Spontaneous Formation of Polymeric Nanoribbons in Water Driven by π-π Interactions

A simple method was developed to produce polymeric nanoribbons and other nanostructures in water. This approach incorporates a perylene diimide (PDI) functionalized by triethylene glycol (TEG) as a hydrophobic supramolecular structure directing unit (SSDU) 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): nanoribbons and nanocylinders for DP_n=14 and 22, and spheres for DP_n>50 as determined by cryo-TEM and SAXS analyses. UV/Vis absorption spectroscopy was used to monitor the evolution of the PDI absorption signal upon dissolution. In solid form, all polymers show a H-aggregate absorption signature, but upon dissolution in water, the shortest DP_n forming nanoribbons evolved to show HJ-aggregate absorption signals. Over time, the J-aggregate band increased in intensity, while cryo-TEM monitoring evidenced an increase in the nanoribbon's width. Heating the nanoribbons above 60 °C, triggered a morphological transition from nanoribbons to nanocylinders, due to the disappearance of J-aggregates, while H-aggregates were maintained. The study shows that the TEG-PDI is a powerful SSDU to promote 2D or 1D self-assembly of polymers depending on DP_n through simple dissolution in water.