title: The interplay of inverted redox potentials and aromaticity in the oxidized states of new pi-electron donors: 9-(1,3-dithiol-2-ylidene)fluorene and 9-(1,3-dithiol-2-ylidene)thioxanthene derivatives.
abstract: Derivatives of 9-(1,3-dithiol-2-ylidene)fluorene (9) and 9-(1,3-dithiol-2-ylidene)thioxanthene (10) have been synthesised using Horner-Wadsworth-Emmons reactions of (1,3-dithiol-2-yl)phosphonate reagents with fluorenone and thioxanthen-9-one. X-ray crystallography, solution electrochemistry, optical spectroscopy, spectroelectrochemistry and simultaneous electrochemistry and electron paramagnetic resonance (SEEPR), combined with theoretical calculations performed at the B3P86/6-31G** level, elucidate the interplay of the electronic and structural properties in these molecules. These compounds are strong two-electron donors, and the oxidation potentials depend on the electronic structure of the oxidised state. Two, single-electron oxidations (E(1)ox < E(1)ox) were observed for 9-(1,3-dithiol-2-ylidene)fluorene systems (9). In contrast, derivatives of 9-(1,3-dithiol-2-ylidene)thioxanthene (10) display the unusual phenomenon of inverted potentials (E(1)ox > E(1)ox) resulting in a single, two-electron oxidation process. The latter is due to the aromatic structure of the thioxanthenium cation (formed on the loss of a second electron), which stabilises the dication state (10(2+)) compared with the radical cation. This contrasts with the nonaromatic structure of the fluorenium cation of system 9. The two-electron oxidation wave in the thioxanthene derivatives is split into two separate one-electron waves in the corresponding sulfoxide and sulfone derivatives 27-29 owing to destabilisation of the dication state.
authors.affiliation: Department of Chemistry, University of Durham, Durham DH1 3LE, UK.
authors.forename: Samia
authors.initials: S
authors.lastname: Amriou
authors.forename: Changsheng
authors.initials: C
authors.lastname: Wang
authors.forename: Andrei S
authors.initials: AS
authors.lastname: Batsanov
authors.forename: Martin R
authors.initials: MR
authors.lastname: Bryce
authors.forename: Dmitrii F
authors.initials: DF
authors.lastname: Perepichka
authors.forename: Enrique
authors.initials: E
authors.lastname: Ortí
authors.forename: Rafael
authors.initials: R
authors.lastname: Viruela
authors.forename: José
authors.initials: J
authors.lastname: Vidal-Gancedo
authors.forename: Concepció
authors.initials: C
authors.lastname: Rovira