Molecular and Electronic Structures of the Long-Bonded π-Dimers of Tetrathiafulvalene Cation-Radical in Intermolecular Electron Transfer and in (Solid-State) Conductivity

Abstract

Tetrathiafulvalene (TTF) as the prototypical electron donor for solid-state (electronics) applications is converted to the unusual cation-radical salt, TTF+* CB- (where CB- is the non-coordinating closo-dodecamethylcarboranate), for crystallographic and spectral analyses. Near-IR studies establish the spontaneous self-association of TTF+* to form the diamagnetic [TTF+,TTF+] dication and to also undergo the equally rapid cross-association with its parent donor to form the mixed-valence [TTF+*,TTF] cation-radical. The latter, most importantly, represents the first (dyad) member of a series of p-doped tetrathiafulvalene (stacked) arrays, and the thorough scrutiny of its electronic structure with the aid of Mulliken-Hush (two-state) analysis of the diagnostic (intervalence) NIR band reveals Robin-Day Class II behavior. The theoretical consequences of the unique structure of the mixed-valence [TTF+*,TTF] dyad on (a) the electron-transfer mechanism for self-exchange, (b) the molecular-orbital analysis of the Marcus reorganization energy, and (c) the ab initio computation of the coupling element or transfer integral in p-doped (solid-state) arrays are discussed.

Direct Observation of Mixed‐Valence and Radical Cation Dimer States of Tetrathiafulvalene in Solution at Room Temperature: Association and Dissociation of Molecular Clip Dimers Under Oxidative Control

“…These NIR absorption bands are characteristic of mixed-valence and radical cation-radical cation dimer states, respectively, for pairs of stacked TTF units. [8][9][10]17] These spectra suggest the sequential formation of the tricationic dimer www.chemeurj.org (830 nm). This observation suggests that the stacking of more than two TTF radical cations in this dimer shifts the absorption band toward longer wavelengths; that is, the characteristic absorption of four continuously stacked TTF radical cations in this system is approximately 946 nm.…”

“…Recently, an elegant approach was developed to meet this challenge through the formation of a unique TTF + CCB À salt (CB = permethylcarboranyl), which forms mixed-valence dimers with neutral TTF and dimerizes at high concentrations. [10] Mixed-valence dimers [(TTF) 2 ]C + and radical cation dimers [(TTF) 2 ] 2 C 2+ exist in solution at low concentration only when the intermolecular interactions between the two constituents are sufficiently strong. Clipshaped molecules form complexes efficiently with a range of aromatic guest units; [11] this feature endows them with the potential to dimerize (Figure 1).…”

Hybrid Molecular Compound Exhibiting Slow Magnetic Relaxation and Electrical Conductivity

“…This absorption peak is evidence for a radical in (1), which agrees with the total charge of 0.81 electrons estimated from the crystal structure. In the higher energy region, the absorption peak at 461 nm was ascribed to a π-π* transition of BEDT-TTF +• [22,23].…”

“…This absorption peak is evidence for a radical in (1), which agrees with the total charge of 0.81 electrons estimated from the crystal structure. In the higher energy region, the absorption peak at 461 nm was ascribed to a π-π* transition of BEDT-TTF +• [22,23]. In order to investigate the electronic structure of (1), polarized IR reflectance spectra were acquired at 300 K. The spectra were polarized along the BEDT-TTF stacking direction, and the electrical vector was parallel to the [110] direction ( Figure 4).…”

Reversible Spin Pairing in Crystalline Organic Radicals

“…Variable temperature UV/vis and EPR spectroscopies have been used to probe the enthalpy and entropy for dimerisation processes for a number of radicals and selected values are presented in Table 8.1. [3][4][5][6][7][8] The temperature dependence of their spectroscopic properties can be quite marked, as illustrated in Figure 8.1 for PhCNSSN • . The λ max for isolated monomers falls in the UV region of the spectrum leading to a pale yellow colour at ambient temperature (due to a tail of λ max encroaching into the visible).…”