Metal Complexes:Novel Chiral Dopants with High Helical Twisting Power in Liquid Crystals

<正>1 Introduction A particularly efficient and elegant route to chiral mesophases is based on the addition of small amounts of an enantiomerically pure dopant to a nematic phase so that the latter is converted into a cholesteric phase(See Fig.1).Fig.1 A nematic phase is converted into a cholesteric phase Fig.2 Bis-chelated imine-alkoxy-titanium complexes2 ExperimetalBis-chelated imine-alkoxy-titanium complexes like 1 and 2 (Fig.2) have been synthesizedstarting from triphenyl-substituted aminoethanols, The octahedral complexes are obtained as pure diastereomers and enantiomers, and their configuration has been assigned by crystal structure analyses andCD spectroscopy. In various commercial nematic phases, they exhibit exceptionally high helical twisting power (HTP). Indeed, the highest HTP values reported sofar, including a "record" of 740 μm-1 has been reported with complex 2 (X=OEt)[1]. The application of the novel dopants seemsto meet commercial interest[2].The same type of chiral ligands also serve to synthesize boron complexes that exhibit significant HTP as well. Remarkably, the boron atom becomes a stereogenic center with a stable configuration.