Temperature Induced Order-Disorder Transition in Solutions of Conjugated Polymers Probed by Optical Spectroscopy.

The aggregation of π-conjugated materials significantly impacts the photophysics and performance of optoelectronic devices. Nevertheless, little is known about the laws governing aggregate formation of π-conjugated materials from solution. In this Perspective, we 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 this end, we employ temperature-dependent optical spectroscopy, which is a simple yet powerful tool to investigate aggregate formation. We show how optical spectra can be analyzed to identify distinct conformational states. We find aggregate formation to proceed the same 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. The role of side chains and the impact of changes in environmental polarization are addressed.