Face-to-Face Dimeric Tetrathiafulvalenes and Their Cation Radical and Dication Species as Models of Mixed Valence and π-Dimer States

Abstract

Intramolecular interactions of face-to-face tetrathiafulvalenes (TTFs) in 1,8-bis(tetrathiafulvalenyl)naphthalene frameworks were investigated in neutral and cationic states. From X-ray analysis and NMR spectroscopy on neutral 1,8-bis(tetrathiafulvalenyl)naphthalenes, which exist as a mixture of syn-and anti-isomers in solution, there is steric repulsion between TTF moieties. However, analysis of the cyclic voltammogram (CV) revealed that a strong attractive interaction was present in the cation radical state. Electronic spectra of the cation radical state showed the presence of a mixedvalence (MV) state with a strong charge resonance feature. ESR spectra of the 1,8-bis(tetrathiafulvalenyl)naphthalene cation radical showed a typical signal of an MV state. Furthermore, a ³-dimer, which exhibits pronounced Davydov splitting in the electronic spectra, was formed in the dication state. The observed absorption bands in the electronic spectra were characterized by using quantum chemical calculations of the cation radical and dication species. NMR spectra of both the ³-dimer and tetracation species show either a deshielding effect due to cationic charge or a shielding effect due to diamagnetic ring currents. To our knowledge, this is the first reported example of a 1 H NMR spectrum of TTF ³-dimer.Tetrathiafulvalene (TTF) and its derivatives can be easily oxidized to form stable cation radicals and dications, and these cationic species have been employed extensively in the development of new organic metals, superconductors, and semiconductor devices.

Engineering Dendritic Aptamer Assemblies as Superior Inhibitors of Protein Function

“…Hasegawa et al. prepared compounds 26 a – c in which the two TTF units are appended to the naphthalene ring in a face‐to‐face way 39. When the two TTF units were oxidized to TTF ⋅+ in a 1:1 mixture of dichloromethane and acetonitrile, strong intra‐molecular π‐stacking was exhibited for the two TTF ⋅+ units, as evidenced by the appearance of a typical absorption band around 732 nm in the UV/Vis spectrum.…”

Steric Control in the π‐Dimerization of Oligothiophene Radical Cations Annelated with Bicyclo[2.2.2]octene Units

“…[3] Since then, the p-dimer of oligothiophenes has attracted much attention to elucidate the electronic structure and conduction mechanism of p-doped polythiophenes. [4][5][6][7][8][9][10][11][12][13][14][15] A similar p-dimerization was also observed and studied both experimentally and theoretically in other stable radical-species, such as tetrathiafulvalene (TTF) radical cations, [16] phenalenyl radicals, [17] tetracyanoethylene (TCNE) radical anions, [17c, 18] tetracyanoquinodimethane (TCNQ) radical anions, [18d, 19] and viologen radical cations. [20] Experimental studies conducted thus far on the p-dimers of oligothiophene radical cations have revealed chain-length dependence [5] and solvent effects [6] on p-dimerization in the solution phases and the structures of the p-dimer in crystalline form.…”

Synthesis, Structure, Optical, and Electrochemical Properties of Triple‐ and Quadruple‐Decker Co‐facial Tetrathiafulvalene Arrays

“…This splitting of the longest absorption band in the spectrum is a typical feature of face‐to‐face arrays of the TTF . + components . As the electronic spectrum of 3Ma 4+ in the diluted solution ( c <10 −5 m ) exhibited almost identical spectral features in these cationic states, the intermolecular π‐dimeric species can be ruled out .…”

“…These attractive interactions have been found in many rigid dimeric systems, namely enforced TTF dimers. For an archetypal example of these systems, the cationic TTF dimer 1,8‐bis(tetrathiafulvalenyl)naphthalene 15 n + ( n =1, 2) (Scheme ) shows similar absorption for both the cation radical and dication species: an intensive CR band and remarkable Davydov shift were found as the result of the MV state and π‐dimer formation, respectively . Two cationic TTFs are stacked in face‐to‐face mode with a separation of 3.5–3.7 Å both in 15 .…”

“…Dimeric TTFs can be easily oxidized to a MV dimer upon one‐electron oxidation, and the resulting MV dimer is significantly stabilized by delocalization of the positive charge. This electronic structure is characterized by a charge resonance (CR) absorption band in the low energy region of the electronic spectra or distinctive hyperfine splitting in the ESR signal . When further oxidation takes place to form a dication, π‐dimers can form.…”