Highly Conjugated p‐Quinonoid π‐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).

Electronic Interactions in a New π‐Extended Tetrathiafulvalene Dimer

“…To relieve the short contacts between the sulfur atoms and the hydrogen atoms in the peri positions, the central ring of the anthracene unit folds in a boat conformation and the molecule adopts a butterfly-or saddle-like structure, in which the benzene rings point upwards and the dithiole rings point downwards. The conformation calculated for 12 is similar to that obtained for unsubstituted exTTF [3,22] and is consistent with the crystal structures observed for different derivatives. [2b, 8d, 20a, 23] Each exTTF unit in compound 14 adopts a butterfly structure similar to that predicted for 12.…”

“…The molecular geometries of 12C + and 12 2 + were also optimized at the B3P86/6-31G* level for comparison purposes. Similarly to that previously found for unsubstituted exTTF, [3,22] 12C + preserves the butterfly-shaped structure of the neutral molecule, while 12 2 + adopts an orthogonal conformation in which the dithiole rings lie perpendicular to the central anthracene unit, which is fully planar.…”

The butterfly effect in bisfluorenylidene-based dihydroacenes: aggregation induced emission and spin switching

“…For example, acenes with a buttery structure were originally studied a couple of decades ago, and the buttery structure can be changed to a at structure by electrochemical oxidation. [18][19][20][21] Through precise molecular engineering of the core structure of oligoacenes, Tang and co-workers have shown that quinoidal derivatives of oligoacenes can exhibit aggregation induced restricted intramolecular vibration (RIV). 22,23 AIE is counterintuitive since aggregation tends to quench photoluminescence of organic chromophores.…”

Solid Film versus Solution‐Phase Charge‐Recombination Dynamics of exTTF–Bridge–C60 Dyads

“…The use of tetrathiafulvalene and p-extended tetrathiafulvalene (exTTF) units is based on their strong electron-donating character and their thermodynamic stability when oxidised, which stems from the gain in aromaticity of the dicationic species. [24][25][26][27][28][29][30][31][32][33] Moreover, careful design of the molecular dyads has enabled us to prepare moieties with long alkyl side chains attached to the molecular bridge to allow high solubility in organic solvents for both systems. Furthermore, dyad 1 possesses a binaphthyl unit as molecular bridge, which breaks the molecular conjugation between donor and acceptor moieties.…”