We present direct method to produce polymeric nanoribbons and other nanostructures in water. This approach incorporates perylene diimide (PDI) as a hydrophobic supramolecular structure directing unit into the core of hydrophilic poly(N,N-dimethylacrylamide) (PDMAc) chains using RAFT polymerization. All PDI-functional polymers dissolved spontaneously in water, forming different nanostructures depending on the degree of polymerization (DP_n): ribbons and fibers for DP_n = 14 and 22, and spherical nano-objects for DP_n > 50. Cryo-TEM and SAXS analyses confirmed the nanoribbon and nanofiber formations.

UV-visible absorption spectroscopy was used to monitor the evolution of the PDI absorption signal upon dissolution. In powder form, the polymers showed absorption signatures corresponding to H-aggregates, but upon dissolution, the shortest DP_n (14) forming nanoribbons evolved to show also J-aggregate absorption bands. Over time, we could also confirm by an increase in the J-aggregate band the growth of the nanoribbons. A quasi-reversible transition between nanoribbons and nanofibers was also observed with increasing temperature, above 60°C. This study demonstrates that different π-conjugated nanostructures can be easily obtained in a controlled manner through direct dissolution in water.

The controlled formation of well-defined nanoribbons and nanofibers with π-conjugated cores could significantly improve charge transport in organic semiconductors. Moreover, the water-soluble nature of these polymeric nanostructures presents a significant advantage for device fabrication.

Lydia SOSA VARGAS

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