Optical studies of photoexcitations of poly(9,9-dioctyl fluorene)

We have studied the interplay between the morphology and photophysics of po ly(9,9-dioctyl fluorene) (PFO) films. Spin-casting from solution produces a glassy film with a broad absorption band and a large Stokes shift due to e xciton migration. Upon slowly warming a sample from 80 to 300 K, a fraction of the sample converts into a new phase with extended conjugation, which w e refer to as the P-phase. Its absorption band exhibits a clear vibronic st ructure, and the fluorescence red-shifts by approximately 0.1 eV. The photo induced absorption (PA) spectrum of the glassy phase is dominated by triple r excitons, whereas, both charged polarons and triplet excitons are seen in the PA spectrum of a sample containing both phases. (C) 2000 Published by Elsevier Science S.A. All rights reserved.