Charge-transfer complexes from tetracyanoquinodimethane

El-Brashy [51] reported the determination of primaquine and other antimalarials via charge-transfer complexes. Powdered sample of primaquine phosphate was dissolved in water and the solution was adjusted to an alkaline pH with 6 M ammonia and extracted with chloroform. The extract was dried with anhydrous sodium sulfate, filtered, and evaporated to dryness under nitrogen and the residue was dissolved in acetonitrile. Portions of the solution were mixed with 0.2% 7,7,8,8-tetracyanoquinodimethane, diluted with acetonitrile, and set aside for 10 min before the absorbance was measured at 845 nm versus a reagent blank. The calibration graphs were linear from 0.4 to 3 pg/mL and recovery was 98%. 

Figure 4.15 Electron affinities of charge transfer complex acceptors calculated from C2 = 2.9 versus the current best adiabatic electron affinities. This is a precision and accuracy plot. The zero intercept slope indicates that the same quantities are measured. The compounds are maleic anhydride, tetrachlorophthalic anhydride, benzoquinone, trinitro-flourenone, s-trinitrobenzene, chloranil, tetracyanoquinodimethane, and tetracyanoethylene in order of their electron affinities.

Full details have been published of the substitution reactions which result from irradiation of the charge-transfer complexes of 1,2,4,5-tetracyanobenzene and toluene81 and of 7,7,8,8-tetracyanoquinodimethane and toluene.82 The former reaction yields 1-benzyl-2,4,5-tricyanobenzene (44) via, it is suggested, the intermediate 1,4-acyclic adduct (45), and this reaction is quenched by trifluoro-acetic acid. In contrast, the formation of aa-dicyano-4-dicyanomethylbibenzyl... 

Tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE) are known to be strong electron acceptors, and the investigation of their properties is of interest since a number of stable charge transfer complex orystals with high electrical conductivities can be formed from them using a variety of electron donors. 

An epoch-making discovery in heterofulvene chemistry was the metallic conductivity in the charge-transfer complex formed from tetrathiafulvalene (TTF) 24 and tetracyanoquinodimethane (TCNQ) 25 in 1973 [12]. Upon this discovery, various functional dyes have been designed and constructed on the basis of electronic character of TTF however, this chapter only describes the functional dyes involving a fulvene moiety, because TTF chemistry is considerably larger (see Chapter 8) and many good books and reviews have already been published to date [13]. For the same reason, this chapter does not refer to the chemistry of porphyrins 26 and boron dipyrromethenes (BODIPY) 27, although they formally possess azafulvene moieties in their n-systems [14, 15]. 

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