Multimodal Optical Analysis of Regioregular Poly(3-hexylthiophene)s Reveals Peculiar Aggregation Dynamics

The induction of polythiophene aggregation by decreasing the solvent quality is seen as a considerable technological advancement for organic optoelectronic applications. However, studying the sequence of molecular and supramolecular rearrangements upon aggregation remains highly challenging. Because the initial conformations significantly affect the end product in stochastic processes, understanding the initial stages of aggregation is of crucial importance for rational crystal engineering. To this end, a multimodal optical detection scheme was adopted, relying on extinction, spectrally resolved linear and nonlinear scattering, and fluorescence detection, allowing for the in situ characterization of the different stages of polymer aggregation. Specifically, our results indicate that the aggregation dynamics for a series of regioregular poly(3-hexylthiophene)s with different degrees of polymerization can be condensed into a general growth model, with a clear separation between aggregation and planarization/stacking of the polymers.