Tailoring Valence Tautomerism by Using Redox Potentials: Studies on Ferrocene‐Based Triarylmethylium Dyes with Electron‐Poor Fluorenylium and Thioxanthylium Acceptors
Larissa A. Casper, Michael Linseis, Serhiy Demeshko, Mykhailo Azarkh, Malte Drescher, Rainer F. Winter
Abstract
Abstract Three new electrochromic ferrocenyl triarylmethylium dyes with fluorenylium ( 1 a + , 1 b + ) or thioxanthylium ( 1 c + ) 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 (VT). UV/Vis/NIR and quantitative EPR spectroscopy identified paramagnetic diradical isomers 1 a ..+ – 1 c ..+ alongside diamagnetic forms 1 a + – 1 c + , which renders these complexes magnetochemical switches. The diradical forms 1 a ..+ – 1 c ..+ as well as the one‐electron‐reduced triarylmethyl forms of the complexes were found to dimerize in solution. For radical 1 a . , dimerization occurs on the timescale of cyclic voltammetry; this allowed us to determine the kinetics and equilibrium constant for this process by digital simulation. Mößbauer spectroscopy indicated that 1 a + and 1 b + retain VT even in the solid state. UV/Vis/NIR spectro‐electrochemistry revealed the poly‐electrochromic behaviour of these complexes by establishing the distinctly different electronic absorption profiles of the corresponding oxidized and reduced forms.