Chiral cyclic trinuclear gold(I) complexes with a helical columnar phase

Abstract

Cyclic trinuclear gold(I) complexes with chiral 3,5-diarylpyrazolate ligands have been synthesized and characterized with the aim of obtaining helical columnar liquid-crystal phases as a way to control the stacking geometry and orientation of the trigold metallacycle in the bulk phase. The compounds bear n-decyloxy- and/or (S)-3,7-dimethyloctyloxy terminal groups in a number varying from twelve to eighteen. The compounds behave like isotropic glasses, crystalline solids, or columnar liquid crystals (of hexagonal or rectangular symmetry), with isotropization temperatures close to room temperature. In the case of the compound bearing nine n-decyloxy- and nine (S)-3,7-dimethyloctyloxy terminal groups, a helical columnar phase is obtained that exhibits a well-formed hexagonal bidimensional lattice made of columns that consist of molecules stacked at regular distances and mutually rotated by 40° in a helical mode. Thin films display emission bands at room temperature in the blue region of the visible spectra, regardless of the phase or the molecular structure.