Intrachain Aggregates as the Origin of Green Emission in Polyfluorene Studied on Ensemble and Single-Chain Level

Polyfluorenes are conjugated polymers that show strong blue emission and as such have been explored for potential applications in light-emitting devices. However, heat treatment, prolonged exposure to air, or extended operation in electroluminescent devices can lead to an appearance of parasitic green emission that degrades the material performance. This phenomenon has been extensively studied over the past two decades, and two main and conflicting explanations, i.e., oxidation and formation of fluorenone species on the one hand and inter- or intrachain aggregation on the other, have been put forward. There is abundant experimental evidence to support either of these theories, and the question is far from settled. Here, we aim at getting deeper insight into the problem of the green emission origin using single-molecule spectroscopy performed on individual chains of poly(9,9-di-n-octylfluorene) (PFO) to resolve the green emission band and reveal its spectral and temporal heterogeneity. We disperse single P...