C-Term Faraday Rotation in Low Symmetry tert-Butyl Substituted Polyferroceniums

Molecular thin films are currently being investigated as candidate materials to replace conventional atomistic inorganic crystal-based Faraday rotators. High symmetry paramagnetic species have been reported to exhibit large Verdet constants via magnetic field splitting of degenerate ground states. However, lower symmetry open-shell species have not been extensively studied. Herein, we report the Faraday rotation of two poly di-tert-butylferroceniums with diphenylsilane and vinylene linkers. Thin films of oxidized poly[(1,1'-di-tert-butylferrocenyl)diphenylsilane] [poly(Bufc-SiPh)] displayed a 30% increase in maximum Verdet constant relative to the previously reported decamethylferrocenium/PMMA composite, with Verdet constants of -4.52 × 10⁴ deg T^-1 m^-1 at 730 nm and 4.46 × 10⁴ deg T^-1 m^-1 at 580 nm. When a sp²-type linker was used, as with the oxidized poly(1,1'-di-tert-butyl-ferrocenylene)vinylene [poly(Bufc-C═C)], negligible Faraday rotation was observed. Hence, Faraday rotation can be maintained when molecular symmetry is broken, however orbital symmetry breaking in optical transitions of interest leads to a significant loss in magneto-optical activity.