Abstract
Poly(9,9-dioctylfluorene) (PFO) is a blue-light-emitting polymer exhibiting two distinct phases, namely, the disordered "glassy" phase and a more ordered β-phase. We investigate how a systematic increase in the fraction of β-phase present in PFO films controls chain conformation, photoluminescence quantum efficiency (PLQE), and the resonant energy transfer from the glassy to the β-phase. All films are prepared by the same technique, using paraffin oil as an additive to the spin-coating solution, allowing systematic tuning of the β-phase fraction. The PFO films exhibit high PLQE with values increasing to 0.72 for increasing fractions of β-phase present, with the β-phase chain conformation becoming more planar and including more repeat units. Differences in Förster radii calculated from the overlap of steady-state absorptance and emission spectra and from time-resolved ultrafast photoluminescence transients indicate that exciton diffusion within the glassy phase plays an important role in the energy transfer process.
Highlights
Poly(9,9-dioctylfluorene) (PFO) is a blue-light-emitting polymer exhibiting two distinct phases, namely, the disordered “glassy” phase and a more ordered β-phase
In this Letter, we explore how the fraction of β-phase chains present in PFO thin films affects the nature of the electronic states, the chain conformation, photoluminescence quantum efficiency (PLQE), and the Förster resonant energy transfer (FRET) from glassy to β-phase chain segments
By comparing the values obtained from the two different methods, we find that the Förster radius is enhanced by exciton diffusion within the glassy phase occurring prior to energy transfer
Summary
Letter changes in the energy transfer mechanisms,[23,24,26] and their potential interplay.[29]. The Förster radius derived from these data takes into account both γ and the concentration of β-phase chain segments in the films, resulting in the slightly decreasing trend for R0 with increasing β-phase content displayed in Figure 4 (blue open squares) To assess how these Förster radii compare with those expected from Förster’s theory of resonance energy transfer, we used the following expression to calculate R0 from the overlap between the donor emission and the acceptor absorption:[32,48]. With increasing β-phase content, the emission peaks of the β-phase red-shift and narrow, while the associated Huang−Rhys factor decreases These findings suggest that the conformation of βphase segments changes with increasing fraction, adopting a more planar structure and/or including a larger number of repeat units. Experimental procedures, and detailed results for absorption spectra and determination of β-phase content, time-integrated photoluminescence spectra, photoluminescence quantum efficiency, lifetimes and decay rates, Förster radii (PDF)
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