Dimesogenic compounds with an electron-attracting terminal group

Non-symmetric dimesogens composed of a classical aromatic mesogenic unit li nked to a cholesteryl moiety by a flexible spacer form several types of sme ctic periodicities: one is connected to the cholesteryl length and the othe r to the length of the associated dimesogens. In some peculiar cases, anoma lies of periodicity resulting from the competition between these incommensu rate lengths are observed through the occurrence of two-dimensional modulat ed phases or incommensurate low ordered smectic phases (S-ic)dagger. As par t of our continuing effort to understand the influence on the smectic arran gement of the molecular parameters of such non-symmetric dimesogens, new ho mologues with a cholesteryl unit linked by a penta-methylene spacer to an a romatic mesogenic moiety bearing different electron attracting terminal gro ups have been prepared. For these compounds, only the periodicity resulting from the associated dimesogens is observed. Nevertheless, an incommensurat e smectic phase can be induced by mixing one of these compounds with anothe r appropriate dimesogen. Molecular mechanics calculations suggest that the origin of the different smectic structures is strongly connected to the rep artition of electrostatic potential along the dimesogen.