in the trans-conformation and the Sv axis makes an angle of 22° with the P=0 bond. In the SB phases the value of S31 of the phosphonate segment decreases dramatically to a value of 0.1 in contrast to that of the molecules of the matrix. The reason is that the solute molecules are excluded from the more ordered aromatic region and are forced into the less-ordered hydrocarbon chain region of the matrix. In the SG phase, a phase separation occurs. In diethyl ester...