Solvatochromic effects on the photoinduced charge-transfer states in donor-acceptor substituted polydioctylfluorenes

Polymer morphology affects quantum efficiency. The influence of polymer morphology on the emission from charge transfer states within donor-acceptor (D-A) polydioctylfluorene derivatives is investigated. Two D-A copolymers, comprising one- and two-electron-donating triphenylamines substituted into the electron-accepting dioctylfluorene repeat unit were studied. Time-resolved emission spectra (with a resolution of 330 fs) in both liquid and glass phase isolate nuclear relaxation to the large-amplitude motion of the triphenylamine moiety about the single bond, analogous to the twisted intramolecular charge-transfer (TICT) model. The charge separation in the polymers' emitting states is therefore increased, suggesting a potential approach to enhance quantum efficiency in devices otherwise limited by exciton recombination. Tune up: Charge separation in polymer emitting states can be increased by choosing the right substituents for the photoactive polymer (see picture). This approach will enhance quantum efficiency in devices otherwise limited by exciton recombination.