Synthesis and Photoresponse of Helically Folded Poly(phenyleneethynylene)s Bearing Azobenzene Moieties in the Main Chains

Azobenzene-Based Conjugated Polymers: Synthesis, Properties, and Biological Applications

Conjugated polymers (CPs) have been developed quickly as an emerging functional material with applications in optical and electronic devices, owing to their highly electron-delocalized backbones and versatile side groups for facile processibility, high mechanical strength, and environmental stability. CPs exhibit multistimuli responsive behavior and fluorescence quenching properties by incorporating azobenzene functionality into their molecular structures. Over the past few decades, significant progress has been made in developing functional azobenzene-based conjugated polymers (azo-CPs), utilizing diverse molecular design strategies and synthetic pathways. This article comprehensively reviews the rapidly evolving research field of azo-CPs, focusing on the structural characteristics and synthesis methods of general azo-CPs, as well as the applications of charged azo-CPs, specifically azobenzene-based conjugated polyelectrolytes (azo-CPEs). Based on their molecular structures, azo-CPs can be broadly categorized into three primary types: linear CPs with azobenzene incorporated into the side chain, linear CPs with azobenzene integrated into the main chain, and branched CPs containing azobenzene moieties. These systems are promising for biomedical applications in biosensing, bioimaging, targeted protein degradation, and cellular apoptosis.

Unraveling Dynamic Helicity Inversion and Chirality Transfer through the Synthesis of Discrete Azobenzene Oligomers by an Iterative Exponential Growth Strategy

Unraveling the chirality transfer mechanism of polymer assemblies and controlling their handedness is beneficial for exploring the origin of hierarchical chirality and developing smart materials with desired chiroptical activities. However, polydisperse polymers often lead to an ambiguous or statistical evaluation of the structure-property relationship, and it remains unclear how the iterative number of repeating units function in the helicity inversion of polymer assemblies. Herein, we report the macroscopic helicity and dynamic manipulation of the chiroptical activity of supramolecular assemblies from discrete azobenzene-containing oligomers (azooligomers), together with the helicity inversion and morphological transition achieved solely by changing the iterative chain lengths. The corresponding assemblies also differ from their polydisperse counterparts in terms of thermodynamic properties, chiroptical activities, and morphological control.

Facile Synthesis of Light-Switchable Polymers with Diazocine Units in the Main Chain

Unlike azobenzene, the photoisomerization behavior of its ethylene-bridged derivative, diazocine, has hardly been explored in synthetic polymers. In this communication, linear photoresponsive poly(thioether)s containing diazocine moieties in the polymer backbone with different spacer lengths are reported. They were synthesized in thiol-ene polyadditions between a diazocine diacrylate and 1,6-hexanedithiol. The diazocine units could be reversibly photoswitched between the (Z)- and (E)-configurations with light at 405 nm and 525 nm, respectively. Based on the chemical structure of the diazocine diacrylates, the resulting polymer chains differed in their thermal relaxation kinetics and molecular weights (7.4 vs. 43 kDa) but maintained a clearly visible photoswitchability in the solid state. Gel permeation chromatography (GPC) measurements indicated a hydrodynamic size expansion of the individual polymer coils as a result of the Z→E pincer-like diazocine switching motion on a molecular scale. Our work establishes diazocine as an elongating actuator that can be used in macromolecular systems and smart materials.

Reversible Controlling the Supramolecular Chirality of Side Chain Azobenzene Polymers: chiral Induction and Modulation

Chirality represents a fundamental structure in nature, the induction and reversible modulation of supramolecular chirality with feasible techniques is of great value in the design of new chiroptical smart materials. Herein, two kinds of azobenzene side-chain polymers (without spacer: Azo-PMA0; with 6 spacers: Azo-PMA6) were synthesized, the length of spacer and azobenzene chromophores play a vital role in chirality transfer and modulation. The supramolecular chiral arrangement of Azo-PMA0 (amorphous phase) can be completely controlled and reversibly modulated over multiple cycles by 450 nm circularly polarized light (CPL) driven by the supramolecular interaction between azo groups of polymer chains, with an absorption dissymmetry factor (g) value of 0.0019. The chiroptical properties of Azo-PMA6 (liquid crystal state) can also be reversibly modulated by UV light and thermal annealing treatment during trans-cis isomerization of azo chromophore, with the g-value changes from 0-0.038. The successful construction of reversible chiral induction and modulation based on side chain azobenzene polymers may pave the way for designing photo-switchable functional materials. This article is protected by copyright. All rights reserved.

Intramolecular chalcogen bonding to tune molecular conformation of helical building block for supramolecular helix

We propose to employ intramolecular chalcogen bonding to make the helical building block take its otherwise unfavorable cis-conformation. 2,5-Thiophenediamide motif was taken to bridge two β-turn structures to lead to...

Conformational Switch of Arylopeptide: Helix-Helix Transition Based on Side Chain Solvation

Controlling the structural transition between well-defined architectures found in living system is essential in polymer chemistry as well as material science. Herein, the reversible conformational switch of a non-natural polypeptide with an aromatic ring (2,6-naphthalene spacer) on its peptide backbone, referred to as an arylopeptide, between two distinct well-defined helical structures (extended 3₁ -helix and contracted 4₁ -helix) using side chain solvation is demonstrated. The folding selectivity of the arylopeptide and found that the affinity between the solvent and side chains is an essential factor for determining the global structure is investigated. A thermoresponsive arylopeptide bearing oligoether groups (─(CH₂ CH₂ O)₉ CH₃ )) on the side chain is designed, which exhibited unique lower critical solution temperature behavior and converted from the 3₁ to the 4₁ -helix depending on the temperature. Furthermore, the solvent affinity of the entire polymer by combining substituents (─(CH₂ CH₂ O)₃ CH₃ and ─C₁₂ H₂₅ ) with different properties on the side chains to achieve a spring-like expansion-contraction system that allows interconversion between 3₁ - and 4₁ -helices is adjusted.

Aggregation-induced chiroptical generation and photoinduced switching of achiral azobenzene-alt-fluorene copolymer endowed with left- and right-handed helical polysilanes

The left and right helicities of azobenzene (Azo)-containing main-chain polymer (PF8Azo) were successfully controlled with an enantiomeric pair of rigid rod-like helical polysilanes carrying (S)- and (R)-2-methylbutyl groups (PSi-S and PSi-R, respectively) as their hetero-aggregates in a mixture of chloroform and methanol solvents and in the solid state. Optimizing the good and poor cosolvents and their volume fractions showed that the molar ratio of PF8Azo to PSi-S/-R and the molecular weight of PF8Azo were crucial to boost the CD amplitudes of PF8Azo/PSi-S and PF8Azo/PSi-R hetero-aggregates. The photoresponsive trans-cis transformation caused noticeable changes in the sign and magnitude of the chiroptical behavior due to the hetero-aggregates. Moreover, the optically active PF8Azo homo-aggregates were produced by complete photoscissoring reactions at 313 nm, which could be assigned to the Siσ-Siσ* transitions of PSi-S and PSi-R.

Establishment of a molecular design to obtain visible-light-activated azoxy polymer actuators

Visible-light-activated main-chain and hyperbranched azoxy polymers were prepared directly from bis-/trinitro-functionalized monomers via photochemical reduction.

Synthesis and characterization of visible-light-activated Azo hyperbranched polymers

All visible-light-activated Azo polymer photoswitches were efficiently synthesized via combination of the AuNP-catalyzed photocatalytic method and the A₃ monomer strategy.

Remote control over folding by light

Integrating photoswitchable unit into helical macromolecules allows their conformations to be externally controlled by light and therefore provides a versatile strategy to design photoresponsive materials.

Synthesis of platinum-containing poly(phenyleneethynylene)s having various chromophores: aggregation and optical properties

Various platinum-containing phenylene–ethynylene–arylene polymers were synthesized, and the relationships between the optical properties and aggregation behaviour were examined.

Azobenzenes and catalysis

Azobenzene is the most extensively used class of chromophore in a large variety of applications.

Photocontrollable induction of supramolecular chirality in achiral side chain Azo-containing polymers through preferential chiral solvation

The preferred supramolecular chirality in aggregates of achiral azobenzene-containing polymers by limonene as a chiral transducer is achieved for the first time.

Preferential chiral solvation induced supramolecular chirality in optically inactive star Azo polymers: photocontrollability, chiral amplification and topological effects

The chiral amplification phenomena were observed for the first time in 4- and 6-armed Azo star side-chain polymer systems, but absent in linear and 3-armed counterparts.