Electric field dependent generation of geminate electron-hole pairs in a ladder-type π-conjugated polymer probed by fluorescence quenching and delayed field collection of charge carriers

We report on measurements of electric field induced fluorescence quenching Phi and optical charge generation eta by using the time-delayed-collection-field technique (TDCF). The material under investigation is the methyl-substituted ladder-type poly(para-phenylene) (MeLPPP), a pi-conjugated polymer characterized by low intrachain disorder. Fluorescence quenching Phi of up to 50% is observed. The field dependence of both Phi and eta is associated with the primary step in charge generation, i.e., exciton dissociation into geminate electron-hole pairs rather than their full dissociation into free charge carriers. This is at variance with the basic assumption in Onsager's theory of charge generation. (C) 2002 Elsevier Science B.V. All rights reserved.