Efficient and Controlled Seeded Growth of Poly(3-hexylthiophene) Block Copolymer Nanofibers through Suppression of Homogeneous Nucleation

Conducting Electrospun Poly(3-hexylthiophene-2,5-diyl) Nanofibers: New Strategies for Effective Chemical Doping and its Assessment Using Infrared Spectroscopy

Vibrational spectroscopy allows the investigation of structural properties of pristine and doped poly(3-hexylthiophene-2,5-diyl) (P3HT) in highly anisotropic materials, such as electrospun micro- and nanofibers. Here, we compare several approaches for doping P3HT fibers. We have selected two different electron acceptor molecules as dopants, namely iodine and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). In the case of iodine, we have explored the doping of the fibers according to several different procedures, i.e., by sequential doping both in vapors and in solution, and with a novel promising one-step method, which exploits the mixing of the dopant to the electrospinning feed solution. Polarized infrared (IR) spectroscopy experiments prove the orientation of P3HT chains, with the polymer backbone mainly running parallel to the fiber axis. After doping, P3HT fibers show very strong and polarized doping-induced IR active vibrations (IRAVs), which are the spectroscopic signature of the structure relaxation induced by the charged defects (polarons), thus providing an unambiguous proof of the effective doping. Raman spectroscopy complements the IR evidence: The Raman spectrum shows a clearly recognizable shift of the main band, the so-called effective conjugation coordinate band, in the doped samples. A simple protocol, which quantifies the evolution of the IRAV bands with time, allows monitoring of the doping stability over time and confirms that F4TCNQ is by far superior to iodine.

Highly Efficient Preparation of Length and Width-Controllable Donor-Acceptor Nanoribbons via Polymerization-Induced Crystallization-Driven Self-Assembly of Fully Conjugated Block Copolymers

Despite the high potential of one-dimensional (1D) donor-acceptor (D-A) coaxial nanostructures in bulk-heterojunction solar cell applications, the preparation of such 1D nanostructures using π-conjugated polymers has remained elusive. Herein, we demonstrate the first example of D-A semiconducting nanoribbons based on fully conjugated block copolymers (BCPs) prepared in a highly efficient procedure with controllable width and length via living crystallization-driven self-assembly (CDSA). Initially, Suzuki-Miyaura catalyst-transfer polymerization was employed to successfully synthesize BCPs containing two types of acceptor shells as the first block, followed by a donor poly(3-propylthiophene) core as the second block. The limited solubility and high crystallinity of the core induced a polymerization-induced crystallization-driven self-assembly (PI-CDSA) of the BCPs into nanoribbons during polymerization, providing a tunable width (7.6-39.6 nm) depending on the length of the polymer backbone. Surprisingly, purifying as-synthesized BCPs via simple precipitation directly yielded short and uniform seed structures, greatly shortening the overall protocol by eliminating the time-consuming process of initial aging and breaking down to the seed required for the conventional CDSA. With this new highly efficient method, we achieved length control over a broad range from 169 to 2210 nm, with high precision (Lw/Ln < 1.20). Furthermore, combining self-seeding and seeded growth from two different D-A-type BCPs enabled continuous living epitaxial growth from each end of the nanoribbons, resulting in B-A-B triblock D-A semiconducting comicelles with controlled length.

Surface-Initiated Living Self-Assembly of Polythiophene-Based Conjugated Block Copolymer into Erect Micellar Brushes

Nanostructured conjugated polymers are of widespread interest due to their broad applications in organic optoelectronic devices, biomedical sensors and other fields. However, the alignment of conjugated nanostructures perpendicular to a surface remains a critical challenge. Herein, we report a facile method to directly self-assemble a poly(3-(2-ethylhexyl)thiophene), P3EHT-based block copolymer into densely aligned micellar brushes through surface-initiated living crystallization-driven self-assembly. The presence of an ethyl pendant on the side group intrinsically moderates the crystallization rate of the polythiophene main chains, and hence favors the controlled living growth of long conjugated fibers and the subsequent fabrication of conjugated micellar brushes. The corona of the micellar brush can be further decorated with platinum nanoparticles, which enables the formation of erect nanoarrays with heights up to 2700 nm in the dried state. This also renders the micellar brush catalytically active toward hydrogen evolution reaction, which shows a low overpotential of 27 mV at 10 mA cm-2 . Notably, the P3EHT-based micellar brush can simultaneously grow with polyferrocenyldimethylsilane, PFS-based micellar brush on the same surface without any significant interference between the two systems. Thus, these two micellar brushes can be patterned through site-selective immobilization of two types of seeds followed by independent living self-assembly.

Length-Dependent Cellular Internalization of Nanobody-Functionalized Poly(2-oxazoline) Nanorods

The ability to target specific tissues and to be internalized by cells is critical for successful nanoparticle-based targeted drug delivery. Here, we combined "stealthy" rod-shaped poly(2-oxazoline) (POx) nanoparticles of different lengths with a cancer marker targeting nanobody and a fluorescent cell internalization sensor via a heat-induced living crystallization-driven self-assembly (CDSA) strategy. A significant increase in association and uptake driven by nanobody-receptor interactions was observed alongside nanorod-length-dependent kinetics. Importantly, the incorporation of the internalization sensor allowed for quantitative differentiation between cell surface association and internalization of the targeted nanorods, revealing unprecedented length-dependent cellular interactions of CDSA nanorods. This study highlights the modularity and versatility of the heat-induced CDSA process and further demonstrates the potential of POx nanorods as a modular nanomedicine platform.

Dopant-Stabilized Assembly of Poly(3-hexylthiophene)

Polymer self-assembly is a powerful approach for forming nanostructures for solution-phase applications. However, polymer semiconductor assembly has primarily been driven by solvent interactions. Here, we report poly(3-hexythiophene) homopolymer assembly driven and stabilized by oxidative doping with iron (III) p-toluenesulfonate in benzonitrile. By this improved method, dopant mol % and addition temperature determine the size and morphology of oxidized polymer nanostructures. The dopant counterion provides colloidal stability in a process of dopant-stabilized assembly (DSA). Each variable governing polymer assembly is systematically varied, revealing general principles of oxidized nanostructure assembly and allowing the polymer planarity, optical absorption, and doping level to be modulated. Oxidized nanostructure heights, lengths, and widths are shown to depend on these properties, which we hypothesize is due to competing nanostructure formation and oxidation mechanisms that are governed by the polymer conformation upon doping. Finally, we demonstrate that the nanoparticle oxidative doping level can be tuned post-formation through sequential dopant addition. By revealing the fundamental processes underlying DSA, this work provides a powerful toolkit to control the assembly and optoelectronic properties of oxidatively doped nanostructures in solution.

Group 16 conjugated polymers based on furan, thiophene, selenophene, and tellurophene

Five-membered aromatic rings containing Group 16 elements (O, S, Se, and Te), also referred as chalcogenophenes, are ubiquitous building blocks for π-conjugated polymers (CPs). Among these, polythiophenes have been established as a model system to study the interplay between molecular structure, solid-state organization, and electronic performance. The judicious substitution of alternative heteroatoms into polythiophenes is a promising strategy for tuning their properties and improving the performance of derived organic electronic devices, thus leading to the recent abundance of CPs containing furan, selenophene, and tellurophene. In this review, we first discuss the current status of Kumada, Negishi, Murahashi, Suzuki-Miyaura, and direct arylation polymerizations, representing the best routes to access well-defined chalcogenophene-containing homopolymers and copolymers. The self-assembly, optical, solid-state, and electronic properties of these polymers and their influence on device performance are then summarized. In addition, we highlight post-polymerization modifications as effective methods to transform polychalcogenophene backbones or side chains in ways that are unobtainable by direct polymerization. Finally, the major challenges and future outlook in this field are presented.