On the solid polymorphs of the discotic mesogen hexa-octanoyloxytriphenylene

Abstract

In an earlier study by van Hecke et al., it was shown that the discotic mesogen hexa-octanoyloxytriphenylene (HAT8) crystallizes in four different solid forms, depending on the thermal history of the sample. The present study is an attempt to characterize three of these solids in more detail using X-ray, carbon-13 and deuterium NMR techniques. It is shown that van Hecke's modification IV is a metastable amorphic solid, while modifications III and II are highly ordered crystalline solids. Both are apparently monoclinic, but with different unit cell dimensions. 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 mesophase of HAT8 are also reported.