Mesomorphic 4'-functionalized 6'-phenyl-2,2'-bipyridines: tridentate ligands for organopalladium mesogens

A novel series of 6′-phenyl-2,2′-bipyridines (HL-n) substituted in the 4′ position with promesogenic functional groups has been prepared. The materials are strongly luminescent and display nematic mesomorphism. The HL-n behave as C,N,N-tridentate, cyclometallating ligands leading to [Pd(L-n)Cl] derivatives. Metal co-ordination promotes a considerable stabilization of the crystal phase, forcing mesophases to become metastable. All [Pd(L-n)Cl] species indeed exhibit a monotropic mesophase either nematic or smectic A in character depending on the chain length of the substituents on the central pyridine unit.