Intermolecular sequential energy transfer in thin films of a white emitting copolymer

Abstract

The authors investigated the energy transfer between the chromophors of a white emitting polyspirobifluorene copolymer containing a blue emitting backbone, a green, and a red emitting dye. They demonstrate that the green dye is mainly excited by $\text{blue}\to \text{green}$ Förster resonant energy transfer (FRET), with a Förster radius $R_{0\mathrm{bg}}=35\mathrm{\AA }$ . The red dye is instead excited by direct $\text{blue}\to \text{red}$ FRET $(R_{0\mathrm{br}}=21\mathrm{\AA })$ and by sequential $\text{blue}\to \text{green}\to \text{red}$ FRET $(R_{0\mathrm{gr}}=31\mathrm{\AA })$ . Finally, the authors show that the FRET processes, fundamental to have white emission, are of intermolecular nature, while intramolecular energy migration and transfer are negligible.