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

• demonstrated the efficient sensitization of an alkene-containing four boron substituents using Ir(ppy)3 as a suitable sensitizer in the presence of styrene, indicating a prominent role of the adjacent p-orbital [51]. While simple alkenylboronic esters have been employed as triplet diradical quenchers to

• interactions to achieve directionality (E→Z), synonymous with conventional photocatalyzed isomerization processes [19], it serves as a rapid reaction probe to support sensitization via the generation of a photostationary state equilibrium. The use of Ir(ppy)3 (Table 1, entry 1), an efficient sensitizer for the

• activation of polyboronated alkenes [51] and β-borylstyrenes [43][48], was ineffective and no reactivity was observed. Implementing a higher energy iridium sensitizer (≈60 kcal/mol) was also unsuccessful (Table 1, entry 2), however, employing thioxanthone (65 kcal/mol) demonstrated efficient activation of

Red light excitation: illuminating photocatalysis in a new spectrum

• Lucas Fortier,
• Corentin Lefebvre and
• Norbert Hoffmann

Beilstein J. Org. Chem. 2025, 21, 296–326, doi:10.3762/bjoc.21.22

• therapeutic methods [78][79][80]. Such reactions can be performed at particular locations such as DNA or tubulin, when the photocatalyst is placed via a tethered ligand (Scheme 17) [81]. In the present case, the triarylmethine dye 67 was used as sensitizer. It is in equilibrium with the lactone form 68 and

• formed. This reaction only occurs close to the photocatalyst or sensitizer fixed at the intracellular target, for example at tubulin. An intramolecular Diels–Alder reaction followed by nitrogen extrusion

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

• alkynylbenzene and alkynylnaphthalene core is also feasible. Quenching experiments of [Ru(phen)3](PF6)2 (triplet energy ET = 2.19 eV [39]) with 1i in acetonitrile yielded a triplet energy transfer rate of kEnT = 5.8 × 109 M−1 s−1 indicating very efficient deactivation of the triplet sensitizer (Figure S4 in

• reactions of 1i and 1l (20 µM) were investigated in the presence of [Ru(phen)3](PF6)2 (20 µM) at λex = 520 nm in acetonitrile (Scheme 4). This solvent was required because of the solubility of the sensitizer. Under these conditions, both derivatives 1i and 1l showed the same development of absorption

• ] (Figure S41 in Supporting Information File 1). With this experiment, it was shown unambiguously that 1i was quantitatively converted into the corresponding quadricyclane 2i in the presence of the triplet sensitizer, as clearly indicated by the exclusive formation of the NMR signals of the photoproduct 2a

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• catalyst in the sulfonylation/arylation of styrenes and as a triplet sensitizer in energy transfer catalysis. The singlet lifetime is sufficiently long to exploit the exceptional excited state reduction potential for the activation of 4-cyanopyridine. Photoinduced electron transfer generating the radical

• spectrum (Figure 4D). For the ΦISC determination described below, we assume a cage escape quantum yield of 100%, which is reasonable for the photoinduced electron transfer between a heavy atom-free sensitizer-quencher pair in the triplet manifold [67][68][81]. Quenching of the short-lived singlet excited

• of cinnamyl chloride using Aza-H as the triplet sensitizer. See Supporting Information File 1 for details. Left: Reaction mechanism of the 3-CR with Aza-H as the photocatalyst. Potentials are given vs SCE. Right: Isomerization of stilbene using Aza-H as triplet sensitizer. Supporting Information

(Bio)isosteres of ortho- and meta-substituted benzenes

• H. Erik Diepers and
• Johannes C. L. Walker

Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78

• in moderate to good yields, employing 2,7-dimethoxythioxanthone (2,2’-OMeTX) as a triplet sensitizer for BCB excitation (Scheme 3A) [38]. Starting from BCB 24, alkenes including styrene derivatives, enol ethers, and vinyl boronates could be incorporated to give 1,2-BCHs (±)-25a–d. Brown and co

• -workers adopted a similar intramolecular [2 + 2] cycloaddition using benzophenone as a triplet sensitizer to access 1,5-BCHs (±)-59a–e as racemic mixtures of endo:exo diastereomers (Scheme 5A) [42]. Basic hydrolysis of the ester moiety followed by recrystallisation gave the diasteromerically pure acid

Synthesis of new representatives of A₃B-type carboranylporphyrins based on meso-tetra(pentafluorophenyl)porphyrin transformations

• Victoria M. Alpatova,
• Evgeny G. Rys,
• Elena G. Kononova and
• Valentina A. Ol'shevskaya

Beilstein J. Org. Chem. 2024, 20, 767–776, doi:10.3762/bjoc.20.70

• )sensitizers that are efficient for both PDT and boron neutron capture therapy (BNCT) [27][39]. The preparation of compounds with dual therapeutic efficiency is of great importance since they improve the therapeutic effect of sensitizer by the action on the different cellular sites. Here, we report the

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations

• Laura Abella,
• Gerard Novell-Leruth,
• Josep M. Ricart,
• Josep M. Poblet and
• Antonio Rodríguez-Fortea

Beilstein J. Org. Chem. 2024, 20, 92–100, doi:10.3762/bjoc.20.10

• the reaction either via singlet excitation or via radical cation formation (Scheme 1). Estimation of the activation barrier for the [2 + 2] cycloaddition when the nanotube acts as a sensitizer is 33.5 ± 6.8 kJ mol−1. This value agrees with computational predictions for the reaction via an excited

Quinoxaline derivatives as attractive electron-transporting materials

• Zeeshan Abid,
• Liaqat Ali,
• Sughra Gulzar,
• Faiza Wahad,
• Raja Shahid Ashraf and
• Christian B. Nielsen

Beilstein J. Org. Chem. 2023, 19, 1694–1712, doi:10.3762/bjoc.19.124

• -quinoxaline (PFQ) in sensitizer Qx43 resulted in exceptional PCE of 12.5%, surpassing traditional acceptor materials such as benzothiadiazole. Additionally, the improved charge recombination and stability indicate the strategic advantage of employing the right Qx derivatives for enhanced DSSC durability [45

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

• quenched photosensitizers can also limit the whole system in photochemical carbon dioxide reduction [28]. In the study, the driving force for reduction of an oxidized sensitizer was varied by using a series of photosensitizers with tunable oxidation potentials. They found that the turnover of the carbon

• dioxide reduction system was limited by the rate of the photooxidized sensitizer re-reduction. In their review of sacrificial electron donors for solar fuels, Pellegrin and Odobel noted that an effective sacrificial donor must be irreversibly oxidized into inert molecules [3]. This prevents side reactions

• various acids [49]. This system is completely metal-free and uses one photocatalyst rather than separate sensitizer and catalyst species. However, the electron source for the reductions was a thiolate sacrificial donor and not water. Thiolates are used as redox mediators in other systems such as dye

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• zinc porphyrin sensitizer with a H2-evolving cobalt diimine dioxime catalyst. First, the Zn porphyrin 88b was coupled with the copper diiminedioxime complex 89 via the CuAAC click reaction to give porphyrin complex 90 in 74% yield (Scheme 18). Furthermore, a stable Co(III) complex was obtained by the

• metal exchange reaction of porphyrin 90 with excess CoCl2·6H2O in an acetone/THF (1:1) mixture. The results of the photophysical investigations demonstrated that these dyads exhibit adequate electronic interactions between the sensitizer and catalyst in the excited state. In this study, NiO films were

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• rim of the CDs could also be optimized, leading to the conformational fixation of both the sensitizer and the guest within the chiral cavity and producing the high ee values. For 8c and 8d, the self-inclusion of the aromatic chromophore might be interrupted, resulting in the long distance from the

• . Adapted with permission from [19], Copyright 2009 American Chemical Society. The sensitizer 5 was prepared by a flavin–zinc(II)–cyclen complex for the photooxidation of benzyl alcohol. Figure 4 reproduced from [20]. Copyright © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim. Used with permission from R

• . Cibulka et al., Catalytic Photooxidation of 4‐Methoxybenzyl Alcohol with a Flavin–Zinc(II)‐Cyclen Complex, Chemistry – A European Journal, John Wiley and Sons. Enantiodifferentiating Z–E photoisomerization of cyclooctene sensitized by a chiral sensitizer as the host. Adapted with permission from [24

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• efficiently via a triplet-mediated pathway without use of any external sensitizer. Similar to bicyclic systems, some of the tricyclic system like 1h yielded 1,2-AS product 2h under similar reaction conditions [16]. Initially we envisaged two mechanistic pathways: the oxa-di-π-methane (ODPM) path

• -dependent absorption spectra [13]. Also no external sensitizer was needed for these transformations. So an efficient intersystem crossing (ISC) may be involved in such systems to reach to the triplet state. A further fascinating aspect is that the two competitive pathways viz. 1,2-AS and photoindiuced 1,5

• -requirement of any sensitizer in the process indicates that the reaction presumably proceeds via a triplet-mediated pathway. Moreover, the non-appearence of any 1,2-AS product signifies that the β,γ-enone part is inactive. On the other hand (cis)-dibenzoylalkene like α,β-enone part of such multichromophoric

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

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• converted the aryl and alkyl α-keto acids 17.1 to the 3-acylindoles 17.3 using rose bengal (OD15) as a photocatalyst under aerobic conditions. Mechanistic studies suggest that rose bengal (OD15) acts as an energy transfer sensitizer generating singlet oxygen. The authors proposed that the latter would be

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• facilitated to shift the absorption between 750–1000 nm. This enabled their use in applications with light sources emitting in the near-infrared (NIR) region selected from high power LEDs or lasers with line-shaped focus. The absorbers considered were discussed regarding their function as sensitizer for

• processes requesting heat to initiate either chemical (activated reactions) or physical (melting, evaporation) events. Keywords: chemistry 4.0; cyanine; near infrared; photopolymer; polymer synthesis; sensitizer; Introduction Cyanines have received in the class of polymethines big attention within the

• in a given application which can be either a sensitizer, initiator, staining, activator or a filter material just to name a few possible examples. Unfortunately, literature often does not clearly distinguish between their functionality. Besides cyanines, there were made huge efforts to synthesize

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• oxime carbamates 8–13 might be excited at their triplet states via triplet state energy transfer from acetophenone as a sensitizer, dissociate to their iminyl/carbamoyloxyl and subsequent anilinyl radicals, attack DNA and cleave it (Figure 7). As shown in Figure 8 none of the compounds show any cleavage

• fluorenone (FL) and carotene (CR), which exhibit low triplet state energy (≈50 and 19 kcal/mol, respectively) [83] and may, acting as a triplet quencher, accept energy transfer from oxime carbamate 12, having now the latter compound as the sensitizer. In this case we expect to have decrease or elimination of

• sensitizer, which transferred its energy to inactive oxime carbamates and enabled them to damage DNA. Additionally, the activity of compound 12 was diminished when triplet state quenchers as fluorenone and carotene were introduced into the irradiated DNA mixture. Accordingly, halogenated carbamate

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• of “optically active” ions: a sensitizer (often ytterbium) and an emitter (“activator”) such as thulium (UV and blue emissions), holmium (red) or erbium (mostly green). In this solid solution, energy collected by ytterbium at 976 nm is transferred to the less abundant emitting ions. Thanks to

• two-photon excitation that requires very high local power density, the upconversion process is based on multiple, noncoherent, “single photon” successive absorptions. As the molar extinction coefficient of the sensitizer ytterbium is weak (ca. 3 mol L−1 cm−1), the exciting beam is moderately

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• ; sensitizer; transient absorption spectroscopy; Introduction Photochromism, which is defined as the reversible transformation of a chemical species between two structural isomers by light, has been extensively studied over decades [1][2][3][4]. Recently, visible-light sensitized photochromic materials have

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• species – a photocatalyst. If the interacting mode between the sensitizer and the reactant is via charge transfer, it is named photoredox catalysis. This research field has been established over the past decade [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In principle, it is a

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• of a triplet sensitizer, mediate the spin change (which otherwise is forbidden) and accelerate the cycloreversion. Substitution in the 2 and 3 positions shifts the bathochromic absorption to 375 nm which is in agreement with similar systems [8]. Furthermore, the cyano and ethynyl groups provide a

Functional panchromatic BODIPY dyes with near-infrared absorption: design, synthesis, characterization and use in dye-sensitized solar cells

• Quentin Huaulmé,
• Cyril Aumaitre,
• Outi Vilhelmiina Kontkanen,
• David Beljonne,
• Alexandra Sutter,
• Gilles Ulrich,
• Renaud Demadrille and
• Nicolas Leclerc

Beilstein J. Org. Chem. 2019, 15, 1758–1768, doi:10.3762/bjoc.15.169

• sensitizer has to display high molar absorption coefficients, ideally along the entire visible range. Additionally, it must display appropriate positioning of frontier molecular orbitals (highest occupied molecular orbital/lowest unoccupied molecular orbital, HOMO/LUMO) energy levels with respect to the

• [27]. Furthermore, it has been reported that introduction of hydrophobic alkyl chains on a sensitizer is a way to improve the open-circuit voltage (Voc), by reducing the electronic recombination rate at the electrolyte/semi-conducting oxide interface [28]. To probe the validity of this concept for a

• TiO2, sensitization has been performed on 2 µm thick TiO2 mesoporous layer (see Figure 5b and c). To prevent dye aggregation on the surface of the semi-conducting oxide, and to mimic the real conditions of use in solar cells, chenodeoxycholic acid (CDCA) was employed as co-sensitizer and hence added to

Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds

• Liudmila L. Rodina,
• Xenia V. Azarova,
• Jury J. Medvedev,
• Dmitrij V. Semenok and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2018, 14, 2250–2258, doi:10.3762/bjoc.14.200

• in THF solutions with added sensitizers (Table 1). In the case of diazodiketone 1а the only isolated product was hydrazone 2а with 33–49% yields (Table 1, entries 1–3). Increasing the amount of sensitizer (up to 10:1) enhanced the yield of hydrazone 2а by 1/2 while reducing the irradiation time by 50

• yields of hydrazones 2, an effort was undertaken to optimize the photochemical reaction conditions by varying the wavelength of irradiation, sensitizer, as well as the ratio of sensitizer/diazodiketone 1b (Table 1, entries 4–9). As can be seen from the data in Table 1 the most effective sensitizer for

• ketone, a complex product mixture was obtained, from which it was impossible to isolate pure compounds. When varying the ratio of sensitizer/diazodiketone 1b, the best result was obtained with a 10-fold excess of benzophenone (Table 1, entry 7; 71% yield). Application of a 4-fold excess of this

Superstructures with cyclodextrins: Chemistry and applications IV

• Gerhard Wenz

Beilstein J. Org. Chem. 2017, 13, 2157–2159, doi:10.3762/bjoc.13.215

• , buckminsterfullerene C60 was covalently linked to two γ-CD rings [14]. This conjugate is highly soluble in water because it forms a sandwich-like self-complex, which makes it particularly useful as a sensitizer for singlet oxygen 1O2 generation [14]. Amphiphilic CD derivatives with oligoethylene oxide side chains form

• nanoparticles with the sensitizer Zn-phthalocyanine and the antineoplastic drug docetaxel. These materials might be applicable for dual cancer therapy [15]. Another self-assembled CD nanocarrier for the photoreactive dye squaraine that is useful for photodynamic therapy is described in this Thematic Series [16