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A number of organic compounds form charge-transfer complex, which are often described as electron-donor-acceptor complexes (EDA complexes). Typical acceptors are nitrobenzenes or tetracyanoethylene (TCNE). The strength of their interaction with electron donors correlates with the ionization potentials of the components.
Fig. 1. The parabolas of outer-sphere reorganisation energy of the system two spheres in a solvent. Parabola i: the charge on the first, transfer to the second, parabola f: the charge on the second, transfer to the first. The abscissa is the transferred amount of charge Δe or the induced polarization P, the ordinate the Gibbs free energy.
Tetracyanoquinodimethane (TCNQ) is an organic compound with the chemical formula (N≡C−) 2 C=C 6 H 4 =C(−C≡N) 2. It is an orange crystalline solid. This cyanocarbon, a relative of para-quinone, is an electron acceptor that is used to prepare charge transfer salts, which are of interest in molecular electronics.
This method was first developed by Benesi and Hildebrand in 1949, [2] as a means to explain a phenomenon where iodine changes color in various aromatic solvents. This was attributed to the formation of an iodine-solvent complex through acid-base interactions, leading to the observed shifts in the absorption spectrum.
This equation is characteristic of incoherent hopping transport, which takes place at low concentrations, where the limiting factor is the exponential decay of hopping probability with inter-site distance. [4] Sometimes this relation is expressed for conductivity, rather than mobility:
Outer sphere electron transfer can occur between chemical species that are identical except for their oxidation state. [4] This process is termed self-exchange. An example is the degenerate reaction between the tetrahedral ions permanganate and manganate:
In the 1950s, organic molecules were shown to exhibit electrical conductivity. Specifically, the organic compound pyrene was shown to form semiconducting charge-transfer complex salts with halogens. [14] In 1972, researchers found metallic conductivity (conductivity comparable to a metal) in the charge-transfer complex TTF-TCNQ.
The Yukawa–Tsuno equation, first developed in 1959, [1] is a linear free-energy relationship in physical organic chemistry.It is a modified version of the Hammett equation that accounts for enhanced resonance effects in electrophilic reactions of para- and meta-substituted organic compounds.