Chapter 12

High Field ESR Spectroscopy
of Conductive Polymers

By V.I. Krinichnyi

The principles of utilization of high-frequency (140 GHz) EPR spectroscopy in the study of various conductive polymers (CP) are described in this Chapter. It starts with the Introduction, following by the paragraphs in which the magnetic parameters of charge carriers in CP, relaxation and dynamics of charge carriers in slightly doped CP and the charge transfer in highly doped CP are discussed. The high field saturation transfer ESR and spin probe methods in the study of CP are presented as well. Spin and spinless non-linear excitations was shown to exist as charge carriers in organic conductive polymers. With the increase of doping level the tendency of collapse of polaron pairs into diamagnetic bipolaron is observed. Conductivity in neutral or weakly doped samples is defined mainly by isoenergetic charge tunneling, which is characterized by a high enough interaction of spins with several phonons of a lattice and leads to the correlation of Q1D spin motion and interchain charge transfer. This mechanism ceases to dominate with the increase of a doping level and the charge can be transferred by its thermal activation from widely separated localized states in the gap to close localized states in the tails of the valence and conducting bands. Therefore, complex quasi-particles, namely the molecular-lattice polarons are formed in some polymers because of libron-phonon interactions analogously to that it is realized in organic molecular crystals. In heavily doped samples the dominating is the interchain Mott charge transport, characterized by strong interaction of charge carriers with lattice phonons. A higher spectral resolution at D-band ESR provides a higher accuracy of the measurement of magnetic resonance parameters, so then makes g-factor of organic free radicals an important informative characteristic. This allows the establishment of the correlation between the structure of organic radicals and their g-tensor canonic values, providing the ability of PC identification in conductive polymers and other solids. The high field ESR spectroscopy allows obtaining qualitatively new information on spin carrier and molecular dynamics as well as on the magnetic and relaxation properties of polymer systems.


1. Introduction


2. Magnetic Parameters of Charge Carriers in Conductive Polymers


3. Relaxation and Dynamics of Charge Carriers in Slightly Doped Conductive Polymers


4. Charge Transfer in Highly Doped Conductive Polymers


5. High-Field Saturation Transfer ESR Method in the Study of Conductive Polymers


6. High-Field Spin Probe Method in the Study of Conductive Polymers


7. Concluding Remarks