Herein, we report a high-yield click synthesis and self-assembly of conjugated amphiphilic block copolymers of polythiophene (PHT) and polyethylene glycol (PEG) and their superstructures. A series of different length PHT(m)-b-PEG(n) with well-defined relative block lengths was synthesized by a click-coupling reaction and self-assembled into uniform and stably suspended nanofibers in selective solvents. The length of nanofibers was controllable by varying the relative block lengths while keeping other dimensions and optical properties unaffected for a broad range of f(PHT) (0.41 to 0.82), which indicates that the packing of PHT dominates the self-assembly of PHT(m)-b-PEG(n). Furthermore, superstructures of bundled and branched nanofibers were fabricated through the self-assembly of PHT(m)-b-PEG(n) and preformed PHT nanofibers. The shape, length, and density of the hierarchical assembly structures can be controlled by varying the solvent quality, polymer lengths, and block copolymer/homopolymer ratio. This work demonstrates that complex superstructures of organic semiconductors can be fabricated through the bottom-up approach using preformed nanofibers as building blocks.

Nanoparticles can form unique cavity-like structures in core-shell type assemblies of block copolymers through the cooperative self-assembly of nanoparticles and block copolymers. We show that the self-assembly behavior is general for common as-synthesized alkyl-terminated nanoparticles for a range of nanoparticle sizes. We examined various self-assembly conditions such as solvent compositions, nanoparticle coordinating ligands, volume fraction of nanoparticles, and nanoparticle sizes in order to elucidate the mechanism of the radial assembly formation. These experiments along with strong segregation theory calculations indicated that both the enthalpic interaction and the polymer stretching energy are important factors in the coassembly formation. The slightly unfavorable interaction between the hydrophobic segment of polymers and alkyl-terminated nanoparticles causes the accumulation of nanoparticles at the interface between the polymer core and the shell, forming the unique cavity-like structure. The coassemblies were stabilized for a limited range of nanoparticle volume fractions within which the inclusion of nanoparticle layers reduces the polymer stretching. The volume fraction range yielding the well-defined radial coassembly structure was mapped out with varying nanoparticle sizes. The experimental and theoretical phase map provides the guideline for the coassembly formation of as-synthesized alkyl-terminated nanoparticles and amphiphilic block copolymers.

The colloidal self-assembly of a new conjugated diblock copolymer of a polythiophene derivative, poly [3-(2,5,8,11tetraoxatridecanyl)thiophene]-block-poly(ethylene glycol) (PTOTTb-PEG), led to various well-defined assembly structures such as vesicles, sheets, and nanoribbons. A unique and technologically relevant nanoribbon structure with a dimension reaching tens of micrometers was formed in water when polar protic solvents were used as initial cosolvents. Self-assembly of PTOTT-b-PEG in various solvent compositions and polymer concentrations indicated that the hydrogen bonding between the diblock copolymer and the self-assembly medium plays an important role in determining the self-assembly structure and that the final assembly structure should be the result of a delicate interplay between hydrogen bonding and π−π interactions. This study demonstrates that the addition of hydrogen bonding capability and amphiphilicity in the self-assembly of conjugated polymers can lead to many interesting well-defined assembly structures that are not typically found in conjugated polymers.

We describe the synthesis and self-assembly of amphiphilic semiconducting polymers composed of a polythiophene derivative (i.e., poly [3-(2,5,8,11-tetraoxatridecanyl)thiophene] (PTOTT)) and an oligonucleotide, DNA-b-PTOTT. These new bioconjugated polymers combine the excellent optoelectronic properties of semiconducting polymers and the programmable molecular recognition properties of DNA. Because of the unique combination of rigid polythiophene and highly negatively charged DNA, they self-assemble into size-controllable vesicles in water. DNA-modified one-dimensional polythiophene nanoribbons were formed by simultaneous assembly of DNA-b-PTOTT with PEG-b-PTOTT, demonstrating that various types of DNA-modified functional nanostructures can be formed by the mixed assembly. This approach offers a new pathway to couple various types of soft optoelectronic nanostructures with DNA's molecular recognition properties.

ACKNOWLEDGMENT S.-J.P. is thankful for financial support from a MRSEC seed award (DMR 05-20020), NSF career award, and ARO young investigator award. B.B.W. acknowledges the support from NSF-CHE: 0809395. N.C. thanks the EPSRC for an Overseas Travel Grant (EP/E050794/1).