title: Highly conjugated p-quinonoid pi-extended tetrathiafulvalene derivatives: a class of highly distorted electron donors.
abstract: A new class of pi-extended TTF-type electron donors (11 a-c) has been synthesized by Wittig-Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10 a-c). In cyclic voltammetry experiments, donors 11 a-c reveal a single, electrochemically irreversible oxidation-yielding the corresponding dicationic products-at relatively low oxidation potentials (approximately 0.7-0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6-31 G*), predict a highly-folded C(2h) structure for 11 a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO-->LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11 a*+ retains the folded C(2h) structure predicted for the neutral molecule as the most stable conformation, the dication 11 a(2+) has a fully aromatic D(2) structure, formed by an orthogonal 9,9'-bianthryl central unit to which two singly-charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical-induced one-electron oxidation of 11 a-c was shown to lead to the radical cation species (11 a-c*+), which were found to disproportionate with generation of the respective dication species (11 a-c(2+)) and the neutral molecules (11 a-c).
authors.affiliation: Departamento Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain.
authors.forename: Marta C
authors.initials: MC
authors.lastname: Díaz
authors.forename: Beatriz M
authors.initials: BM
authors.lastname: Illescas
authors.forename: Nazario
authors.initials: N
authors.lastname: Martín
authors.forename: Rafael
authors.initials: R
authors.lastname: Viruela
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Viruela
authors.forename: Enrique
authors.initials: E
authors.lastname: Ortí
authors.forename: Ortwin
authors.initials: O
authors.lastname: Brede
authors.forename: Israel
authors.initials: I
authors.lastname: Zilbermann
authors.forename: Dirk M
authors.initials: DM
authors.lastname: Guldi