Disorder-Order Transitions in p-Conjugated Polymers
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The aggregation of p-conjugated 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 p-conjugated materials from solution. In this talk, I shall compare, discuss and summarize how aggregates form for three different types of compounds, that is, homopolymers, donor-acceptor 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 inter-chain coupling, the conjugation length and the oscillator strength upon aggregate formation. We find aggregate formation to proceed alike in all these compounds by a coil-to-globule 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.