Tailoring Valence Tautomerism using Redox Potentials : Studies on Ferrocene‐Based Triarylmethylium Dyes With Electron‐Poor Fluorenylium and Thioxanthylium Acceptors

Abstract

Three new electrochromic ferrocenyl triarylmethylium dyes with fluorenylium ( 1a + , 1b + ) or thioxanthylium ( 1c + ) residues were selected in order to keep the intrinsic differences of redox potentials for ferrocene oxidation and triarylmethylium reduction small and to trigger valence tautomerism. UV/Vis/NIR and quantitative EPR spectroscopy identified paramagnetic diradical isomers 1a +•• ‐1c +•• alongside diamagnetic forms 1a + ‐1c + , which renders these complexes magnetochemical switches. The diradical forms 1a +•• ‐1c +•• as well as the one‐electron reduced triarylmethyl forms of the complexes were found to dimerize in fluid solution. For radical 1a • , dimerization occurs on the timescale of cyclic voltammetry, which allowed us to determine the kinetics and equilibrium constant for this process by digital simulation. Mößbauer spectroscopy indicated that 1a + and 1b + retain VT even in the solid state. UV/Vis/NIR spectroelectrochemistry revealed the polyelectrochromic behaviour of these complexes by establishing distinctly different electronic absorption profiles of the corresponding oxidized and reduced form s.