A Fully Conjugated TTF–π–TCAQ System: Synthesis, Structure, and Electronic Properties

Abstract

The synthesis of the first fully conjugated tetrathiafulvalene-tetracyano-p-quinodimethane ((TTF)-TCNQ)-type system has been carried out by means of a Julia-Kocienski olefination reaction. In particular, a tetracyanoanthraquinodimethane (TCAQ) formyl derivative and two new sulfonylmethyl-exTTFs (exTTF = 2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole)--prepared as new building blocks--were linked. A variety of experimental conditions reveal that the use of sodium hexamethyldisilazane (NaHMDS) as base in THF afforded the E olefins with excellent stereoselectivity. Theoretical calculations at the B3LYP/6-31G** level point to highly distorted exTTF and TCAQ that form an almost planar stilbene unit between them. Although calculations predicted appreciable electronic communication between the donor and the acceptor, cyclic voltammetric studies did not substantiate this effect. It was only in photophysical assays that the electronic communication emerged in the form of a charge-transfer (CT) absorption and emission. Once photoexcited (i.e., the locally excited state or excited charge-transfer state), an ultrafast, subpicosecond charge separation leads to a radical ion pair state in which the spectroscopic features of the radical cation of exTTF as well as the radical anion of TCAQ are discernable. The radical ion pair is metastable and undergoes a fast ((1.0±0.2) ps) charge recombination to reconstitute the electronic ground state. Such ultrafast charge separation and recombination processes come as a consequence of the very short vinyl linkage between the two electroactive units.

Donor‐π‐Acceptors Containing the 10‐(1,3‐Dithiol‐2‐ylidene)anthracene Unit for Dye‐Sensitized Solar Cells

“…Identical MO topologies are obtained for the isolated dye in the gas phase. The HOMO (−5.14 eV) is mainly localized on the electron‐donor dithiol unit and is calculated at lower energy than the HOMO of the tetramethylthio–exTTF molecule (−4.90 eV), which contains two dithiol units 14. The HOMO−1 (−5.75 eV) spreads over the dithiol and the diacetylene units and is separated by 0.64 eV from HOMO−2 (−6.39 eV), which is fully localized over the acceptor part of the molecule.…”

A Straightforward Electroactive π‐Extended Tetrathiafulvalene (exTTF) Building Block

“…In a first approach, we have recently reported the synthesis of a series of exTTFs bearing a sulfone reactive group ( 4 ) and their further Julia–Kocienski reaction with aldehydes (Figure 1). 13 Although formation of the product proceeds reasonably well in moderate to good yields, formation of the starting sulfone was found to be a somewhat capricious reaction that occurs in relatively low yields, thus preventing the use of these sulfones as general starting materials for further chemical modifications.…”

Covalent non-fused tetrathiafulvalene–acceptor systems

“…17 Because of some synthesis issues, it took more than twenty years after this theoretical prediction for covalently linked TTF-TCNQ or TTF-TCNAQ (TCNAQ = tetracyanoanthraquinodimethane) compounds to be described and properly characterized. Some of the first such examples consist of TTF-TCNAQ systems 2 and derivatives, as reported by Bryce et al, 18 and 3, as reported by Liu et al, 19 while in compound 4, as described by Martin et al, 20 TTF was replaced by extended-TTF (ext-TTF) and a conjugated linkage between the two units was preserved. Both flexible 5 and rigid 6 TTF-s-TCNQ systems possessing small HOMO-LUMO gaps were described by Bryce and Perepichka et al 21 and Khodorkovsky et al, 22 respectively.…”