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

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 blue -> green Forster resonant energy transfer (FRET), with a Forster radius R-0bg=35 A. The red dye is instead excited by direct blue -> red FRET (R-0br=21 A) and by sequential blue -> green -> red FRET (R-0gr=31 A). 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.