Electric field-induced fluorescence quenching and transient fluorescence studies in poly(p-terphenylene vinylene) related polymers

Electric field induced fluorescence quenching has been investigated for a series of poly(p-terphenylene vinylene)s. The quenching efficiencies follow a strictly quadratic dependence on the applied field amplitude with maximum values of about 10% at 200 V/mu m. Quenching occurs predominately at higher emission energies, resulting in a distinct blue-shift between the electro-modulated signal and the photoluminescence spectra. These results provide evidence for the field assisted dissociation of neutral excitons within an inhomogeneously broadened density of states (DOS). Experiments are also performed on devices prepared by the Langmuir-Blodgett-technique in order to evaluate contributions by the Stark effect. These experiments prove the electric field-assisted separation of charges onto separate chains. Transient photoluminescence experiments show fluorescence decay times ranging between 100 ps and 200 ps. The increase in relaxation times for larger detection wavelengths gives evidence for spectral relaxation within the DOS. This leads to a consistent picture, where the balance between electric field assisted dissociation of excitons competes with the radiative decay as well as the non-radiative decay processes. Implications on the spectral properties of electroluminescent devices are further discussed. (C) 1998 Elsevier Science B.V.