Rotaxanes with integrated photoswitches: design principles, functional behavior, and emerging applications

• Jullyane Emi Matsushima,
• Khushbu,
• Zuliah Abdulsalam,
• Udyogi Navodya Kulathilaka Conthagamage and
• Víctor García-López

Beilstein J. Org. Chem. 2025, 21, 2345–2366, doi:10.3762/bjoc.21.179

• photophysical properties [56]. Contrary to azobenzenes, where the isomerization modulates the position of the macrocycle, in dithienylethene-based rotaxanes, it is the shuttling of the macrocycle that modulates the fluorescence and photoswitching behavior of the dithienylethene. For example, Yin and co-workers

• structural differences, fumaramide switches operate similarly to azobenzenes in rotaxanes, utilizing light-induced trans–cis isomerization to control the macrocycle shuttling [62]. Leigh and co-workers developed the first furmaramide-based rotaxanes, in which the photoswitchable unit was incorporated into

• , Yang and co-workers reported a [2]rotaxane featuring a macrocycle constructed from two azobenzene photoswitches threaded onto an asymmetric axle [89]. Photoisomerization of the azobenzenes alters the geometry and size of the macrocycle, thereby modulating its affinity toward two distinct recognition

Pd-catalyzed dehydrogenative arylation of arylhydrazines to access non-symmetric azobenzenes, including tetra-ortho derivatives

• Loris Geminiani,
• Kathrin Junge,
• Matthias Beller and
• Jean-François Soulé

Beilstein J. Org. Chem. 2025, 21, 2234–2242, doi:10.3762/bjoc.21.170

• Paris, France 10.3762/bjoc.21.170 Abstract Azobenzenes are photoresponsive compounds widely used in molecular switches, light-controlled materials, and sensors, but despite extensive studies on symmetric derivatives, efficient methods for synthesizing non-symmetric analogues remain scarce due to

• regioselectivity issues, multistep procedures, and limited applicability to tetra-ortho-substituted structures. Herein, we describe a direct, one-pot Pd-catalyzed dehydrogenative C–N coupling between aryl bromides and arylhydrazines to access non-symmetric azobenzenes. The use of bulky phosphine ligands and

• sterically tuned substrates promotes selective N-arylation at the terminal nitrogen. The protocol tolerates a wide range of functional groups and enables the synthesis of well-decorated azobenzenes, including tetra-ortho-substituted derivatives. Notably, the reaction proceeds under an O2 atmosphere and in

Solar thermal fuels: azobenzene as a cyclic photon–heat transduction platform

• Jie Yan,
• Shaodong Sun,
• Minghao Wang and
• Si Wu

Beilstein J. Org. Chem. 2025, 21, 2036–2047, doi:10.3762/bjoc.21.159

• transition behavior, achieving high gravimetric energy densities (300–400 J/g) with long-term storage stability (Figure 6d). Grossman and Durgun proposed methods for incorporating azobenzenes into macrocyclic structures [82]. Their computational models indicated that the molecular rings connecting the

Photoswitches beyond azobenzene: a beginner’s guide

• Michela Marcon,
• Christoph Haag and
• Burkhard König

Beilstein J. Org. Chem. 2025, 21, 1808–1853, doi:10.3762/bjoc.21.143

• ; synthesis of photoswitches; switching mechanisms; tutorial review; Introduction Photophysical properties and switching mechanism Key learning points Switching mechanisms and the change in properties. Overview of the major classes of photoswitches beyond azobenzenes. Main synthetic pathways for their

• individual features that may render them more suitable for applications than azobenzenes. This review, particularly for those new to the field, aims to summarise the classes of azoheteroarenes, diazocines, indigoids, arylhydrazones, diarylethenes, fulgides, and spiropyrans concerning their photophysical

• picoseconds to several years. The presence of heteroatoms also introduces H-bond donors and acceptors and metal coordination sites [11]. Like azobenzenes, E–Z isomerisation of azoheteroarenes can be triggered by light irradiation, while Z–E isomerisation proceeds through irradiation with a different

Azobenzene protonation as a tool for temperature sensing

• Antti Siiskonen,
• Sami Vesamäki and
• Arri Priimagi

Beilstein J. Org. Chem. 2025, 21, 1528–1534, doi:10.3762/bjoc.21.115

• Antti Siiskonen Sami Vesamaki Arri Priimagi Smart Photonic Materials, Faculty of Engineering and Natural Sciences, Tampere University, Korkeakoulunkatu 3, FI-33720 Tampere, Finland 10.3762/bjoc.21.115 Abstract Azobenzenes can be protonated at one of the azo nitrogen atoms, leading to significant

• emerged as staple building blocks in smart materials, from light-responsive norbornadienes in molecular solar thermal energy storage [2] to pH-sensitive spiropyrans in cell imaging [3], and redox-active viologens in memory junctions [4]. Among the different molecular switches azobenzenes stand out due to

• azobenzene core by introducing different functional groups to the phenyl rings. For these reasons, azobenzenes can be sensitized to various stimuli and easily integrated into different types of materials. While cis–trans isomerization is the most prominent property of interest for azobenzenes, there are also

Tautomerism and switching in 7-hydroxy-8-(azophenyl)quinoline and similar compounds

• Lidia Zaharieva,
• Vera Deneva,
• Fadhil S. Kamounah,
• Nikolay Vassilev,
• Ivan Angelov,
• Michael Pittelkow and
• Liudmil Antonov

Beilstein J. Org. Chem. 2025, 21, 1404–1421, doi:10.3762/bjoc.21.105

• azobenzenes [61][62][63][64][65][66][67][68][69][70][71][72][73][74], the number of studies, dealing with the excited-state behavior of compounds where an OH group is situated on the ortho position in respect of the azo group, is very limited. It is not surprising because in these cases a possibility for

• to the low basicity of the proton-accepting nitrogen atom, the KE* form spontaneously goes to E*, which closes the channel to the twisting region. On the other side there is substantial number of papers describing the very long-lived cis isomers in ortho-halogen-substituted azobenzenes [38][85][86

Substituent effects in N-acetylated phenylazopyrazole photoswitches

• Radek Tovtik,
• Dennis Marzin,
• Pia Weigel,
• Stefano Crespi and
• Nadja A. Simeth

Beilstein J. Org. Chem. 2025, 21, 830–838, doi:10.3762/bjoc.21.66

• discovered that simple acylation of the pyrazole moiety leads to increased quantum yields of isomerization, long Z-isomer life-times, good spectral separation, and high photostability. Keywords: azobenzenes; azopyrazoles; photochromism; photoswitches; substituent effects; Introduction Organic photoswitches

• have been described and extensively studied [1][2]. Among these, azobenzenes belong to the most common ones [3]. They were firstly explored almost 200 years ago [4] and initially used mainly as dyes or pigments [5]. Relatively recently, azobenzenes started to become an important part of state-of-the

• classical azobenzenes. Heterocyclic rings offer, for example, enhanced polarity, electron pairs for metal coordination [27], better water-solubility, and variable pKa [28][29]. Special attention has been given to 5-membered N-heterocyclic azobenzenes, which not only maintain the azobenzenes properties but

Synthesis and photoinduced switching properties of C₇-heteroatom containing push–pull norbornadiene derivatives

• Daniel Krappmann and
• Andreas Hirsch

Beilstein J. Org. Chem. 2025, 21, 807–816, doi:10.3762/bjoc.21.64

• heat, catalysis, or an electrochemical input [4][5][6], the stored energy can be released converting the molecule back in the parent form (Figure 1). Typical MOST systems are azobenzenes (E/Z-isomerization) [7][8][9][10], the isomerization of dihydroazulenes/vinylheptafulvenes [11][12][13], conversion

Synthesis of N-acetyl diazocine derivatives via cross-coupling reaction

• Thomas Brandt,
• Pascal Lentes,
• Jeremy Rudtke,
• Michael Hösgen,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2025, 21, 490–499, doi:10.3762/bjoc.21.36

• Abstract Diazocines are photoswitches derived from azobenzenes by bridging the two phenyl rings in ortho position with a CH2CH2 group forming an eight membered (diazocine) ring. Diazocine is superior to most azobenzenes in almost all photophysical properties (switching efficiency, quantum yield

• azobenzenes, spiropyranes and diarylethenes in organic solvents [3][13][15]. There are two strategies of applying diazocines in photopharmacology. The first one exploits the structural similarity of the tricyclic diazocine framework to the tricyclic structure of, e.g., tetrahydrodibenzazocines [16][17] and

• examples of last-step modifications of azobenzenes via Suzuki–Miyaura reactions in the current literature, which indicate that the reaction conditions are compatible with azo groups [27][28]. Suzuki–Miyaura reaction of 2 and 3 with different phenylboronic acids resulted in the formation of the

Effect of substitution position of aryl groups on the thermal back reactivity of aza-diarylethene photoswitches and prediction by density functional theory

• Misato Suganuma,
• Daichi Kitagawa,
• Shota Hamatani and
• Seiya Kobatake

Beilstein J. Org. Chem. 2025, 21, 242–252, doi:10.3762/bjoc.21.16

• -withdrawing substituents on the N-aryl moieties enhanced the thermal stability of the Z-isomers while maintaining the advantageous photoswitching properties upon irradiation with red light [52]. The effect of substituents on the thermal cis–trans isomerization of azobenzenes has also been widely studied, and

• time scale [54]. Langton and co-workers demonstrated that the thermal isomerization rate of azobenzenes can be tuned over a time scale spanning 107 seconds by introducing appropriate chalcogens and halogens at the ortho-position of the benzene rings [55]. Thus, investigation of the strategies to

Extension of the π-system of monoaryl-substituted norbornadienes with acetylene bridges: influence on the photochemical conversion and storage of light energy

• Robin Schulte,
• Dustin Schade,
• Thomas Paululat,
• Till J. B. Zähringer,
• Christoph Kerzig and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 3061–3068, doi:10.3762/bjoc.20.254

• ], azobenzenes [16][17][18][19], dihydroazulenes [20][21], or azaborines [22][23]. However, the most prominent feasible MOST system is the [2 + 2] photocycloaddition–cycloreversion cycle between norbornadiene (1a) and quadricyclane (2a), which has several advantageous properties (Scheme 1) [8][14][24]. In

Supramolecular assemblies of amphiphilic donor–acceptor Stenhouse adducts as macroscopic soft scaffolds

• Ka-Lung Hung,
• Leong-Hung Cheung,
• Yikun Ren,
• Ming-Hin Chau,
• Yan-Yi Lam,
• Takashi Kajitani and
• Franco King-Chi Leung

Beilstein J. Org. Chem. 2024, 20, 1590–1603, doi:10.3762/bjoc.20.142

• -driven supramolecular assemblies on a microscopic length scale, such as those containing spiropyrans, azobenzenes, and indigos, have been used in transformations in aqueous medium [35][45][46]. However, very few examples of visible-light-driven supramolecular transformation on a macroscopic length scale

Photoswitchable glycoligands targeting Pseudomonas aeruginosa LecA

• Yu Fan,
• Ahmed El Rhaz,
• Stéphane Maisonneuve,
• Emilie Gillon,
• Maha Fatthalla,
• Franck Le Bideau,
• Guillaume Laurent,
• Samir Messaoudi,
• Anne Imberty and
• Juan Xie

Beilstein J. Org. Chem. 2024, 20, 1486–1496, doi:10.3762/bjoc.20.132

• photoswitchable tools, few photochromic lectin ligands have been developed. We have designed and synthesized several O- and S-galactosyl azobenzenes as photoswitchable ligands of LecA and evaluated their binding affinity with isothermal titration calorimetry. We show that the synthesized monovalent glycoligands

• due to stronger unfavorable entropy, they are in general of lower affinity. The validation of this proof-of-concept and the dissection of thermodynamics of binding will help for the further development of lectin ligands that can be controlled by light. Keywords: carbohydrates; glycosyl azobenzenes

• [11][12][13][14][15][16][17][18]. The group of Lindhorst has reported a series of mannosyl azobenzenes targeting E. coli lectin FimH, demonstrating the possibility to control the type 1 fimbriae-mediated bacterial adhesion to a self-assembled monolayer of mannosyl azobenzene on a gold surface [19][20

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C–O bonds in organic transformations

• Mithu Roy,
• Bitan Sardar,
• Itu Mallick and
• Dipankar Srimani

Beilstein J. Org. Chem. 2024, 20, 1348–1375, doi:10.3762/bjoc.20.119

• hydroacylation of azobenzenes employing acids as hydroacylating reagents (Scheme 4). The reaction progressed smoothly, involving the cleavage of the C–O bond using a photogenerated phosphoranyl radical. The methodology demonstrated an excellent compatibility with a wide range of azobenzenes and carboxylic acids

• azobenzenes with carboxylic acids. Photoredox-catalyzed synthesis of flavonoids. Synthesis of O-thiocarbamates and photocatalytic reduction of O-thiocarbamates. Deoxygenative borylation of alcohols. Trifluoromethylation of O-alkyl thiocarbonyl substrates. Redox-neutral radical coupling reactions of alkyl

Novel route to enhance the thermo-optical performance of bicyclic diene photoswitches for solar thermal batteries

• Akanksha Ashok Sangolkar,
• Rama Krishna Kadiyam and
• Ravinder Pawar

Beilstein J. Org. Chem. 2024, 20, 1053–1068, doi:10.3762/bjoc.20.93

• /vinylheptafulvene, azobenzenes, tetracarbonyl(fulvalene)diruthenium complexes, norbornadiene/quadricyclane (NBD/QC), anthracenes, etc. exhibit a few promising properties for MOST applications [10][12][13]. However, these photoswitching couples still lack one or more important properties required in MOST systems and

Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

Dissecting Mechanochemistry III

• Lars Borchardt and
• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1454–1456, doi:10.3762/bjoc.18.150

• were also key reagents to develop the mechanochemical halogenation of azobenzenes as studied by Ćurić and co-workers [4]. They demonstrated how, depending on the azobenzene structure, the halogenation of the C–H bonds with NBX occurred in the presence of Pd(II) catalysts or under metal-free conditions

• José G. Hernández Bochum, Medellín, October 2022 ORCID® iDs Lars Borchardt - https://orcid.org/0000-0002-8778-7816 José G. Hernández - https://orcid.org/0000-0001-9064-4456 a) Mechanochemical PEG-400-assisted halogenation of phenols and anilines using NXS. b) Halogenation of azobenzenes with NXS

Continuous flow synthesis of azobenzenes via Baeyer–Mills reaction

• Jan H. Griwatz,
• Anne Kunz and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2022, 18, 781–787, doi:10.3762/bjoc.18.78

• Azobenzene, as one of the most prominent molecular switches, is featured in many applications ranging from photopharmacology to information or energy storage. In order to easily and reproducibly synthesize non-symmetric substituted azobenzenes in an efficient way, especially on a large scale, the commonly

• . Keywords: azobenzenes; Baeyer–Mills reaction; continuous flow; molecular switches; solar fuel; Introduction Although the red-colored azobenzenes (AB) have been known for years as dyes, their applications nowadays span from energy and information storage [1][2][3][4][5], organocatalysis [6], photobiology

• reliable synthesis of symmetric ABs in high yields via a Cu-catalyzed oxidative coupling of aniline derivatives [17]. This synthesis can be also used for the formation of non-symmetric AB, however, only for a selected set of anilines. One of the most applied methods to access non-symmetric azobenzenes is

Mechanochemical halogenation of unsymmetrically substituted azobenzenes

• Dajana Barišić,
• Mario Pajić,
• Ivan Halasz,
• Darko Babić and
• Manda Ćurić

Beilstein J. Org. Chem. 2022, 18, 680–687, doi:10.3762/bjoc.18.69

• Dajana Barisic Mario Pajic Ivan Halasz Darko Babic Manda Curic Division of Physical Chemistry, Ruđer Bošković Institute, Bijenička cesta 54, Zagreb, Croatia 10.3762/bjoc.18.69 Abstract The direct and selective mechanochemical halogenation of C–H bonds in unsymmetrically substituted azobenzenes

• proceeds by electrophilic cleavage with neutral NBS or the hydrogen bond complex NBS∙∙∙TsOH as a bromine source. Here we present the mechanochemical selective halogenation of unsymmetrically substituted azobenzenes by NXS (X = Cl, Br, or I). The liquid-assisted grinding of para-halogenated derivatives of

• azobenzene with NXS and Pd(OAc)2 as precatalyst in the presence of TsOH and MeCN as solid and liquid additives, respectively, led to the ortho-halogenated products relative to the azo group of the azobenzenes. In situ Raman monitoring of these reactions confirmed that the most favorable reaction pathway is

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• the reaction of 2-substituted indoles with azobenzenes proceeded smoothly in the presence of the chiral phosphoric acid catalyst (R)-CPA 9. At a catalyst loading of 0.2 mol %, the intermediate I-5 was simultaneously cyclized to I-6, followed by β-H elimination and chirality transfer to afford another

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• organometallic chemistry and catalysis [128]. The first example of a stoichiometric manganese-mediated C–H activation, reported by Stone, Bruce, and co-workers (1970) [129], was an ortho-metalation in azobenzenes. In recent years, with the expansion of the C–H activation field, manganese catalysts have been

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• azobenzenes was unveiled [1], manganese catalysts have exhibited a significant capacity for powerful C–H functionalization, and they have therefore been actively utilized in the area of sustainable organic syntheses [2][3][4][5][6]. Catalytic late-stage C–H functionalization, a highly efficient synthetic

Substituted nitrogen-bridged diazocines

• Pascal Lentes,
• Jeremy Rudtke,
• Thomas Griebenow and
• Rainer Herges

Beilstein J. Org. Chem. 2021, 17, 1503–1508, doi:10.3762/bjoc.17.107

• Diazocines (bridged azobenzenes) are frequently used photoswitches with outstanding photophysical properties. Parent diazocine (CH2–CH2-bridged) exhibits well-separated n–π* transitions, which allow excellent photoconversion between the Z and E configurations ((Z→E)385 nm = 92%, (E→Z)525 nm > 99% in n-hexane

• ) with light in the visible region [1]. Moreover, the Z-boat configuration is the thermodynamically stable isomer [2][3][4][5][6][7][8][9]. The latter property (i.e., the inverted stability compared to azobenzenes) makes them promising candidates for applications in photopharmacology. In the majority of

• azobenzene-based photopharmacophores, the bent Z configuration is biologically inactive [10][11][12]. Hence, (and in contrast to azobenzenes) the thermodynamically stable and biologically inactive Z-isomer can be administered and switched on with light at the site of interest with spatiotemporal resolution

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• following several approaches using a variety of photochromic systems. Feringa et al. recently published a review including systems based on double bond isomerizations [1]. An earlier review from the same group summarized light and redox responsive catalytic systems including azobenzenes, diarylethenes

• of the background reaction without catalyst is low, and the influence of the solvent on the reaction rate is small [10][32]. No catalytic effect for the N=N functional group of azobenzenes was previously observed in similar systems [10]. Ni-porphyrin Ni-TPPF20 8 (without azopyridine substitution

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147