Synthesis, Properties, and Theoretical Characterization of Largely π-Extended Tetrathiafulvalene Derivatives with Quinonoid Structures

Abstract

A series of highly conjugated tetrathiafulvalene (TTF) analogues with a quinonoid structure has been synthesized, and their structural and electronic properties have been characterized by both experimental techniques and quantum-chemical calculations. Cyclic voltammetry measurements show a two-electron oxidation wave to form the dication, which is mainly located on the dithiole rings. The second irreversible oxidation wave to form the trication-radical corresponds to the oxidation of the polyacenic backbone. The temperature dependence of the reduction peak corresponding to the donor2+ → donor0 process is explained in terms of the low stability of the cation and the high aromaticity of the dication. Charge-transfer complexes are formed with the strong acceptor TCNQF4 showing a 1:2 (D:A) stoichiometry and a semiconducting behavior. The molecular structures of neutral and oxidized compounds are investigated by performing theoretical calculations at the semiempirical, ab initio, and density functional theory levels. The steric hindrance introduced by lateral benzoannulation determines the loss of planarity of the neutral molecules, which adopt butterfly shaped structures. The folded structures are retained in the cations, reducing the gain of aromaticity in the first oxidation step. The dications are by contrast predicted to be fully aromatic and are formed by a planar polyacenic moiety and two orthogonal, singly charged dithiole rings. The destabilization of the cations and the high aromaticity of the dications explain the redox properties observed experimentally. Theoretical calculations also help to rationalize the UV−vis data since they predict the appearance of a low-energy charge-transfer absorption band for the neutral compounds where the laterally fused polyacenic units act as acceptors.

Weighting non-covalent forces in the molecular recognition of C60. Relevance of concave–convex complementarity

“…1 shows the BH&H/6-31G** energy-minimized structures of the complexes and selected distances. The recognizing units in both 1 and 2 show butterfly-shaped conformations, consistent with previously reported structures, [12][13][14] in which the …”

Rates and energetics of intramolecular electron transfer processes in conjugated metallofullerenes

“…In stark contrast, the reductive range only reveals La 2 @C 80 reductions at −0.45, −1.73 and −2.23 V [29]. The redox potentials, as found for C 60 -exTTF, La@C 82 -exTTF and La 2 @C 80 -exTTF, reveal, in agreement with the data stemming from the corresponding references, namely C 60 [37], La@C 82 [40], La 2 @C 80 [41] and exTTF [32][33][34][35], only weak electronic interactions between the electron donors and electron acceptors in their ground state. Considering the exTTF centred oxidation and the lowest reduction of C 60 , La@C 82 and La 2 @C 80 , we derive radical ion pair state energies of 1.12 eV for C 60 -exTTF, 0.43 eV for La@C 82 -exTTF and 0.45 eV for La 2 @C 80 -exTTF (see below).…”

Hole‐Transfer Dyads and Triads Based on Perylene Monoimide, Quaterthiophene, and Extended Tetrathiafulvalene

“…The fact that only a two-electron oxidation is experimentally observed for this unit is attributed to the strong stabilization (gain in aromaticity) experienced by the dication upon planarization of the central polyacenic moiety. [68] Thus, the one-electron oxidation potential of exTTF is not known, except for the fact that it must be equal or higher than the experimental two-electron value. The observed disproportionation of the radical monocation, generated radiolytically [69] or by flash photolysis, [41] strongly suggests that the one-electron oxidation potential must be higher than the experimental two-electron value.…”