CT-EXCITONS AND MAGNETIC-FIELD EFFECT IN POLYDIACETYLENE CRYSTALS

A new method aimed at the estimation of an electron-hole exchange interaction distance in organic and possibly other semiconductors is developed. It is based on studying the temperature dependence of the spin magnetic field effect on the photoconductivity. Photoexcitation of the polydiacetylene single crystal which is a quasi-one-dimensional semiconductor is shown to result in an appearance of delocalized on 70 angstrom intermolecular charge transfer states the latter being precursors of free charge carriers, The energy of the CT states is estimated to be 0.12 eV below a conduction band. Spin evolution in the correlated electron-hole pair is shown to proceed when the e-h distance is up to 1600 angstrom.