Effect of Polycations Containing Aromatic Heterocyclic Compounds on the Conductivity of Their TCNQ Salts

Abstract

Several kinds of monomeric 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) complex salts were prepared from aromatic cations. Polycations were obtained from the polymer reaction of poly(epichlorhydrine) (PEH) with aromatic heterocyclic amines, and their TCNQ salts were prepared. The effect of the cation structure on the electronic conductivities of the TCNQ salts is discussed, noting the interplay of steric and polarizability effects. The conductivity of the TCNQ salts increases with an increase of the longest wavelength absorption (λmax) of the ammonium iodides, which can be a guide in estimating the polarizability of cations. In the monomeric TCNQ complex salts, it is found from the X-ray diffraction analysis that the crystal structure is affected by the change of the cation structure. Thus, the conductivity is affected by the steric factor as well as by the polarizability. In the polycation—TCNQ salts, however, the morphological change is considered to be small, because their X-ray diffraction patterns are similar. Thus, the increase of conductivity results from the increase of polarizability of the polycations by decreasing the Coulomb repulsion between carrier electrons, since the steric factor is unchanged.