Hydrogen-bonding-assisted self-doping in tetrathiafulvalene (TTF) conductor.
The synthesis, characterization, and carrier generation mechanism of self-doping in a tetrathiafulvalene (TTF) conductor, ammonium tetrathiafulvalene-2-carboxylate (TTFCOO(-)NH(4)(+)), are described together with molecular orbital characteristics. Insulating TTFCOOH changes into a hole-doped conductor TTFCOO(-)NH(4)(+) with a conductivity of sigma = 2.0 x 10(-4) S/cm (300 K), upon salt formation with NH(3). A radical species, TTF(*+)COO(-)NH(4)(+), is generated via protonation of the TTF moiety as demonstrated by UV-vis, ESR, and (1)H NMR spectra. The X-ray crystallographic structure of TTFCOO(-)NH(4)(+) reveals supramolecular arrays of TTFCOO(-) moieties with short S...S contact, assisted by the one-dimensional hydrogen-bonding network composed of the ammonium and carboxylate ions. Molecular orbital calculations of cluster models show that the singly occupied molecular orbital (SOMO) of TTF(*+)COO(-)NH(4)(+) in the supramolecular array is not at the highest energy level, which is characterized as a quasi-closed-shell state. The ab initio periodic calculation with a one-dimensional boundary condition reveals that TTF(*+)COO(-)NH(4)(+) behaves as a dopant leading to the semiconducting behavior of the stacked TTF moieties assembled by the hydrogen-bonding network. Namely, TTFCOO(-)NH(4)(+) can be described as a "hydrogen-bonding-assisted self-doped conductor". The contribution of the hydrogen-bonding interaction to the electron conduction is experimentally supported by a large isotope effect in the ac conductivity of TTFCOO(-)NH(4)(+) at low temperature.
Kobayashi
Yuka
Y
Waseda Institute for Advanced Study, Waseda University, Tokyo, 169-8050, Japan. yuka@aoni.waseda.jp
Yoshioka
Mayu
M
Saigo
Kazuhiko
K
Hashizume
Daisuke
D
Ogura
Takashi
T
D018360:Crystallography, X-Ray; D004553:Electric Conductivity; D004563:Electrochemistry; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006573:Heterocyclic Compounds, 1-Ring / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure
D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; C544197:tetrathiafulvalene-2-carboxylic acid; C063887:tetrathiafulvalene