Solvolytic ionisation of organic charge‐transfer complexes

Abstract

Most organic charge-transfer complexes, when dissolved in a solvent of low ionising-power, appear to exist almost entirely as neutral electrondonor-acceptor pairs. Such complexes involve very little transfer of charge in the ground state. This type of behaviour is even observed for complexes formed by the combination of electron donors of low ionisation potential with electron acceptors of high electron affinity which in the solid phase have a significant degree of ionic character 1. However, when such strongly interacting systems (or mixtures of their components) are dissolved in solvents of high ionising power, ionic species are formed. It is suggested that the driving force for this ionisation is simply the energy of solvation of the ions produced 2 . This may be represented as:where (AD)cT is the charge-transfer complex, and A-and D+ are the two ions formed by single electron transfer from the electron donor (D) to the electron acceptor (A).If the ionic products in solution are the result of solvation, it should be possible reversibly to change the position of equilibrium between the ionic and the neutral charge-transfer molecular species by altering the nature of the solvent.The absorption spectrum of an equimolecular mixture of N , N , N ' , N'tetramethyl-p-phenylenediamine (TMPD) and chloranil in acetonitrile is shown in Fig. l(a). The absorptions at 428,448 nm are assigned to the dianion of the hydroquinone derived from chloranil, and the bands with maxima at 568, 618 nm to TMPD+ 3. The broad, low-intensity band at 843 nm is the intermolecular charge-transfer band of the molecular complex 3 . On R. Foster and T.

Tuning the Electronic Structure of Graphene by an Organic Molecule

“…17,18 It is a strong electron acceptor with a large electron affinity that readily forms charge-transfer complexes in which it pulls electrons from neighboring metal atoms or molecules. 19,20 Although the neutral TCNE molecule presents no magnetic properties, its empty antibonding molecular orbitals are spin-polarized, which result in spin-polarized electronic density when they are occupied by electrons.…”

Novel spectrophotometric method for the determination of azithromycin in pharmaceutical formulations based on its charge transfer reaction with quinalizarin

“…According to Foster, 35 the decrease of specific bands in the infrared spectrum can be used to identify the site where, in the molecule, charge-transfer reaction occurs. The spectrum of the quinalizarin alone ( Figure 5A) presented some specific absorption bands at 1604 and 1582 cm -1 , which can be assigned to the stretching of the two C=O bonds present in its structure.…”

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“…DDQ is a π-acceptor which reacts instantaneously with basic nitrogenous compounds to form a chargetransfer complex of n-π type [13][14][15][16][17][18] . The spectrum of DDQ in the acetonitrile mixture exhibits an absorption band at 372 nm.…”