Uniform Rectangular Conjugated Polymer Platelet Micelles via One-Step Crystallization-Driven Nucleation-Growth

Semiconducting organic nanocrystals derived from the self-assembly of conjugated polymers hold great promise for optoelectronic applications. However, fabrication of these semiconductors with high uniformity and extended dimensions remains a major challenge due to tedious multistep procedures for size control and the formidable task of attaining crystal growth oriented perpendicularly to the π-π stacking direction. Here, we present a straightforward strategy for the preparation of uniform rectangular platelet micelles with tunable size through a single-step heating-cooling-aging protocol from conjugated poly(di-n-hexylfluorene) (PDHF) block copolymers (BCPs). The nucleation and growth stages are dramatically separated during the cooling process, wherein BCPs with longer PDHF blocks spontaneously serve as in situ nuclei and induce controllable epitaxial growth, yielding uniform two-dimensional (2D) morphologies. The crystalline core structure is long-range ordered, synchronously constructed by pitched π-π stacking in the length-growth direction and solvophobic alkyl stacking in the width-growth direction. The platelet dimensions spanning ∼30,000-800,000 nm² can be controlled by adjusting the mixed solvent ratio. Furthermore, the universality of this one-step strategy for size-controllable platelets is affirmed by BCPs with varying corona-core block ratios (0.20-0.86) and different corona-forming chains (e.g., quaternized polythiophene (QPT) and polyfluorene (QPF)). Interestingly, complex concentric segmented structures are accessible through the one-pot self-assembly of two PDHF BCPs, whose growth rate and sequence are manipulated by differences in PDHF block lengths (17 versus 14) and block ratios (0.12 versus 0.71). This enables the customization of a facile energy funneling pathway within the integrated structures from the peripheral, crystalline PDHF core to the central, lower-energy QPT corona.