The role of chiral dopants in organic/inorganic hybrid materials containing chiral Schiff base Ni(II), Cu(II) and Zn(II) complexes

Chiral Schiff base complexes containing azo-groups, bis(N-R-1-cyclohexylethyl-4-phenyldiazenylsalicydenaminato) nickel(II), copper(II) and zinc(II) complexes, and without azo-groups, bis(N-R-1-cyclohexylethyl-3,5-dichlorosalicydenaminato) nickel(II), copper(II) and zinc(II) complexes, affording a distorted square planar trans-[MN2O2] coordination geometry were prepared. Organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) spincoat films of the complexes (both the azobenzene (AZ) containing type and the latter complexes of the AZ separated type) were assembled for a comparison of polarized UV light induced molecular arrangement caused by the Weigert effect. Investigation of the parameters for the optical anisotropy of the metal complexes as well as AZ suggested that the degree of increasing optical anisotropy of the containing type was higher than that of the separated type based on π–π∗ (of which a characteristic band appeared around 380 nm) and n–π∗ bands of polarized absorption electronic spectra. In the AZ containing type, the rigid nickel(II) or zinc(II) complexes easily increase the optical anisotropy compared to the flexible copper(II) complexes. In the AZ separated type, interestingly, enhancement of some CD bands suggests the role of chiral dopants of some complexes without azo-groups for AZ.

We have prepared several new chiral Schiff base nickel(II), copper(II) and zinc(II) complexes having bulky cyclohexyl groups and with or without azobenzene groups, and have also prepared organic/inorganic hybrid materials composed of these complexes (and azobenzene) as PMMA spincoat films. We have observed the intermolecular interactions of some complexes without azobenzene to act as chiral dopants for azobenzene after polarized UV light irradiation.Figure optionsDownload as PowerPoint slideHighlights
► Chiral Schiff base Ni(II), Cu(II) and Zn(II) complexes.
► Organic/inorganic hybrid materials showing supramolecular chirality.
► Steric effects of the chiral ligands of metal complexes as chiral dopants.