Entropy-Driven Heterocomplexation of Conjugated Polymers in Highly Diluted Solutions

Examples
of complexes formed by the association of two dissimilar
polymers are scarce. We unravel in this report a rare phenomenon of
complexation of two conjugated polymers in highly diluted solutions.
Spectroscopy characterization of titrated solutions combined with
molecular dynamics and time-dependent density functional theory reveal
the presence of strong supramolecular interactions giving rise to
the formation of conjugated heterocomplexes of the distinctive charge
transfer electronic character. Temperature-dependent studies provide
association constants in the 104 to 105 M–1 range and negative van’t Hoff slopes characteristic
of entropy-driven association. We explain the entropy gain as the
result of solvent molecule release and their subsequent redistribution
upon polymer association. Our findings have implications in the field
of organic photovoltaics, where the mixing/segregation of polymers
of different electronic characters is key to performance.