Harmonic light scattering study reveals structured clusters upon the supramolecular aggregation of regioregular poly(3-alkylthiophene)

Solubilized poly(3-alkylthiophene)s are known to self-assemble into well-ordered supramolecular aggregates upon lowering the solvent quality. This supramolecular organization largely determines the optical and electronic properties of these polymers. However, despite numerous studies the exact mechanism and kinetics of the aggregation process and the role of external stimuli are still poorly understood. Classical characterization techniques such as electronic spectroscopy, dynamic light scattering, and diffraction-based techniques have not been able to provide a full understanding. Here we use second-harmonic scattering (SHS) and third-harmonic scattering (THS) techniques to investigate this supramolecular aggregation mechanism. Our results indicate that the actual supramolecular aggregation is preceded by the formation of structured polymer-solvent clusters consistent with a nonclassical crystallization pathway.