A (π-Extended Tetrathiafulvalene)−Fluorene Conjugate. Unusual Electrochemistry and Charge Transfer Properties:  The First Observation of a Covalent D²⁺−σ−A^•- Redox State¹

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 quasireversibility of the TTFAQ(2+) state and a low E(ox) - E(red) gap ( approximately 0.25 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-ylidene]-5-methyl-[1,3]dithiol-4-ylmethyl ester (10) has enabled the electrochemical generation of the hitherto unknown transient D(2+)-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(4,5-dimethyl-[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.

Combining High Electron Affinity and Intramolecular Charge Transfer in 1,3‐Dithiole–Nitrofluorene Push–Pull Diads

“…[35] In the most extreme case, the radical cation of a p-extended dithiole derivative is completely destabilised, which gives rise to a truly two-electron (inverted potentials) oxidation process. [35,36] In dithiole-fluorene diads, a complete coalescence of the first and second reduction waves has never been observed, although the thermodynamic stability of species AC À has a slight tendency to decrease with a reduction in the electronwithdrawing character of substituents in the fluorene moiety (cf. K disp = 0.9 10 À4 for 7 a and 29 10 À4 for 7 f, Table 1).…”

Competition of Aromatic Bromination and Nitration in Concentrated Sulfuric Acid

“…4,5-Dibromo-2,7-dinitro-fluorenone 15, isolated in the pure state, turns to 5-bromo-2,4,7-trinitrofluorenone 14 at repeated processing. It allows to synthesize 5-bromo-2,4,7-trinitrofluorenone 14 directly from unsubstituted fluorenone 16 by heating till disappearance of 4,5-dibromo-2,7-dinitrofluorenone 15 instead of nitration and after that bromination as in the work [18]. Transformation proceeds evidently through a stage of bromine elimination (protodebromination) and subsequent nitration.…”

How the Anchoring Site on Two Extended Tetrathiafulvalenes Impacts the Electronic Communication through a Bis(acetylide)ruthenium Linker

“…8 This molecular motion concerted with the electron transfer leads to pseudo reversible cyclic voltammogram where the compound oxidizes into the dication with potential inversion. 9,10 TTFAQ dimers have also been synthetized either as macrocyclic receptors for C 60 recognition 11,12 or as positive electrode materials for rechargeable batteries. 13 In order to form TTFAQ dimers, different strategies have been used: either the two redox active cores are directly connected to each other, or a spacer group is used.…”