Highly Conjugated p-Quinonoid π-Extended Tetrathiafulvalene Derivatives: A Class of Highly Distorted Electron Donors

A new class of π‐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 (∼0.7–0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6‐31 G*), predict a highly‐folded C2h 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 C2h structure predicted for the neutral molecule as the most stable conformation, the dication 11 a2+ has a fully aromatic D2 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–c2+) and the neutral molecules (11 a–c). Una nueva familia de moléculas dadoras de electrones de tipo TTF π‐extendido, altamente conjugadas, (11 a–c) se han sintetizado mediante la reacción de olefinación de Wittig–Horner de la biantrona (9) con fosfonatos de 1,3‐ditiol (10 a–c). En los experimentos de voltamperometría cíclica, los dadores 11 a–c muestran una única onda de oxidación electroquímicamente irreversible—dando lugar a los productos dicatiónicos—a potenciales relativamente bajos (∼0.7–0.8 V). Cálculos teóricos, llevados a cabo a nivel DFT (B3 P86/6‐31 G*), predicen una estructura C2h altamente distorsionada para 11 a. La molécula adopta una conformación en forma de doble mariposa para aliviar el impedimento estérico. Los cálculos sugieren que la transferencia de carga intramolecular asociada a la transición HOMO→LUMO es responsable de la banda de absorción observada por encima de 400 nm en el espectro electrónico. El catión radical 11 a.+ retiene la estructura C2h plegada predicha para la molécula neutra como la conformación más e