Five Shades of Green: Substituent Influence on the (Spectro-) Electrochemical Properties of Diferrocenylphenyl Methylium Dyes

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.