Conjugated core-shell bottlebrush polymers that exhibit crystallization-driven self-assembly

Bottlebrush polymers are complex architectures with densely grafted polymer side chains along polymeric backbones. The dense and conformationally extended chains in bottlebrush polymers give rise to unique properties, including low chain entanglement, low critical aggregation concentrations, and elastomeric properties in the bulk phase. Conjugated polymers have garnered attention as lightweight, processible, and flexible semi-conducting materials. They are promising candidates in electronic devices and sensors, but their optoelectronic properties depend on adequate polymer ordering, π-π interactions, and crystallization. Crystallization-driven self-assembly of conjugated polymers has become a prominent method to optimize properties including band energies, redox potentials, and exciton diffusion and transport. Much progress has been made in controlled block copolymer self-assembly, but despite their promising properties, reports of conjugated bottlebrushes have been limited, and their self-assembly is relatively unexplored. For the first time, we report the synthesis of conjugated core-shell bottlebrush polymers. These materials contain poly(3-hexylthiophene) (P3HT) and poly(ethylene glycol) (PEG) in either core or shell position. We demonstrate that the use of P3HT as a crystallizable conjugated polymer and PEG as a colloidally stabilizing and disaggregating block facilitates their self-assembly into a number of unique crystalline morphologies with longer conjugation lengths and lower exciton bandwidths relative to analogous diblock copolymers. These include intramolecularly self-assembled segregated bottlebrush polymers, short nanofibers formed by end-on-end stacking of bottlebrush molecules, extremely long >20 μm nanofibers formed exclusively by end-on-end stacking, and >15 μm nanoribbons formed from both end-on-end and side-by-side stacking of bottlebrush polymers.

Efficient Production of Epoxy-Norbornane from Norbornene by an Engineered P450 Peroxygenase

Epoxy-norbornane (EPO-NBE) is a crucial building block for the synthesis of various biologically active heterocyclic systems. To develop an efficient protocol for producing EPO-NBE using norbornene (NBE) as a substrate, cytochrome P450 enzyme from Pseudomonas putida (CYP238A1) was examined and its crystal structure (PDB code: 7X53) was resolved. Molecular mechanism analysis showed a high energy barrier related to iron-alkoxy radical complex formation. Therefore, a protein engineering strategy was developed and an optimal CYP238A1^NPV variant containing a local hydrophobic "fence" at the active site was obtained, which increased the H₂ O₂ -dependent epoxidation activity by 7.5-fold compared with that of CYP238A1^WT . Among the "fence", Glu255 participates in an efficient proton transfer system. Whole-cell transformation using CYP238A1^NPV achieved an EPO-NBE yield of 77.6 g ⋅ L^-1 in a 30-L reactor with 66.3 % conversion. These results demonstrate the potential of this system for industrial production of EPO-NBE and provides a new biocatalytic platform for epoxidation chemistry.

A grafting-from strategy for the synthesis of bottlebrush nanofibers from organic semiconductors

Bottlebrush polymers with optoelectronic function show promise for applications in photonic crystals, nanomedicine, and encoding of information. In particular, bottlebrush polymers formed from organic semiconductors give wire-like nanoparticles where band gaps, fluorescence, and energy transfer can be tuned. To date, such bottlebrush polymers have largely been prepared by grafting-through polymerization of organic semiconductor macromonomers, where pre-synthesized side chains are polymerized along a bottlebrush backbone. While this approach provides high side-chain grafting densities, the length of bottlebrush polymers that is possible to obtain is limited by steric crowding at the propagating chain end. Here, we describe methods for preparing ultralong bottlebrush nanofibers from organic semiconductors, with backbone lengths approaching 800 repeating units and molecular weights in excess of 4 MDa. By combining reversible addition fragmentation chain transfer and Cu(0) reversible deactivation radical polymerization, a “grafting-from” protocol is described where monomers can be grown from a pre-synthesized backbone. Bottlebrush polymers were prepared from organic semiconductors used as n-type, p-type, and host materials in multilayer organic devices. Finally, a two-component bottlebrush polymer exhibiting deep blue emission, two-photon fluorescence, and a quantum yield of unity is also prepared by this method.

From macromonomers to bottlebrush copolymers with sequence control: synthesis, properties, and applications

Bottlebrush polymers (BBPs) are a type of comb-like macromolecules with densely grafted polymeric sidechains attached to the polymer backbones, and many intriguing properties and applications have been demonstrated due to...

Synthesis and Self-Assembly of Conjugated Block Copolymers

In the past two decades, conjugated polymers (CPs) have drawn great attention due to their excellent conductivity and charge mobility, rendering them broad applications in organic electronics. Controlling over the morphologies and nanostructures of CPs is very important to improve the performance of CP-based devices, which is still a tremendously difficult task. Conjugated block copolymers (cBCPs), composed of different CP blocks or CP coupled with coiled polymeric blocks, not only maintain the advantages of high conductivity and mobility but also demonstrate features of morphological versatility and tunability. Due to the strong π-π interaction and crystallinity of the conjugated backbones, the self-assembly behaviors of cBCPs are very complicated and largely remain to be explored. In this tutorial review, we first summarize the general synthetic methods for different types of cBCPs. Then, recent studies on the self-assembly behaviors of cBCPs are discussed, with an emphasis on the structural factors that affect the morphologies of cBCPs both in bulk and thin film states. Finally, we briefly provide our outlook on the future research of the self-assembly of cBCPs.

Amphiphilic multicomponent molecular brushes

Multicomponent molecular brushes containing amphiphilic polymer moieties are promising objects of research of macromolecular chemistry. The development of stimulus-responsive systems sensitive to changes in environmental parameters, based on the molecular brushes, opens up new possibilities for their applications in medicine, biochemistry and microelectronics. The review presents the current understanding of the structures of main types of amphiphilic multicomponent brushes, depending on the chemical nature and type of coupling of the backbone and side chains. The approaches to the controlled synthesis of multicomponent molecular brushes of different architecture are analyzed. Self-assembly processes of multicomponent molecular brushes in selective solvents are considered.

The bibliography includes 259 references.

Grubbs' and Schrock's Catalysts, Ring Opening Metathesis Polymerization and Molecular Brushes-Synthesis, Characterization, Properties and Applications

In this review, molecular brushes and other macromolecular architectures bearing a bottlebrush segment where the main chain is synthesized by ring opening metathesis polymerization (ROMP) mediated by Mo or Ru metal complexes are considered. A brief review of metathesis and ROMP is presented in order to understand the problems and the solutions provided through the years. The synthetic strategies towards bottlebrush copolymers are demonstrated and each one discussed separately. The initiators/catalysts for the synthesis of the backbone with ROMP are discussed. Syntheses of molecular brushes are presented. The most interesting properties of the bottlebrushes are detailed. Finally, the applications studied by different groups are presented.

Linear and Multi-Photon Fluorescence of Thiophene Based Copolymer with Electron-Accepting Side Chains

A novel copolymer poly(thiophene-2,5-diyl-2,5-di-n-octyloxycarbonyl-1,4-phenylene), denoted as P33, is introduced as potential material for photovoltaics, polymer light-emitting diodes, and/or organic transistors. P33 dissolved in chloroform is investigated by steady-state absorption, linear/non-linear fluorescence spectroscopies and time-resolved fluorescence spectroscopy. Molar extinction coefficient, fluorescence quantum yield, and singlet fluorescence lifetime of P33 are determined to be 18,315 M^-1 cm^-1, 0.4, and 810 ps, respectively. The P33 fluorescence fast components of decay times are 1.2 ps, 2.0 ps, and 0.5 ps for increasing wavelengths of 480 nm, 500 nm, and 520 nm, respectively. The fast component is attributed to a transport of nearly instantaneously formed excitons to localized states known as downhill energy transfer. Additionally multi-photon excited fluorescence is observed for pumping with wavelengths of 800 nm and 1200 nm. Two-photon absorption cross-section is determined to be 6.9 GM. These spectroscopic studies provide basic fluorescence characteristics of the novel thiophene copolymer P33.