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Azobenzene and Applications: From Catalysis to Biology

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 20321

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Dr. Estelle Léonard

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Guest Editor

Integrated Transformations of Renewable Materials, UTC/ESCOM, F-60200 Compiegne, France
Interests: azobenzenes; photochromic molecules; catalysis; organic reactions; chemobiology
Special Issues, Collections and Topics in MDPI journals

Dr. Muriel Billamboz

E-Mail Website
Guest Editor

Health & Environment Department, YNCREA Hauts-de-France, F-59046 Lille, France
Interests: medicinal chemistry; drug discovery; catalysis; photochromic molecules
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Amongst the class of photochromic molecules and the large variety of applications in photoregulation, azobenzenes are the most intensively used and produced, with more than 60% of the total production in the organic dyes domain, as an example. Diazo can switch reversibly from the trans-isomer to the cis-isomer by torsion or inversion, under light or heat, and this is—more than their color panel—their main specificity in their various applications.

This Special Issue will bring together researchers from different disciplines with the aim of having recent advances and synopses of the azobenzenes field, from their synthesis to their applications in catalysis or biology. A particular interest would be paid to azobenzene synthesis from natural resources, the use of azobenzenic compounds as ligands or microreactors in catalytic processes, and to applications of azobenzenes for health purposes such as innovative antimicrobials or photopharmacological tools.

Dr. Muriel Billamboz
Dr. Estelle Léonard
Guest Editors

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Keywords

Azobenzenes
Azo-ligands
Azobenzene as reactant
Azobenzene as product
Azobenzene-based organometallic catalysis
Antimicrobial azobenzenes
Photopharmacology

Published Papers (7 papers)

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Research

25 pages, 6467 KiB

Open AccessArticle

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars

by Markus Koch, Marina Saphiannikova and Olga Guskova

Molecules 2021, 26(24), 7674; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26247674 - 18 Dec 2021

Cited by 6 | Viewed by 2558

Abstract

This computational study investigates the influence of light on supramolecular aggregates of three-arm azobenzene stars. Every star contains three azobenzene (azo) moieties, each able to undergo reversible photoisomerization. In solution, the azo stars build column-shaped supramolecular aggregates. Previous experimental works report severe morphological changes of these aggregates under UV–Vis light. However, the underlying molecular mechanisms are still debated. Here we aim to elucidate how light affects the structure and stability of the columnar stacks on the molecular scale. The system is investigated using fully atomistic molecular dynamics (MD) simulations. To implement the effects of light, we first developed a stochastic model of the cyclic photoisomerization of azobenzene. This model reproduces the collective photoisomerization kinetics of the azo stars in good agreement with theory and previous experiments. We then apply light of various intensities and wavelengths on an equilibrated columnar stack of azo stars in water. The simulations indicate that the aggregate does not break into separate fragments upon light irradiation. Instead, the stack develops defects in the form of molecular shifts and reorientations and, as a result, it eventually loses its columnar shape. The mechanism and driving forces behind this order–disorder structural transition are clarified based on the simulations. In the end, we provide a new interpretation of the experimentally observed morphological changes. Full article

(This article belongs to the Special Issue Azobenzene and Applications: From Catalysis to Biology)

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25 pages, 6342 KiB

Open AccessArticle

Columnar Aggregates of Azobenzene Stars: Exploring Intermolecular Interactions, Structure, and Stability in Atomistic Simulations

by Markus Koch, Marina Saphiannikova and Olga Guskova

Molecules 2021, 26(24), 7598; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26247598 - 15 Dec 2021

Cited by 2 | Viewed by 2448

Abstract

We present a simulation study of supramolecular aggregates formed by three-arm azobenzene (Azo) stars with a benzene-1,3,5-tricarboxamide (BTA) core in water. Previous experimental works by other research groups demonstrate that such Azo stars assemble into needle-like structures with light-responsive properties. Disregarding the response to light, we intend to characterize the equilibrium state of this system on the molecular scale. In particular, we aim to develop a thorough understanding of the binding mechanism between the molecules and analyze the structural properties of columnar stacks of Azo stars. Our study employs fully atomistic molecular dynamics (MD) simulations to model pre-assembled aggregates with various sizes and arrangements in water. In our detailed approach, we decompose the binding energies of the aggregates into the contributions due to the different types of non-covalent interactions and the contributions of the functional groups in the Azo stars. Initially, we investigate the origin and strength of the non-covalent interactions within a stacked dimer. Based on these findings, three arrangements of longer columnar stacks are prepared and equilibrated. We confirm that the binding energies of the stacks are mainly composed of

π

–

π

interactions between the conjugated parts of the molecules and hydrogen bonds formed between the stacked BTA cores. Our study quantifies the strength of these interactions and shows that the

π

–

π

interactions, especially between the Azo moieties, dominate the binding energies. We clarify that hydrogen bonds, which are predominant in BTA stacks, have only secondary energetic contributions in stacks of Azo stars but remain necessary stabilizers. Both types of interactions,

π

–

π

stacking and H-bonds, are required to maintain the columnar arrangement of the aggregates. Full article

(This article belongs to the Special Issue Azobenzene and Applications: From Catalysis to Biology)

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11 pages, 2903 KiB

Open AccessArticle

Morphologically Diverse Micro- and Macrostructures Created via Solvent Evaporation-Induced Assembly of Fluorescent Spherical Particles in the Presence of Polyethylene Glycol Derivatives

by Mina Han, Ikue Abe, Kazunori Matsuura, Yukikazu Takeoka and Takahiro Seki

Molecules 2021, 26(14), 4294; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26144294 - 15 Jul 2021

Cited by 3 | Viewed by 2258

Abstract

The creation of fluorescent micro- and macrostructures with the desired morphologies and sizes is of considerable importance due to their intrinsic functions and performance. However, it is still challenging to modulate the morphology of fluorescent organic materials and to obtain insight into the factors governing the morphological evolution. We present a facile bottom-up approach to constructing diverse micro- and macrostructures by connecting fluorescent spherical particles (SPs), which are generated via the spherical assembly of photoisomerizable azobenzene-based propeller-shaped chromophores, only with the help of commercially available polyethylene glycol (PEG) derivatives. Without any extra additives, solvent evaporation created a slow morphological evolution of the SPs from short linear chains (with a length of a few micrometers) to larger, interconnected networks and sheet structures (ranging from tens to >100 µm) at the air–liquid interface. Their morphologies and sizes were significantly dependent on the fraction and length of the PEG. Our experimental results suggest that noncovalent interactions (such as hydrophobic forces and hydrogen bonding) between the amphiphilic PEG chains and the relatively hydrophobic SPs were weak in aqueous solutions, but play a crucial role in creating the morphologically diverse micro- and macrostructures. Moreover, short-term irradiation with visible light caused fast morphological crumpling and fluorescence switching of the obtained structures. Full article

(This article belongs to the Special Issue Azobenzene and Applications: From Catalysis to Biology)

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24 pages, 6252 KiB

Open AccessArticle

On the Low-Lying Electronically Excited States of Azobenzene Dimers: Transition Density Matrix Analysis

by Evgenii Titov

Molecules 2021, 26(14), 4245; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26144245 - 13 Jul 2021

Cited by 10 | Viewed by 2723 | Correction

Abstract

Azobenzene-containing molecules may associate with each other in systems such as self-assembled monolayers or micelles. The interaction between azobenzene units leads to a formation of exciton states in these molecular assemblies. Apart from local excitations of monomers, the electronic transitions to the exciton states may involve charge transfer excitations. Here, we perform quantum chemical calculations and apply transition density matrix analysis to quantify local and charge transfer contributions to the lowest electronic transitions in azobenzene dimers of various arrangements. We find that the transitions to the lowest exciton states of the considered dimers are dominated by local excitations, but charge transfer contributions become sizable for some of the lowest

π π^{*}

electronic transitions in stacked and slip-stacked dimers at short intermolecular distances. In addition, we assess different ways to partition the transition density matrix between fragments. In particular, we find that the inclusion of the atomic orbital overlap has a pronounced effect on quantifying charge transfer contributions if a large basis set is used. Full article

(This article belongs to the Special Issue Azobenzene and Applications: From Catalysis to Biology)

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13 pages, 1339 KiB

Open AccessArticle

Active Ester Functionalized Azobenzenes as Versatile Building Blocks

by Sven Schultzke, Melanie Walther and Anne Staubitz

Molecules 2021, 26(13), 3916; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26133916 - 26 Jun 2021

Cited by 4 | Viewed by 4585

Abstract

Azobenzenes are important molecular switches that can still be difficult to functionalize selectively. A high yielding Pd-catalyzed cross-coupling method under mild conditions for the introduction of NHS esters to azobenzenes and diazocines has been established. Yields were consistently high with very few exceptions. The NHS functionalized azobenzenes react with primary amines quantitatively. These amines are ubiquitous in biological systems and in material science. Full article

(This article belongs to the Special Issue Azobenzene and Applications: From Catalysis to Biology)

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14 pages, 4977 KiB

Open AccessArticle

Polarization Dependent Photoinduced Supramolecular Chirality in High-Performance Azo Materials

by Sekvan Bagatur, Marcel Schlesag and Thomas Fuhrmann-Lieker

Molecules 2021, 26(10), 2842; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26102842 - 11 May 2021

Cited by 3 | Viewed by 1946

Abstract

Here, we will show photo-induced supramolecular chirality in thin films of achiral amorphous polymers with azo groups in their side-chain. A matter of particular interest is the effect of various film thicknesses on azimuthal rotation and ellipticity of incident/transmitted polarized light. Furthermore, we investigated the temporal stability of inscribed chirality. By polarimetric measurements, we found out that the azimuthal rotation gets higher with layer thickness. In this scope, we were able to measure a very high azimuthal rotation of

Δ ψ / d = {112.5}^{\circ}

/μm. The inscribed chirality was stable for several days. Furthermore, we investigated the time-resolved behavior of incident and transmitted polarization ellipticities for various thicknesses. The time dependency may be explained by a two-step process: (1) fast trans-cis-isomerization resulting in photo-orientation and (2) slow photo-induced mass flow. Full article

(This article belongs to the Special Issue Azobenzene and Applications: From Catalysis to Biology)

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11 pages, 2188 KiB

Open AccessArticle

Metathesis Cyclopolymerization Triggered Self-Assembly of Azobenzene-Containing Nanostructure

by Wei Song, Jiamin Shen, Xiang Li, Jinhui Huang, Liang Ding and Jianhua Wu

Molecules 2020, 25(17), 3767; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25173767 - 19 Aug 2020

Cited by 4 | Viewed by 2278

Abstract

Azobenzene (AB) units were successfully introduced into poly(1,6-heptadiyne)s in order to ensure smooth synthesis of double- and single-stranded poly(1,6-heptadiyne)s (P1 and P2) and simultaneously realize the self-assembly by Grubbs-III catalyst-mediated metathesis cyclopolymerization (CP) of AB-functionalized bis(1,6-heptadiyne) and 1,6-heptadiyne monomers (M1 and M2). Monomers and polymers were characterized by ¹H NMR, mass spectroscopy, and GPC techniques. The double-stranded poly(1,6-heptadiyne)s exhibited a large scale of ordered ladder nanostructure. This result was attributed to the π−π attractions between end groups along the longitudinal axis of the polymers and van der Waals interactions between the neighboring polymeric backbones. While the Azo chromophore connected in the side chain of P2 induced conformation of micelles nanostructure during the CP process without any post-treatment. Furthermore, the photoisomerization of Azo units had an obviously different regulatory effect on the conjugated degree of the polymer backbone, especially for the single-stranded P2, which was attributed to the structural differences and the interaction between AB chromophores in the polymers. Full article

(This article belongs to the Special Issue Azobenzene and Applications: From Catalysis to Biology)

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