On the Origin of Green Emission Bands in Fluorene-Based Conjugated Polymers

摘要

Blue-light-emitting diodes made of polyfluorenes have low stability and, under operation, rapidly degrade and produce undesirable low-energy emission bands (green or g-bands). A spectroelectrochemical study of the degradation process suffered by polyfluorenes is reported here. These polymers lose their electronic properties by electrochemical oxidation and reduction through σ-bond breaking. In addition, upon electrochemical reduction, the development of a structured green emission band at 485 nm is observed. The position and shape of this band is different from the usual featureless band at 535 nm assigned to fluor-enone defects. The green-light-emitting product is isolated and analyzed by Fourier-transform IR spectroscopy; fluorenone formation is excluded. The isolated product is crosslinked; its green emission is probably related to the formation of an intramolecular excimer.