ON THE SOLID POLYMORPHS OF THE DISCOTIC MESOGEN HEXA-OCTANOYLOXYTRIPHENYLENE

In an earlier study by van Hecke et al., it was shown that the discoti c mesogen hexa-octanoyloxytriphenylene (HAT8) crystallizes in four dif ferent solid forms, depending on the thermal history of the sample. Th e present study is an attempt to characterize three of these solids in more detail using X-ray, carbon-13 and deuterium NMR techniques. It i s shown that van Hecke's modification IV is a metastable amorphic soli d, while modifications III and II are highly ordered crystalline solid s. Both are apparently monoclinic, but with different unit cell dimens ions. In all solid phases, the triphenylene core is static on the NMR time-scale, but the side chains are disordered to different degrees in the different modifications. Further NMR studies on the discotic meso phase of HAT8 are also reported.