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Managing Photoexcited States in Polyconjugated Macromolecules

The application of polymers for light emitting devices (“OLEDs”) and light harvesting systems (“solar cells”) has triggered rejuvenation of research on the properties of photo-excited states in macromolecules and their blends with organic chromophores. This presentation deals with fundamental features of such systems covering:

 1. Precisely defined oligomers of 9,9’-di(ethylhexyl)-fluorene for demonstrating the evolution of singlet and triplet states as function of molecular size. Life-times studies support that the photo-excited state extends coherently over the whole molecule (and macromolecule). A single keto-group per molecule leads to efficient energy localization at the keto-defect.

2. Delayed fluorescence is achieved by doping with triplet-energy harvesting chromophores. This allows for “up-conversion” of photo-energy via triplet-triplet energy transfer and has been optimized choosing the right match of components: a) chromophores which absorb in the red while showing efficient intersystem crossing to a long-lived triplet state and b) emitters which exhibit a singlet state which is addressed by triplet-triplet annihilation. Conversion of red to green or even blue light is demonstrated.

3. Application of these effects for novel devices will be discussed.