Five shades of green: substituent influence on the (spectro-) electrochemical properties of diferrocenyl(phenyl)methylium dyes

Abstract

Five new, intensely green diferrocenylphenylmethylium complexes 1⁺–5⁺ with electron donating (EDG: 4-MeO, 4-Me, 4-Br) or withdrawing (EWG: 3,5-CF₃, 4-ⁿC₆F₁₃) substituents were synthesized and fully characterized. The substituent influence on their electrochemical and spectroscopic properties was investigated by cyclic voltammetry, UV/Vis/NIR and T-dependent EPR spectroscopy of the cationic as well as the oxidized (1²⁺–5²⁺) and reduced (1˙–5˙) species. The reduced forms equilibrate with their corresponding dimers (65–83%) with a clear substituent influence as expressed by their Hammett parameters in an ordering 4⁺ > 5⁺ > 3⁺ > 2⁺ > 1⁺. The structures of all five precursor carbinols 1-OH–5-OH and those of three of the diferrocenylphenylmethylium cations (1⁺, 4⁺–5⁺) were established by X-ray crystallography.