Protonation-induced transient amphiphilicity drives the self-assembly of conjugated polymers into spheres and other aggregates

Robust, luminescent, spherical, and ribbonlike aggregates were self-assembled from nonamphiphilic pi-conjugated polymers, poly(4-alkylquinoline)s, in toluene/trifluoroacetic acid solution. The spherical and ribbonlike aggregates in solution or in the solid state exhibited yellow fluorescence that was characterized by microscopy and spectroscopy. The 1-10-mum-diameter spherical aggregates of poly(4-hexylquinoline) and poly(4-tridecylquinoline) were shown by laser scanning confocal microscopy to be solid spheres. We propose that the novel self-assembly is driven by the amphiphilicity of transient poly(4-alkylquinolinium) activated by protonation of poly(4-alkylquinoline). Beyond the self-assembly of electronic and photonic polymer microstructures, the concept of transient amphiphilicity may find other applications in supramolecular chemistry and biomimetic systems.