(Georgia Institute of Technology, 2016-12-02)
Köhler, Anna
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.