NONLINEAR CHARGE-CARRIERS IN ORGANIC CONJUGATED POLYMERS

In this work a procedure for the prediction of the nature, stability, thermal behaviour and mobility of charge carriers in organic polymers exhibiting pi conjugation is described on the basis of a simple semi-e mpirical pi-electron model. These charge carriers are assumed to be ch arged solitons in polymers with degenerate ground state and charged po larons in those with non-degenerate ground state. On the basis of calc ulations on the dynamics of polyenes we explain in detail how the para meters of the model Hamiltonian can be determined. It is shown that en ergy levels in the gap due to the nonlinear quasiparticles call be cal culated, at least qualitatively correctly. Further, a short review of simulations of the dynamics of the charge carriers in trans-polyacetyl ene is provided. For the first time we show theoretical spectra, calcu lated including electron correlations of negatively charged solitons i n trans-polyacetylene (t-PA). Also for the first time an exact solutio n for the Su-Schrieffer-Heeger Hamiltonian is derived in the adiabatic limit, exhibiting explicitely the dynamics of the electrons. From the results obtained with this procedure the temperature dependence of th e mobility of neutral solitons in t-PA is discussed, which is shown to start around 10K. while at 100K the solitons are found to be complete ly mobile in agreement with experiment. Further. for the first time th e theoretical expressions are derived for the calculation of vibration al spectra from dynamic simulations. Finally it is shown how the proce dure can be extended to other polymers, and how the stability of such polymers against oxygen can be studied with the help of more sophistic ated methods.