Spectroscopic properties of poly(9,9-dioctylfluorene) thin films possessing varied fractions of β-phase chain segments: enhanced photoluminescence efficiency via conformation structuring.
Poly(9,9-dioctylfluorene) (PFO) is a widely studied blue-emitting conjugated polymer, the optoelectronic properties of which are strongly affected by the presence of a well-defined chain-extended "β-phase" conformational isomer. In this study, optical and Raman spectroscopy are used to systematically investigate the properties of PFO thin films featuring a varied fraction of β-phase chain segments. Results show that the photoluminescence quantum efficiency (PLQE) of PFO films is highly sensitive to both the β-phase fraction and the method by which it was induced. Notably, a PLQE of ∼69% is measured for PFO films possessing a ∼6% β-phase fraction induced by immersion in solvent/nonsolvent mixtures; this value is substantially higher than the average PLQE of ∼55% recorded for other β-phase films. Furthermore, a linear relationship is observed between the intensity ratios of selected Raman peaks and the β-phase fraction determined by commonly used absorption calibrations, suggesting that Raman spectroscopy can be used as an alternative means to quantify the β-phase fraction. As a specific example, spatial Raman mapping is used to image a mm-scale β-phase stripe patterned in a glassy PFO film, with the extracted β-phase fraction showing excellent agreement with the results of optical spectroscopy. © 2016 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2016,54, 1995-2006.
Department of Materials Eidgenössische Technische Hochschule (ETH) Zürich Vladimir-Prelog-Weg 5 Zürich 8093 Switzerland; Department of Physics and Centre for Plastic Electronics Imperial College London, South Kensington Campus London SW7 2AZ United Kingdom.
Aleksandr
A
Perevedentsev
Department of Physics and Centre for Plastic Electronics Imperial College London, South Kensington Campus London SW7 2AZ United Kingdom.
Nathan
N
Chander
Department of Physics and Centre for Plastic Electronics Imperial College London, South Kensington Campus London SW7 2AZ United Kingdom.
Ji-Seon
JS
Kim
Department of Physics and Centre for Plastic Electronics Imperial College London, South Kensington Campus London SW7 2AZ United Kingdom; Engineering Science and Physics Departments, Mathematical, Physical and Life Sciences Division University of Oxford 9 Parks Road Oxford OX1 3PD United Kingdom.
Donal D C
DD
Bradley
conformation; conjugated polymers; microstructure; polyfluorene; spectroscopy