Förster energy transfer mechanism and color tunability in three binary conjugated polymer blends

Abstract

The energy transfer mechanism from poly(9,9-dioctylfluorene-2,7-diyl) (PFO) to poly 9,9-dioctylfluorene-alt-benzothiadiazole (F8BT) and to poly(2-methoxy-5(2-ethylhexyl)-1,4 -phenylenevinylene (MEH-PPV), and from F8BT to MEH-PPV were comprehensively investigated. The concentrations of the donors in their binary blends were kept constant, while the acceptor concentration was carefully varied before reaching the complete emission quenching. The binary blend thin films were prepared using the solution blending method before they were spin-coated onto glass substrate. The UV–Vis absorption and emission spectra showed color emission shift towards the acceptor emission, confirming the energy transfer. These spectra were used to calculate important energy transfer parameters, such as the Förster radius (Ro), the distance between donor and acceptor molecules (RDA), energy transfer rate (kET), energy transfer efficiency (η), energy transfer probability (PDA), quenching constant (Ksv) and quenching rate constant (kq). The spectra also indicated that at high acceptor content the creation of excimer due to the molecule aggregation resulted in a red shift of the acceptor emission. In addition, the CIE coordinates proved the tunability of the color-emission. Finally, based on the calculated parameters, energy transfer mechanism in the three binary blends were suggested.