Recent advances in Norrish–Yang cyclization and dicarbonyl photoredox reactions for natural product synthesis

• Peng-Xi Luo,
• Jin-Xuan Yang,
• Shao-Min Fu and
• Bo Liu

Beilstein J. Org. Chem. 2025, 21, 2315–2333, doi:10.3762/bjoc.21.177

• , 108d) underwent the desired photochemical reaction (Scheme 13b), yielding spiroacetals 109a, 109b, and 109d following CAN (cerium(IV) ammonium nitrate) oxidation. In contrast, C7-methoxy-substituted analogs (108c, 108e) remained unreactive. Reactivity correlated with UV–vis absorption profiles

A m-quaterphenyl probe for absolute configurational assignments of primary and secondary amines

• Yuka Takeuchi,
• Mutsumi Kobayashi,
• Yuuka Gotoh,
• Mari Ikeda,
• Yoichi Habata,
• Tomohiko Shirai and
• Shunsuke Kuwahara

Beilstein J. Org. Chem. 2025, 21, 2211–2219, doi:10.3762/bjoc.21.168

• bond. Therefore, the π-electron conjugation is widespread almost over the chromophores. However, the UV spectrum of 1–ʟ-alaninol conjugate (S)-2a shows an intense absorption, maintaining the nature of methoxybiphenyl chromophore. The absorption band at 259 nm is attributed to the π–π* transition

Understanding the origin of stereoselectivity in the photochemical denitrogenation of 2,3-diazabicyclo[2.2.1]heptene and its derivatives with non-adiabatic molecular dynamics

• Leticia A. Gomes and
• Steven A. Lopez

Beilstein J. Org. Chem. 2025, 21, 2007–2020, doi:10.3762/bjoc.21.156

• , experimentally, there is an ensemble of non-equilibrium geometries. To get a more realistic understanding of the absorption, we generated 500 geometries using the Wigner-sampling method to generate an ensemble of energetically accessible non-equilibrium geometries. We computed the gas-phase vertical excitation

• energies (S0 → Sn, n = 1, 2, 3) and corresponding oscillator strengths of the Wigner-sampled structures of 1, 3 and 5 to explore the nature of electronic excitations to the FC regions. This allowed us to predict an absorption spectrum with normalized oscillator strengths (S0 → S3). Figure 2 shows the

• computed absorption spectra of 1, 3, and 5. Figure 2 shows the 1, 3, and 5 computed absorption spectra with three λmax peaks. The S0 to S3 has a peak centered from 179 to 181 nm and corresponds to a majority nNN(σCN) → Ryd, the peak centered from 190 to 194 nm corresponds to a majority nNN → π* from S0 to

Aryl iodane-induced cascade arylation–1,2-silyl shift–heterocyclization of propargylsilanes under copper catalysis

• Rasma Kroņkalne,
• Rūdolfs Beļaunieks,
• Armands Sebris,
• Anatoly Mishnev and
• Māris Turks

Beilstein J. Org. Chem. 2025, 21, 1984–1994, doi:10.3762/bjoc.21.154

• it improves lipophilicity, oral absorption and biological activity [25]. Results and Discussion Arylation of aliphatic chain-containing propargylsilanes We started our investigation with the arylation of aliphatic chain-containing propargylsilanes. The starting material – tert-butyl(hept-1-yn-3-yl

Photochemical reduction of acylimidazolium salts

• Michael Jakob,
• Nick Bechler,
• Hassan Abdelwahab,
• Fabian Weber,
• Janos Wasternack,
• Leonardo Kleebauer,
• Jan P. Götze and
• Matthew N. Hopkinson

Beilstein J. Org. Chem. 2025, 21, 1973–1983, doi:10.3762/bjoc.21.153

• catalytic photoenolization/Diels–Alder (PEDA) reaction [14][15]. In this process, the NHC fragment present in the acylazolium species influences the absorption wavelength and fundamental photochemical reactivity of the C=O bond, enabling a “ketone-like” photoreaction from otherwise unsuitable carboxylic

• identity of the active light-absorbing species in the reaction mixture. UV–vis spectra of the benzoylazolium starting material 1 at different concentrations in the acetonitrile reaction solvent were accordingly measured. Although exhibiting maximum absorption at wavelengths significantly shorter than that

• emitted by the light sources used (latest λabs,max = 271 nm), a significant absorption tail up to ca. λ = 400 nm was observed at higher concentrations, indicating that the starting material could potentially absorb the incident light directly. This rationale is consistent with the increase in reduction

Synthesis of N-doped chiral macrocycles by regioselective palladium-catalyzed arylation

• Shuhai Qiu and
• Junzhi Liu

Beilstein J. Org. Chem. 2025, 21, 1917–1923, doi:10.3762/bjoc.21.149

• absorption maximum of MC1 is more redshifted by 42 nm compared to MC2, which is attributed to the extended conjugation after the fusion of one pyrene unit. Similarly, both MC1 and MC2 have higher ΦF values of 0.45 and 0.69 than compound MC3 (ΦF = 0.13). The optical energy bandgaps were determined to be 2.48

• well as four negative Cotton effects at 288, 317, 331, and 432 nm, respectively. (−)-MC1 exhibits a mirror image with the opposite signals to that of (+)-MC1. The maximum absorption dissymmetry factor (gabs) value of 1.1 × 10−3 at 453 nm is observed (Figure 5b), which is derived from the S0→S1

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

• ). Shining light will bring the molecule to a generic excited state (which is different for different photoswitch classes and substitution patterns and will not be treated in detail), which can then relax back to the ground state in either of the two wells. In cases where the two absorption spectra of the

• ). It must be noted, though, that in literature both PSS and PSD are used to indicate the photostationary distribution [2]. We will use the PSS notation throughout the review. Often, the two absorption spectra overlap, and both isomers are excited to different extents at the same time. The extent of

• switched to another. To achieve the best PSS, a wavelength with minimum spectral overlap should be chosen, which may not correspond to the maximum absorption wavelength (Figure 2) [3]. Positive photochromism is observed when the stable isomer has a maximum absorption at the lower wavelength (i.e., UV), and

On the aromaticity and photophysics of 1-arylbenzo[a]imidazo[5,1,2-cd]indolizines as bicolor fluorescent molecules for barium tagging in the study of double-beta decay of ¹³⁶Xe

• Eric Iván Velazco-Cabral,
• Fernando Auria-Luna,
• Juan Molina-Canteras,
• Miguel A. Vázquez,
• Iván Rivilla and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2025, 21, 1627–1638, doi:10.3762/bjoc.21.126

• -cd]indolizine and the para-phenylene groups, especially in the S1 state, thus indicating that both aromatic units are coupled under excitation–relaxation to produce the corresponding absorption–emission spectra (vide infra). The calculated structures of 18 complexed with barium perchlorate are more

• + prompted us to compare the photophysical properties of unbound compound 18 in the presence of Ba(ClO4)2. The values corresponding to the adiabatic absorption (S0(optimized) → S1*, adiabatic absorption) and emission (S1(optimized) → S0, fluorescence) are reported in Table 2, together with the differences

• between the free and bound states. The corresponding signed errors are gathered in Figure 7. The behavior of the different functionals resulted to be very variable, although the ground state and excited state geometries were very similar. In the case of absorption wavelengths, wB97XD, BHandHHLYP and CAM

Synthesis of optically active folded cyclic dimers and trimers

• Ena Kumamoto,
• Kana Ogawa,
• Kazunori Okamoto and
• Yasuhiro Morisaki

Beilstein J. Org. Chem. 2025, 21, 1603–1612, doi:10.3762/bjoc.21.124

• simple SiO2 column chromatography. In addition, they were purified using a recyclable high-performance liquid chromatography (HPLC) to remove unidentified impurities to obtain (Sp)-6 and (Sp)-7 in 16% and 3% isolated yields, respectively. The ultraviolet–visible (UV–vis) absorption spectra and normalized

• photoluminescence (PL) spectra of (Sp)-6 and (Sp)-7 in diluted CHCl3 solutions (1.0 × 10−5 M) are depicted in Figure 1. The absorption bands are derived from the π–π* transitions of a phenylene–ethynylene conjugation system. The spectra of (Sp)-6 and (Sp)-7 are similar, and the absorption peak top of (Sp)-7 is red

• -shifted compared with that of (Sp)-6 because of the bent structure of the p-phenylene–ethynylene moieties in (Sp)-6 and extended π-conjugation of (Sp)-7. Such a red-shift of a UV–vis absorption spectrum has been observed in previously reported [2.2]paracyclophane-based cyclic oligomers [39]. CHCl3

Thermodynamic equilibrium between locally excited and charge transfer states in perylene–phenothiazine dyads

• Issei Fukunaga,
• Shunsuke Kobashi,
• Yuki Nagai,
• Hiroki Horita,
• Hiromitsu Maeda and
• Yoichi Kobayashi

Beilstein J. Org. Chem. 2025, 21, 1577–1586, doi:10.3762/bjoc.21.121

• the PTZ moiety and the photoinduced charge-transfer (CT) state. Femtosecond to microsecond transient absorption spectroscopy reveals that this equilibrium is facilitated not simply by enhanced donor ability, but presumably by excited-state planarization of the PTZ moiety, which lowers the energy of

• demonstrate that precise electronic and geometric design can enable controllable excited-state behavior in orthogonal molecular systems. Keywords: charge transfer; electron transfer; molecular dyad; transient absorption; Introduction Photoinduced electron transfer and charge separation are fundamental

• featuring high photostability and strong visible absorption. Perylene–phenothiazine (Pe–PTZ) derivatives have been previously investigated for their excited-state dynamics [15]. Incorporating additional electron-donating groups such as triphenylamine (TPA) onto the PTZ core is expected not only to enhance

Synthesis of an aza[5]helicene-incorporated macrocyclic heteroarene via oxidation of an o-phenylene-pyrrole-thiophene icosamer

• Yusuke Matsuo,
• Aoi Nakagawa,
• Shu Seki and
• Takayuki Tanaka

Beilstein J. Org. Chem. 2025, 21, 1561–1567, doi:10.3762/bjoc.21.119

• two NH sites remained uncoordinated due to steric hindrance. Non-covalent interaction (NCI) plot analysis revealed distinct intramolecular π–π dispersion interactions between the two aza[5]helicene moieties (green surface in Figure 4b) [29][30][31]. Optical properties The electronic absorption and

• emission spectra of 4 were measured in DMSO (Figure 5a). As observed for other o-phenylene-bridged cyclic heteroarenes in previous reports, compound 4 exhibited a broad featureless absorption band up to 450 nm, with emission peaked at 546 nm. The red-shifted emission is likely due to a significant

• structural relaxation in the excited state. The fluorescence quantum yield (ΦF) was determined as 0.078 (λex = 300 nm), and the fluorescence lifetime (τ) using biexponential decay model fitting as 1.7 and 4.4 ns. The partially fused structure of 5 exhibited a well-defined lowest-energy absorption band peaked

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

• changes in their absorption and photochemical properties. While azobenzene protonation has been recently used as a tool in photoswitching studies, the factors influencing protonation itself have received little attention. Here, we report a strong temperature dependence of azobenzene protonation in 1,2

• they all typically result in significant changes in the absorption spectrum and/or alter the stability of the metastable isomer. In sensing, azobenzenes have been utilized, e.g., through changes in isomerization kinetics [17][18] or colorimetric properties. The colorimetric sensors are effective for

• and protonated species. Protonation leads to a notable red-shift in the absorption spectrum from 320–360 nm to 420–510 nm, as shown in Figure 1B using methanesulfonic acid (MSA) in 1,2-dichloroethane (DCE). We assume that in DCE alone, no protonation occurs. In MSA, on the other hand, full protonation

Microwave-enhanced additive-free C–H amination of benzoxazoles catalysed by supported copper

• Andrei Paraschiv,
• Valentina Maruzzo,
• Filippo Pettazzi,
• Stefano Magliocco,
• Paolo Inaudi,
• Daria Brambilla,
• Gloria Berlier,
• Giancarlo Cravotto and
• Katia Martina

Beilstein J. Org. Chem. 2025, 21, 1462–1476, doi:10.3762/bjoc.21.108

• its moderate absorption capacity and specific surface area (SSA), measured at 164 m2/g using the BET surface area analysis, and because it can be efficiently derivatised with a trialkoxysilane amino derivative as recently reported [61]. A previously optimised ultrasound-promoted synthetic protocol was

• δNH2, at around 3370, 3300 and 1596 cm−1, respectively) and by the νCH2 and δCH2 vibrations (curve a) [64][65]. The broad absorption in the high frequency region is characteristic of hydrogen bonding between Si–OH and NH2 groups in functionalised silica materials. After insertion of Cu(I), small

Wittig reaction of cyclobisbiphenylenecarbonyl

• Taito Moribe,
• Junichiro Hirano,
• Hideaki Takano,
• Hiroshi Shinokubo and
• Norihito Fukui

Beilstein J. Org. Chem. 2025, 21, 1454–1461, doi:10.3762/bjoc.21.107

• racemization barrier. Optical and chiroptical properties The UV–vis absorption spectra of CBBC 1, mono-olefin 3, and bis-olefin 5 are shown in Figure 5a. The absorption of 3 tails to 370 nm, which is comparable to the absorption end of CBBC 1. On the other hand, the absorption of bis-olefin 5 is blue-shifted

• , tailing to 325 nm. In the case of CBBC 1, the contribution of n–π* transition due to the carbonyl groups affords weak absorption in the 300–380 nm range [17]. Consequently, the blue-shifted absorption of 5 compared to those of 1 and 3 could result from the loss of carbonyl groups. The relatively large

• the axial chirality of the biaryl segments, respectively. (a) UV–vis absorption (solid lines) and emission (dashed lines) spectra of 1 (black), 3 (blue), and 5 (red). (b) CD spectra of 1 (black), 3 (blue), and 5 (red). (c) CD g values of 1 (black), 3 (blue), and 5 (red). λ = wavelength; ε = extinction

Advances in nitrogen-containing helicenes: synthesis, chiroptical properties, and optoelectronic applications

• Meng Qiu,
• Jing Du,
• Nai-Te Yao,
• Xin-Yue Wang and
• Han-Yuan Gong

Beilstein J. Org. Chem. 2025, 21, 1422–1453, doi:10.3762/bjoc.21.106

• core [17]. Compared to 4a, compound 4b exhibits bathochromic shifts of 12 nm in absorption and 45 nm in emission, as well as a higher ΦF (0.75 vs 0.68). Both isomers display TADF at room temperature and phosphorescence at 77 K. Notably, 4a demonstrates a long-lived red afterglow persisting for up to 30

• absorption and emission maxima (λabs = 399 nm, λem = 405 nm), a fluorescence quantum yield (ΦF) of 0.13, and high dissymmetry factors (|gabs| = 1.9 × 10−2, |gabs| = 9.5 × 10−3 at 403 nm) [18] (Table 2). Miura and co-workers employed Pd(II)/Ag(I)-catalyzed cyclizations to construct azahelicenes, with compound

• intramolecular Scholl reactions [24] (Table 3). All compounds exhibited strong absorption in the UV–vis region (250–450 nm) and fluorescence emission between 400–550 nm. Among these, compound 11c, a saddle-shaped dibenzodiaza[8]circulene, was particularly noteworthy as the first example of its kind synthesized

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

• /mol). Of course, the best way to validate the theoretical data for compound 1 is to study its tautomerism experimentally. The simulated absorption spectra of 1 are shown in Figure 1, while the experimental spectra in various solvents are given in Figure 2. It is obvious from the latter that solvent

• and KK (both below 5%) could be observed in amounts around the detection limit of optical spectroscopy, which finally should not lead to substantial spectral changes comparing to toluene. The absorption spectra, shown in Figure S10 (Supporting Information File 1), suggest a different story. The

• of its existing amount and, consequently, to rise of the absorption band at around 470 nm and restoration with the time of the equilibrium tautomeric state. No appearance of K is expected as a result of higher energy as discussed previously. Actually, the third process is shown in Figure 7. Upon

Reactions of acryl thioamides with iminoiodinanes as a one-step synthesis of N-sulfonyl-2,3-dihydro-1,2-thiazoles

• Vladimir G. Ilkin,
• Pavel S. Silaichev,
• Valeriy O. Filimonov,
• Tetyana V. Beryozkina,
• Margarita D. Likhacheva,
• Pavel A. Slepukhin,
• Wim Dehaen and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2025, 21, 1397–1403, doi:10.3762/bjoc.21.104

• irradiation, graphite monochromator, ω-scanning in 1° increments at T = 295(2) K). An empirical correction for absorption has been introduced. Using the Olex2 [23] software shell, the structure was solved using the SHELXT program and refined using the SHELXL [24][25] program with a full-matrix F2 MNC for non

Recent advances and future challenges in the bottom-up synthesis of azulene-embedded nanographenes

• Bartłomiej Pigulski

Beilstein J. Org. Chem. 2025, 21, 1272–1305, doi:10.3762/bjoc.21.99

• due to the dominance of surrounding benzenoid rings or the presence of biradical character. As a result, these PAHs despite, possessing formal azulene may exhibit properties typical of benzenoid molecules rather than the characteristic azulene features such as red-shifted absorption, a small HOMO–LUMO

• ]indene (6) as black plates in a 32% yield. The azulene-containing isomers of pyrene exhibit azulene-like absorption tailing up to around 650 nm. Interestingly, despite their initial synthesis in the 1950s, no further attempts have been made to synthesize compounds 2 and 6 using more modern methods

• employed by Hara and co-workers in 1975 (Scheme 3) [37]. Compound 19 reacted with cyanine 20 to give pentafulvene 21. Compound 21 was later cyclized in quinoline at 180 °C giving non-alternant isomer of benzo[a]pyrene 22 in 62% isolated yield. PAH 22 has remarkable re-shifted optical absorption with λmax

Recent advances in synthetic approaches for bioactive cinnamic acid derivatives

• Betty A. Kustiana,
• Galuh Widiyarti and
• Teni Ernawati

Beilstein J. Org. Chem. 2025, 21, 1031–1086, doi:10.3762/bjoc.21.85

• (TXA2) synthetase inhibition [10], antinociceptive [11], histone deacetylase inhibition [12], α-glucosidase inhibition [13] , tyrosinase inhibition [14], allelochemical [15], anticonvulsant [16], antioxidant [17], antiplatelet aggregation [18], anti-inflammatory [19], and UV absorption [20]. Cinnamic

Biobased carbon dots as photoreductants – an investigation by using triarylsulfonium salts

• Valentina Benazzi,
• Arianna Bini,
• Ilaria Bertuol,
• Mariangela Novello,
• Federica Baldi,
• Matteo Hoch,
• Alvise Perosa and
• Stefano Protti

Beilstein J. Org. Chem. 2025, 21, 1024–1030, doi:10.3762/bjoc.21.84

• via hydrothermal treatments have an amorphous structure. The optical properties of the prepared CDs were thus investigated by UV–vis absorption spectroscopy. The obtained spectra (Figure 1) showed three main absorption bands located at 225–235 nm (assigned to, according to the literature, the π–π

• predominant band located at 350 nm, CDs synthesized from glucose and bass scales show a significant absorption at around 260 nm and 300 nm, respectively [33][34][35]. A different UV–vis spectrum was obtained for the Blackberries-derived nitrogen-doped material, which showed a main absorption at 330 nm, with a

Synthesis of pyrrolo[3,2-d]pyrimidine-2,4(3H)-diones by domino C–N coupling/hydroamination reactions

• Ruben Manuel Figueira de Abreu,
• Robin Tiedemann,
• Peter Ehlers and
• Peter Langer

Beilstein J. Org. Chem. 2025, 21, 1010–1017, doi:10.3762/bjoc.21.82

• Abstract A variety of pyrrolo[3,2-d]pyrimidine-2,4(3H)-diones were prepared by a combination of Sonogashira reaction and subsequent cyclization by domino C–N coupling/hydroamination reaction. The optical properties (UV–vis absorption and fluorescence) depend on the substitution pattern of the compounds

• ]pyrimidine-2,4(3H)-diones 4 were investigated by steady-state absorption and photoluminescence spectroscopy (Figure 2, Table 2). The wavelength and intensity of absorption and emission depended on the substitution pattern. The methyl-substituted compound 4a showed one broad absorption band at ≈290 nm. A

• similar absorption feature, but slightly bathochromically shifted, was observed for the thienyl-substituted derivative 4m. The strongly electron-donating N,N-dimethylaminophenyl group (products 4k,l) resulted in segmentation into two absorption bands accompanied by a strongly red-shifted lower energy

On the photoluminescence in triarylmethyl-centered mono-, di-, and multiradicals

• Daniel Straub,
• Markus Gross,
• Mona E. Arnold,
• Julia Zolg and
• Alexander J. C. Kuehne

Beilstein J. Org. Chem. 2025, 21, 964–998, doi:10.3762/bjoc.21.80

• , there is a lack of understanding of why the absorption and photoluminescence of D3 symmetrical triphenylmethyl radicals are so weak in the visible spectrum. While it is understood that the functionalization with donor moieties breaks the D3 symmetry, the ϕ varies greatly among different donors and also

• . Only at temperatures as low as 90 K, the monoradical is stable, allowing recording of the absorption and emission spectra [30]. Symmetrical halogenation of the triphenylmethyl (or trityl) unit increases stability of the molecule, compared to the parent unsubstituted trityl radical first reported by

• –LUMO energy gaps are identical and their respective transitions exhibit identical transition dipole moments [19][32][33]. For the |D1⟩ transition these two degenerate transitions mix in an out-of-phase fashion leading to the observed weak absorption at 544 nm (see Figure 1b and c). When looking at the

Study of tribenzo[b,d,f]azepine as donor in D–A photocatalysts

• Katy Medrano-Uribe,
• Jorge Humbrías-Martín and
• Luca Dell’Amico

Beilstein J. Org. Chem. 2025, 21, 935–944, doi:10.3762/bjoc.21.76

• absorption profile in the visible region, ii) a long lifetime of the excited states, and iii) balanced redox potentials in both the ground and excited states [7]. In 2018, Zeitler and her collaborators conducted an innovative and in-depth study on modulating the photochemical properties of a family of donor

• 6a, we observed a blue-shifted absorption profile due to the break of the conjugation in sulfur-based acceptors. Compounds 4a and 6a presented a similar absorption profile, while molecule 5a showed a red-shifted spectrum tailing up to the visible region (Figure 2a). The lack of a significant charge

• electron-withdrawing group [31]. Additionally, it is possible that the mobility of core 4 contributes to this behavior, as evidenced by the observation that the DE is not present in the more rigid structures 5a and 6a. In this compound, we did not observe changes in the absorption profile during the

Light-enabled intramolecular [2 + 2] cycloaddition via photoactivation of simple alkenylboronic esters

• Lewis McGhie,
• Hannah M. Kortman,
• Jenna Rumpf,
• Peter H. Seeberger and
• John J. Molloy

Beilstein J. Org. Chem. 2025, 21, 854–863, doi:10.3762/bjoc.21.69

• solvent had a profound effect on reactivity with more Lewis-basic solvents suppressing reactivity (Table 1, entries 4 and 5 vs entries 6 and 7), indicating p-orbital availability plays a prominent role [56][57]. A control reaction (Table 1, entry 8), in combination with UV–vis absorption studies (see

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

• examples. Azobenzene and its derivatives show two characteristic absorption bands, namely a π→π* transition around 330 nm and an n→π* one around 450 nm, respectively [22]. The molecule can populate the thermodynamically metastable Z isomer by addressing these transitions in the thermally stable E form. The

• relative position of the absorption bands in the azobenzene derivatives depends on the substitution pattern on the aromatic rings, which can act as a handle to affect the absorption properties of the compound class [3]. For instance, push–pull systems or the introduction of tetra-ortho substituents were

• reported to either bathochromically shift the UV–vis absorption spectrum or lead to a better separation of the n→π* bands of the two photoisomers and allow for visible-light-responsive switches [23][24][25][26]. In recent years, heteroaryl azobenzene derivatives have revealed superior properties to