Phenothiazines charge-transfer complexes

It was mentioned in Section III,A, 1 that, as indicated by the results of quantum mechanical calculations, phenothiazine is an excellent electron donor the numerous examples in the previous subsections dealing with the oxidation of phenothiazines also illustrated the ease with which electrons are lost by the derivatives of this heterocycle. Consequently, phenothiazine charge-transfer complexes with various acceptors are expected. 

IV. Free Radicals, Cations, and Charge-Transfer Complexes within the Phenothiazine Class... 

As phenothiazine is a good electron donor, there are many papers on the interaction of this compound with various acceptors (see Sections III,A,1, and IV,H,1). In most cases, authentical charge-transfer complexes are obtained however, with very strong acceptors, e.g., 2,3-dichloro-5,6-dicyano-p-benzoquinone, (DDQ), there is total transfer of one electron, leading to It is possible that the same... 

A comparative survey of the electron-donor abilities of some phenothiazine derivatives in the formation of charge-transfer complexes clearly illustrated the lowering of the energy of the highest occupied level, that is, the decrease of the donor tendencies, with A-substitution (cf. Section III, A, 2). 

However, because the oxidized forms of the phenothiazine derivatives are good electron acceptors, phenazathionium salts with easily polarizable anions will be expected to have more or less pronounced charge-transfer complex character, the acceptor being in this case the phenazathionium cation. Both these types of charge-transfer complexes are actually known. 

Charge-Transfer Complexes of Phenothiazine and of Its Substitution Products... 

Very stable complexes, which may be sublimed and sometimes recrystallized, are obtained when the preparation of some phenothiazines by thionation is carried out using excess of iodine and sulfur. These complexes contain two, four, or six atoms of sulfur per phenothiazine residue, and their IR spectra are identical to those of the heterocyclic component, as expected of charge-transfer complexes. ... 

In a search for a mechanism of the inhibitory action exerted by chlorpromazine on some enzymatic processes, the interaction of this substance with oxidized flavines and xanthines was investigated, and the formation of charge-transfer complexes was observed. There are many indications that the phenothiazine-melanine interaction, which is probably involved in the retinotoxicity of some phenothiazine drugs, is also of the donor-acceptor type, as suggested... 

In earlier literature there are reports of the formation of perhalides on treatment of phenothiazine with bromine and iodine these are now considered to be charge-transfer complexes. The phenothiazine component normally acts as a donor and the electronegative halogens as acceptors, but here total transfer of electrons occurs and the phenothiazine is oxidized. Phenothiazine and 3,7-dimethylpheno-thiazine behave similarly in the presence of strong organic acceptors, like dicyanobenzoquinone and dichlorodicyanobenzoquinone. ... 

Chlorpromazine and other phenothiazine tranquilizers preferentially accumulate at sites of high melanin content such as hair and certain glandular tissues, and it has been suggested that this is based on an interaction possibly by formation of a charge transfer complex. In such an adduct chlorpromazine would function as an electron donor and melanin as an electron acceptor. ... 

A. Brau, J. P. Farges, and F. Gutmann, Electrochemical Studies of Phenothiazine-lodine Charge-Transfer Complexes, Electrochim. Acta 17, 1803-1811 (1972). 

Finally, the interaction of other cations such as alkali metal cations, the iron-sulfur cluster, and tropylium has been investigated in the presence of PPy films N-substituted with specific groups, namely ferrocene bisamide derivatives 31 [366], cystine [367], and phenothiazine [368]. The charge transfer complex produced between phenothiazine-substituted PPy and the tropylium cation was used in a photoelectrode device [368]. 

Phenothiazines are known to give rise to stable radical cations and dications [171-173] as well as to charge-transfer complexes. Phenothiazinyl-substituted ligands have been used in metal complexes to study electron-transfer processes [174-176]. Recently, Gompper and co-workers have reported the 1-phe-nothiazinyl-vinamidinium salt as a model for a molecular switch [177]. 

In complex (81), the electron-donating phenothiazine moiety is separated from the Ru(bpy)2 " unit by a triazole bridge that carries a formal negative charge. An investigation of this system shows that such anionic bridges can mediate electron transfer between chromophore and quencher. ... 

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