title: Synthesis and radical coupling of pyridine-bridged pi-extended tetrathiafulvalene (TTF)-type donors and push-pull analogues.
abstract: A new family of pi-extended TTF analogues (3a-c) and D-pi-A chromophores (5a-c), in which the electroactive units (1,3-dithiole rings and 2,2-dicyanovinyl groups) are connected through a pyridine bridge with a meta substitution pattern, is reported. The redox behavior of these compounds has been investigated by cyclic voltammetry and theoretical calculations performed at the B3P86/6-31G** level. Unlike many pi-extended TTF derivatives, the 1,3-dithiole rings in compounds 3a-c do not behave independently and two oxidation processes are observed with an anodic separation ranging from 50 to 150 mV. Calculations show that electrons are equally extracted from both dithiole rings. A biradical structure is predicted for the dication state due to the near-degeneracy of the HOMO and HOMO - 1 orbitals. The presence of both donor (D) and acceptor (A) fragments in conjugates results in irreversible oxidation and reduction processes associated with the 1,3-dithiole ring and with the 2,2-dicyanovinyl moiety, respectively. An electrochemical-chemical-electrochemical (ECE) process takes place for all the compounds reported. The chemical process implies the dimerization of the radical cation for compounds 5 and the oligomerization of the biradical dication for compounds 3. The ECE process therefore generates new neutral dimeric (5) or oligomeric (3) species that incorporate the TTF vinylogue core.
authors.affiliation: Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040, Madrid, Spain.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Priego
authors.forename: Luis
authors.initials: L
authors.lastname: Sánchez
authors.forename: M
authors.initials: M
authors.lastname: Angeles Herranz
authors.forename: Nazario
authors.initials: N
authors.lastname: Martín
authors.forename: Rafael
authors.initials: R
authors.lastname: Viruela
authors.forename: Enrique
authors.initials: E
authors.lastname: Ortí