Metallomesogens derived from benzoxazoles–salicylaldimine conjugates
摘要:
The synthesis, characterization, and mesomorphic properties of a new series of Schiff bases 2a-h and metal complexes 1a-h-M are prepared and their mesomorphic properties studied. Two single crystallographic structures of 2d (n=12, m=1) and 1g-Pd (n=m=12) were determined by X-ray analysis. Both compounds crystallize in a triclinic space group P-1. A dimeric structure formed by intermolecular H-bonds in 2d was observed, giving nematic phase due to a better aspect ratio. The central geometry at Pd2+ ion is nearly perfect square plane. All Schiff bases 2a-h formed N or/and SmC phases. The formation of mesophases of complexes 1a-h-M was strongly dependent on metal ions incorporated. All Cu2+, Ni2+ and Pd2+ complexes exhibited N or/and SmC phase, respectively. However. Zn2+ and Co2+ complexes were not mesogenic. The lack of mesomorphism was probably attributed to a preferred tetrahedral geometry at Zn2+ and Co2+ over a square-planar geometry at Cu2+ and Pd2+. (C) 2011 Elsevier Ltd. All rights reserved.
New Mesogenic Compounds Containing a Terminal-Substituted Benzoxazole Unit
摘要:
A series of novel mesogenic 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives bearing different substituents (H, NO2, CH3, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-C, respectively) at the 5-position were prepared and characterized. nPB-N, nPB-M, and nPB-C exhibited enantiotropic smectic mesophases with the mesophase ranges 3 degrees C-32 degrees C and 3 degrees C-82 degrees C on heating and cooling processes, whereas nPB-H showed no mesophases. The substituents with the stronger electron withdrawing effect let to the wider mesomorphic temperature domain. The nPB-M, nPB-C, and nPB-H displayed intense emission in CH2Cl2 solutions with lambda(max) peaks of the photoluminescence spectra at 350-355nm when excited at their absorption maxima.