Structure analysis of conductive polymer systems: Poly-4-vinylpyridine and poly(butadiene-b-4-vinylpyridine) with 7,7′,8,8′-tetracyanoquinodimethane

Summary

The structure analysis of two conductive polymer systems-poly-4-vinylpyridine and poly(butadiene-b-4-vinylpyridine) with 7,7′,8,8′-tetracyanoquinodimethane (TCNQ)-was done by X-ray diffraction, scanning tunneling microscopy (STM) and FTIR. The charge transfer complex formed between the pyridine group and the known electron acceptor, TCNQ, is supposed to be the conductive element in these systems. In order to understand the structure of this complex, a model compound, the complex of 4-ethylpyridine (4EP) with TCNQ, 4EP/TCNQ₂, was studied by the mentioned methods. It appears that there are two crystalline modifications of the model compound with different type of stacks of the TCNQ molecules. In polymer systems only one type of the complex is dominant as revealed by joint analysis of X-ray diffraction diagrams, STM and FTIR data. In the STM image of the polymer surface one can distinguish that molecular stacks with periodicities of 4.1 Å in a row are separated (12.5Å) from each other. Such organization is similiar to the one observed in conductive charge transfer complexes such as tetrathiofulvalene (TTF) with TCNQ. The ordered molecular domains are scattered on the polymer surface and take part in the formation of the conductive network.