Fiber-Like Micelles from the Crystallization-Driven Self-Assembly of Poly(3-heptylselenophene)-block-Polystyrene

The crystallization-driven self-assembly (CDSA) of crystalline-coil polyselenophene diblock copolymers represents a facile approach to nanofibers with distinct optoelectronic properties relative to those of their polythiophene analogs. The synthesis of an asymmetric diblock copolymer with a crystallizable, -conjugated poly(3-heptylselenophene) (P3C7Se) block and an amorphous polystyrene (PS) coblock is described. CDSA was performed in solvents selective for the PS block. Based on transmission electron microscopy (TEM) analysis, P3C7Se(18)-b-PS125 formed very long (up to 5 m), highly aggregated nanofibers in n-butyl acetate (nBuOAc) whereas shorter (ca. 500 nm) micelles of low polydispersity were obtained in cyclohexane. The micelle core widths in both solvents determined from TEM analysis (approximate to 8 nm) were commensurate with fully-extended P3C7Se(18) chains (estimated length = 7.1 nm). Atomic force microscopy (AFM) analysis provided characterization of the micelle cross-section including the PS corona (overall micelle width approximate to 60 nm). The crystallinity of the micelle cores was probed by UV-vis and photoluminescence (PL) spectroscopy and wide-angle X-ray scattering (WAXS).