Charge-transfer complex

[4] Early studies on donor-acceptor complexes focused on the solvatochromism exhibited by iodine, which often results from I2 forming adducts with electron donors such as amines and ethers.

The CT interaction has been quantified and is the basis of many schemes for parameterizing donor and acceptor properties, such as those devised by Gutmann, Childs,[6] Beckett, and the ECW model.

In solution, the intensity of charge-transfer bands in the UV-Vis absorbance spectrum is strongly dependent upon the degree (equilibrium constant) of this association reaction.

[8] In the solid state a valuable parameter is the elongation of the X–X or X–Y bond length, resulting from the antibonding nature of the σ* LUMO.

[11] A well-known example is the complex formed by iodine when combined with starch, which exhibits an intense purple charge-transfer band.

[4] In 1973, it was discovered that a combination of tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) forms a strong charge-transfer complex referred to as TTF-TCNQ.

Examples include electrophilic aromatic substitution, the addition of Grignard reagents to ketones, and brominolysis of metal-alkyl bonds.

Structure of one part of one stack of the charge-transfer complex between pyrene and 1,3,5-trinitrobenzene. [ 1 ]
Edge-on view of portion of crystal structure of hexamethylene TTF /TCNQ charge transfer salt, highlighting the segregated stacking. [ 12 ]
End-on view of portion of crystal structure of hexamethylene TTF /TCNQ charge transfer salt. The distance between the TTF planes is 3.55 Å.