STABILIZATION AND INDUCTION OF DISCOTIC MESOPHASES BY TRIFLUOROACETIC-ACID

It is shown that trifluoroacetic acid (TFA) can form 1:1 molar complex es with alkyloxy discotic compounds, thereby enhancing their mesomorph ic properties. In particular, when hexa-alkyloxytriphenylenes (THEn) ( n being the number of carbons per side chain) are crystallized from, o r mixed with, TFA, complexes are formed which exhibit the D-ho(Col(ho) ) mesophase, as do the neat THEn's, but with a broader range of therma l stability and a higher degree of order. The mesophases of these comp lexes are completely miscible with those of the neat compounds. Likewi se, 1:1 mixtures of hexa-alkyloxytribenzocyclononene (TBCEn) and TFA y ield complexes showing enhanced mesomorphic properties for the mesogen ic homologues of this series and induced mesomorphism for the lower ho mologues, which in the neat form are not mesogenic. The mesomorphic pr operties of these TFA complexes with THEn (n=3-6) and with TBCEn (n=4- 6) are investigated by means of optical microscopy, differential scann ing calorimetry, X-ray diffraction and NMR spectroscopy. It is suggest ed that the enhancement of the mesomorphic properties is due to format ion of oxonium ion complexes.