Managing photoexcited states in conjugated polymers

Chain length dependence of the photoemission (fluorescence, phosphorescence, delayed fluorescence) and the respective life times of poly conjugated macromolecules is subject of controversy since long. An underlying question concerns coherence and extension/localization of the photoexcited states. Energy transfer within and between macromolecules as well as between sensitizers and macromolecules are relevant processes in systems to be used for displays or solar energy harvesting. In this context our recent work on photophysical characterization of pure oligo(fluorene)s and of the same oligomers containing just one fluorenone ("keto-defect") group is reviewed. Energy transfer between poly(fluorene)s and metal porphyrins is also covered. Triplet- triplet-annihilation opens a route to efficient noncoherent energy upconversion at ultralow excitation intensity (ca i Wcm^-2). Light from the red region (635-700 nm) of terrestrial sun-light is converted into the green region with ΔE≥0-5 eV.