Dr. Fenton Heirtzler

Ph.D. Organic Chemist in Central New Jersey

Liquid Crystalline Metallocyclophanes

Liquid Crystalline Metallocyclophanes

 

    Metallocyclophanes are flat, dimeric structures formed by the self-assembly of oligopyridine/pyrazine or oligopyridine/quinoxaline ligands with kinetically labile metal ions, such as copper(I), silver(I) or cobalt(II). Both copper(I) and silver(I) have tetrahedral binding domains, and this is well accommodated by the bidentate binding domains of compound 1; see Equation 1. One quinoxaline N atom remains uncomplexed in the metallocyclophane.

Metallocyclophane self assembly

Equation 1

 

    Molecules having both lipophillic and polar domains can form liquid crystals. In 2008, we showed that oligopyridine/quinoxaline ligands containing long-chain polyethers will, when combined with Ag(I) salts, form liquid crystalline, disilver(I)  metallocyclophanes. The corresponding dicopper(I) metallocyclophanes are low-melting, non-liquid crystalline complexes. The structure of a typical dicopper(I) metallocyclophane from a long-chain ligand 2n is shown below.

long chain dicopper(I) metallocyclophane

 

    Liquid crystalline Ag(I) complexes are of interest for electronic display technologies. The complexes of Cu(I) with oligopyridine-type ligands, on the other hand, are luminescent, and have been identified as candidate materials in electroluminescent displays and organic photovoltaic semiconductors.

 

    The challenge, which we have identified, is therefore to synthesize an improved generation of ligands. These will form liquid crystalline dicopper(I) metallocyclophanes. For example, ligands resembling molecule 3n will feature phenyl groups as spacers between the polar metal coordination sites and the lipophillic alkyl chains. This feature is well-known to favor liquid crystallinity. The synthesis of 3n is well underway.

phenyl-spaced ligands