Disorder-Order transitions in p-conjugated polymers - Anna Köhler

The aggregation of pconjugated materials significantly impacts on the photophysics, and thus on the performance of optoelectronic devices. Nevertheless, we know comparatively little about the laws governing aggregate formation of pconjugated materials from solution. In this talk, I shall compare, discuss and summarize how aggregates form for three different types of compounds, that is, homopolymers, donoracceptor type polymers and low molecular weight compounds. To understand how aggregates form, we employ temperature dependent optical spectroscopy, which is a simple yet powerful tool for such investigations. I shall discuss how optical spectra can be analysed to identify distinct conformational states and to obtain quantitative information on changes in the interchain coupling, the conjugation length and the oscillator strength upon aggregate formation. We find aggregate formation to proceed alike in all these compounds by a coiltoglobule like first order phase transition. Notably, the chain expands before it collapses into a highly ordered dense state. I will address the role of side chains and the impact of changes in environmental polarization.