Nonlinear charge carriers in organic conjugated polymers

Abstract

In this work a procedure for the prediction of the nature, stability, thermal behaviour and mobility of charge carriers in organic polymers exhibiting &pi;&nbsp;conjugation is described on the basis of a simple semi-empirical n-electron model. These charge carriers are assumed to be charged solitons in polymers with degenerate ground state and charged polarons in those with non-degenerate ground state. On the basis of calculations on the dynamics of polyenes we explain in detail how the parameters of the model Hamiltonian can be determined. It is shown that energy levels in the gap due to the nonlinear quasiparticles can be calculated, at least qualitatively correctly, Further, a short review of simulations of the dynamics of the charge carriers in <em>trans</em>-polyacetylene is provided. For the first time we show theoretical spectra, calculated including electron correlations of negatively charged solitons in <em>trans-</em>polyacetylene (t-PA). Also for the first time an exact solution 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 the mobility of neutral solitons in <em>t</em>-PA is discussed, which is shown to start around 10K. while at 100K the solitons are found to be completely mobile in agreement with experiment. Further. for the first time the theoretical expressions are derived for the calculation of vibrational spectra from dynamic simulations. Finally it is shown how the procedure can be extended to other polymers, and how the stability of such polymers against oxygen can be studied with the help of more sophisticated methods.