A (π-extended tetrathiafulvalene)-fluorene conjugate. Unusual electrochemistry and charge transfer properties: The first observation of a covalent D²⁺–σ–A˙⁻ redox state

Abstract

The synthesis of novel electrochemically amphoteric TTFAQ-sigma-A compounds (TTFAQ = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene, sigma = saturated spacer, A = polynitrofluorene acceptor) is reported. Their solution redox behavior is characterized by three single-electron reduction and one two-electron oxidation waves. Electrochemical quasi reversibility of the TTFAQ(2+) state and a low E-ox - E-red gap (approximate to0.25 V) for 3-(9-dicyanomethylene-4,5,7-trinitrofluorene-2-sulfonyl)-propionic acid 2-[10-(4,5-dimethyl-[1,3]dithiol-2-ylidene)-9,10-dihydroanthracen-9-ylid enel]-5-methyl-[1,3]dithiol-4-ylmethyI ester (10) has enabled the electrochemical generation of the hitherto unknown transient D2+-sigma-A(.-) state as observed in cyclic voltammetry and time-resolved spectroelectrochemistry. The ground state of compound 10 was shown to be ionic in the solid but is essentially neutral in solution (according to electron paramagnetic resonance). The X-ray structure of an intermolecular 1:2 complex between 2-[2,7-bis(2-hydroxyethoxy)-9,10-bis(4,5dimethyl-[1,3]dithiol-2-ylidene) -9,10-dihydroanthracene and 2,5,7-trinitro-4-bromo-9-dicyanomethylenefluorene, 14(.)(17)(2), reveals, for the first time, full electron transfer in a fluorene charge-transfer complex.