Based on a model consideration summarized in Fig. 1 systematic syntheses of liquid crystalline polymers with nematic, smectic and cholesteric phases have been realized'). The principal concept was to link conventional mesogenic groups to a polymer main chain via flexible spacer groups. A direct fixation of the mesogenic groups to the polymer main chain causes a coupling of the motions of the main chain and the mesogenic side chain. Thus-as stated by many publications in the field and summarized in recent reviews2)-the high mobility of chain segments in the liquid state of the polymer and its tendency towards a statistical chain conformation consequently prevents an anisotropic orientation of the mesogenic side chains above the glass transition temperature of the polymer. If the mesogenic groups are fixed via flexible spacer to the main chain the motions of the main chain and the side chains might be decoupled. In this case the mesogenic moieties are able to build up the orientational long range order although the motions of the main chain tend to prevent an anisotropic order. Following these model considerations, the liquid crystalline state of the polymers should be independent of the nature of the main chain and-as it is known for conventional low molecular weight liquid crystals-should be determined only by the nature of the mesogenic group. This so far could only be confirmed by using benzoic acid phenyl ester derivatives LINKAGE OF THE MESOGENIC SIDE CHAIN TO THE MAIN CHAIN P COUPLES MOTIONS

A giant anti-Stokes photoluminescence is observed at low excitation densities on specially designed semimagnetic II-VI asymmetric double quantum well structures by applying an external magnetic field. The signal is due to a two-step absorption process, mediated by a long-living spatially indirect exciton, created via rapid electron tunneling from the primarily excited direct exciton state.

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