Insights into the origins of inverted circular dichroism in thin films of a chiral side chain polyfluorene

We synthesized a fluorene-bithiophene co-polymer with chiral side chains(cPFT2) and investigated its chiroptical properties via synchotronradiation cir-cular dichroism. We observed that thin films of the polymer display an intensecircular dichroism (CD) upon annealing, which is of opposite handedness tothe CD reported for similar polyfluorenes bearing the same enantiomericchiral side chain. We then contrast the properties of this polymer with chiralside chain fluorene homopolymer (cPF) and observe large differences in theirthin film morphology. Using photoluminescence spectroscopy, we uncoverevidence of polymer chain bending incPFT2, which is further supported bytheoretical calculations, and propose an explanation for the observed invertedoptical activity.