Tetracyanoquinodimethane electron affinity

Compton RN, Cooper CD (1977) Negative ion properties of tetracyanoquinodimethan electron affinity and compound states. J Chem Phys 66 4325 1329... 

Through reduction or oxidation of the molecule by a dopant molecule. Atoms or molecules with high electron affinity, such as iodine, antimony pentafluoride (SbCls), or 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), may oxidize a typical organic semiconductor such as poly(p-phenylene) derivatives, leaving them positively charged. Reduction, i.e., addition of an electron, may be obtained by doping with alkali metals. 

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.

In the case of tetracyanoquinodimethane, carbon disulfide, nitromethane, and the purines and pyrimidines, two or more negative-ion states have been observed. In some cases the photoelectron spectrum can be assigned to an excited state and reveal an electron affinity lower than adiabatic electron affinity. In the case of cyclooctatetraene the onset in the PES spectrum is higher than adiabatic electron affinity because of the significant change in the geometry of the anion. 

Certain organic molecules, e.g. 7,7,8,8,-tetracyanoquinodimethane TCNQ can accept electrons and form free anion radicals stable at room temperature. Concentrations of TCNQ and TCNQ radical can be determined using ESR, or even assessed on the basis of coloration. Meguro and Esumi [345] proposed a method to determine acid base properties of solid surfaces from radical concentration in the surface layer for a series of electron acceptors having different electron affinities. In this method a tacit assumption is made that except for the studied absorbent and TCNQ/TCNQ radical there are no other electron acceptors or donors in the system, which is not necessarily correct. This problem is analogous to assessment of acid base properties of materials based on their electrokinetic potentials in allegedly pure organic solvents (Section V). 

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