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

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.