Optical absorption of the β‐phase of poly(9,9‐dioctylfluorene)

We outline a theory for the optical absorption of the β‐phase of poly(9,9‐dioctylfluorene) (PFO) that is based on the Frenkel exciton model. The absorption peak at 435 nm is attributed to polymer segments having torsion angles equal to π that are weakly perturbed by the presence of random monomer junctions with torsion angles equal to 0. The broad band below 435 nm is associated with disordered segments having a broad distribution of random torsion angles. The effects of small random deviations from π in the torsion angles are discussed. The calculations support the interpretation that the β‐phase is characterized by alternating segments of highly ordered and strongly disordered regions. PFO is a widely studied fluorene‐based polymer with interesting and potentially useful photophysical properties. In this work, Frenkel exciton states in the β‐phase of PFO are studied, and a two‐region model—weak torsional disorder and strong torsional disorder—is presented. The peak in the optical absorption at 435 nm is associated with the weakly disordered regions. The broad background in the absorption is attributed to the strongly disordered regions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1109–1111