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

• crown ether. The authors reported switchable tweezers bearing metalloporphyrin arms that can be switched by the addition of K+ and Na+ cations. The cation brings the porphyrins together and causes some dynamic fluorescence quenching from the iodine counter anion. The authors attributed the more

• constant is higher for the second complexation than the first. The authors later reported a similar system with triazole linkages between the porphyrin and the indoles that act as binding sites for the metal (square planar complex) [76]. These tweezers present a fluorescence quenching upon copper(I

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• a reductive quenching mechanism. However, since the overall transformation is redox-neutral, no stoichiometric reductant was employed. Instead, fluorescence-quenching studies suggested that the reductive quenching of the iridium excited state (*IrIII) was taking place "off-cycle" via oxidation of

• photosensitizer in an energy-transfer (EnT) mechanism. This proposal was supported by fluorescence quenching measurements, as well as the direct excitation of 44 by UV irradiation, resulting in the formation of 45 in a 45% yield. According to this hypothesis, NHPI ester 44 would adopt a favorable conformation (46

Synthesis of the 3’-O-sulfated TF antigen with a TEG-N₃ linker for glycodendrimersomes preparation to study lectin binding

• Mark Reihill,
• Hanyue Ma,
• Dennis Bengtsson and
• Stefan Oscarson

Beilstein J. Org. Chem. 2024, 20, 173–180, doi:10.3762/bjoc.20.17

• silica gel 60 F254. Visualisation was performed with UV-light (254 nm) fluorescence quenching, and/or by staining with an 8% H2SO4 dip (stock solution: 8 mL conc. H2SO4, 92 mL EtOH), ninhydrin dip (stock solution: 0.3 g ninhydrin, 3 mL AcOH, 100 mL EtOH) and/or ceric ammonium molybdate dip (stock

Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[c]quinolizinium ions

• Julika Schlosser,
• Olga Fedorova,
• Yuri Fedorov and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 101–117, doi:10.3762/bjoc.20.11

• efficient fluorescence quenching (Figure 5), which is commonly observed with this class of cationic ligands [3][70], mainly as a result of a photoinduced electron transfer from the excited, DNA-bound ligand with the DNA bases [71]. The binding isotherms obtained from the titration data were used to

Tying a knot between crown ethers and porphyrins

• Maksym Matviyishyn and
• Bartosz Szyszko

Beilstein J. Org. Chem. 2023, 19, 1630–1650, doi:10.3762/bjoc.19.120

• alkylammonium guests. The binding constants Ka in CHCl3/MeOH 9:1 determined for 9-Zn complexes with [NH3(CH2)NH2]+, [NH3(CH2)2NH3]2+, [NH3(CH2)3NH3]2+, and [NH3CH2CH3]+ equal to 8.3·103, 6.2·103, 8.7·103, and 7.7·102 M−1, respectively, were reported. Based on the fluorescence quenching experiments the formation

The effect of dark states on the intersystem crossing and thermally activated delayed fluorescence of naphthalimide-phenothiazine dyads

• Liyuan Cao,
• Xi Liu,
• Xue Zhang,
• Jianzhang Zhao,
• Fabiao Yu and
• Yan Wan

Beilstein J. Org. Chem. 2023, 19, 1028–1046, doi:10.3762/bjoc.19.79

• infer that the emissive S1 state has a substantial CS character [56]. Thus, the assignment of the emissive S1 state to a CS state is reasonable. Upon oxidation of the PTZ moiety, the degree of fluorescence quenching in polar solvents became less significant than that of the compounds with a native PTZ

A fluorescent probe for detection of Hg²⁺ ions constructed by tetramethyl cucurbit[6]uril and 1,2-bis(4-pyridyl)ethene

• Xiaoqian Chen,
• Naqin Yang,
• Yue Ma,
• Xinan Yang and
• Peihua Ma

Beilstein J. Org. Chem. 2023, 19, 864–872, doi:10.3762/bjoc.19.63

• + ions [34]. Because of the synergistic combination of Q[8], SQ2 and Hg2+ ions, it shows fluorescence quenching. Cong's group found that Q[7] can encapsulate the benzimidazole part of N-(2-benzimidazolylmethyl)-N,N-bis(2-pyridylmethyl)amine cation (BIBPA+) to construct a host–guest fluorescent probe. The

Photocatalytic sequential C–H functionalization expediting acetoxymalonylation of imidazo heterocycles

• Deepak Singh,
• Shyamal Pramanik and
• Soumitra Maity

Beilstein J. Org. Chem. 2023, 19, 666–673, doi:10.3762/bjoc.19.48

• ]. Finally, the reaction of 5 with benzoic acid and zinc acetate (in a 1:1 ratio) under standard reaction protocol resulted in the competitive formation of products 4a and 10 (Scheme 3E), indicating the susceptibility of other acids towards this method. These results, along with the Stern–Volmer fluorescence

• quenching study (Scheme 3F), expressed that the photoredox reaction started with the reductive generation of a malonyl radical from bromomalonate by interaction with the photocatalyst. Analyzing all the observations from the above mechanistic studies, we propose a plausible mechanism involving sequential

Phenanthridine–pyrene conjugates as fluorescent probes for DNA/RNA and an inactive mutant of dipeptidyl peptidase enzyme

• Josipa Matić,
• Tana Tandarić,
• Marijana Radić Stojković,
• Filip Šupljika,
• Zrinka Karačić,
• Ana Tomašić Paić,
• Lucija Horvat,
• Robert Vianello and
• Lidija-Marija Tumir

Beilstein J. Org. Chem. 2023, 19, 550–565, doi:10.3762/bjoc.19.40

• that a higher degree of aromatic surfaces overlapping and cation–π interactions also yield excimer fluorescence quenching [30][32][33]. This conclusion is strongly in line with experimental insight reported here and helps in explaining the observed excimer fluorescence quenching with a decrease in the

• response concerning the excimer band was obtained independently on polynucleotide’s structure and/or base composition. Fluorescence quenching upon binding was similar to the previously published bispyrene–guanidiniocarbonyl compound, which was found to bind along the phosphate backbone of most of examined

• Information File 1). Compound Phen-Py-1 showed high, micromolar/submicromolar affinities for all examined polynucleotides. The binding of Phen-Py-1 to polynucleotides possibly led to the unstacking of intramolecular pyrene–phenanthridine dimer and consequent excimer fluorescence quenching independently of the

Naphthalimide-phenothiazine dyads: effect of conformational flexibility and matching of the energy of the charge-transfer state and the localized triplet excited state on the thermally activated delayed fluorescence

• Kaiyue Ye,
• Liyuan Cao,
• Davita M. E. van Raamsdonk,
• Zhijia Wang,
• Jianzhang Zhao,
• Daniel Escudero and
• Denis Jacquemin

Beilstein J. Org. Chem. 2022, 18, 1435–1453, doi:10.3762/bjoc.18.149

• solvents with higher polarity. This trend is similar to the one previously reported for the NI-N-PTZ analog [20]. We note that the CT emission band of NI-PTZ is slightly red-shifted as compared to that of the previously reported dyad. Upon oxidation of the PTZ moiety, i.e., for NI-PTZ-O, the fluorescence

• quenching in polar solvents is less significant than that of NI-PTZ (Figure 2b), and the CT emission band is blue-shifted as compared to that of NI-N-PTZ [20], a likely consequence of the reduced electron-donating ability of the PTZ moiety. For NI-PTZ2, a solvent polarity-dependent fluorescence band was

Thermally activated delayed fluorescence (TADF) emitters: sensing and boosting spin-flipping by aggregation

• Ashish Kumar Mazumdar,
• Gyana Prakash Nanda,
• Nisha Yadav,
• Upasana Deori,
• Upasha Acharyya,
• Bahadur Sk and
• Pachaiyappan Rajamalli

Beilstein J. Org. Chem. 2022, 18, 1177–1187, doi:10.3762/bjoc.18.122

• twisted intramolecular CT state led to fluorescence quenching in the highly polar water/THF mixture (10–70 vol % water, Figure 3a, c, and e) [34][35][36]. It again started glowing when the water fraction was increased beyond 80 vol % (Figure 3a, c, and e). The formation of molecular aggregates in >80 vol

•  2). Therefore, it is evident that the aggregation helped to suppress the fluorescence quenching as well as to boost the DF by reducing the ΔEST in BPy-pTC. At the same time, the significant enhancement of the PF lifetime was due to the molecular rigidification and restriction of D–A rotation in BPy

Synthesis of a novel aminobenzene-containing hemicucurbituril and its fluorescence spectral properties with ions

• Qingkai Zeng,
• Qiumeng Long,
• Jihong Lu,
• Li Wang,
• Yuting You,
• Xiaoting Yuan,
• Qianjun Zhang,
• Qingmei Ge,
• Hang Cong and
• Mao Liu

Beilstein J. Org. Chem. 2021, 17, 2840–2847, doi:10.3762/bjoc.17.195

• +, and Mn2+ (nitrate salts were used as cation sources) in DMF resulted in different degrees of quenching of the fluorescence emission of host 4. The results are collected in Figure 3 as the corresponding fluorescence quenching efficiency which was quantified using the equation ΔI = (I0 − I), where I is

• ) of 4 (2.5 × 10−5 M) in the presence of 10 equivalents of Ag+, Co2+, Cr3+, Cu2+, Fe3+, Mn2+, Na+, NH4+ (2.5 × 10−4 M) in DMF at 298 K. Column diagram of fluorescence quenching efficiency of 4 (2.5 × 10−5 M) in the presence of 10 equivalents of Ag+, Cr3+, Ni2+, Cu2+, Fe3+, Co2+, Na+, NH4+ and Mn2+ (2.5

• −1. In another perspective, the presence of the coordination of selected anions to the macrocyclic sensor enhanced the fluorescence emission in various degree, extremely contrary to the classic heavy-atom effect caused by a heavy atom. In general, this macrocyclic sensor showed high fluorescence

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

• Premansh Dudhe,
• Mena Asha Krishnan,
• Kratika Yadav,
• Diptendu Roy,
• Krishnan Venkatasubbaiah,
• Biswarup Pathak and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2021, 17, 1453–1463, doi:10.3762/bjoc.17.101

• moderately polar dichloromethane and then highly polar DMSO (Table 2, Figure 3). The fluorescence quenching of 3ac in methanol is attributed to the partial protonation of the carboline unit's nitrogen atoms facilitated by polar-protic solvents [33]. The fluorescence lifetimes were measured by time-correlated

The fluorescence of a mercury probe based on osthol

• Guangyan Luo,
• Zhishu Zeng,
• Lin Zhang,
• Zhu Tao and
• Qianjun Zhang

Beilstein J. Org. Chem. 2021, 17, 22–27, doi:10.3762/bjoc.17.3

• , and high sensitivity [10][11][12]. In recent years, many fluorescent molecular probes have been reported. Because Hg2+ has a very strong quenching effect on fluorescence, most of the fluorescent molecular Hg2+ probes are of the fluorescence-quenching type and are easily interfered with by other

• +, a coexisting ion experiment was carried out (Figure 2) [24]. The fluorescence intensity was measured by adding 1.2 × 10−4 mol∙L−1 of various metal ions to the OST–Hg2+ (c = 3.0 × 10−5 mol∙L−1) probe system. It is found that Fe3+ had a certain fluorescence quenching effect on the system due to the

• paramagnetism [25], but the fluorescence quenching effect was not enough to affect the recognition of mercury ions by the probe, and the presence of other coexisting metal ions did not affect the fluorescence spectrum change of the OST–Hg2+ system. Drawing the standard curve [26] Figure 3A shows the

Selective recognition of ATP by multivalent nano-assemblies of bisimidazolium amphiphiles through “turn-on” fluorescence response

• Rakesh Biswas,
• Surya Ghosh,
• Shubhra Kanti Bhaumik and
• Supratim Banerjee

Beilstein J. Org. Chem. 2020, 16, 2728–2738, doi:10.3762/bjoc.16.223

• of anthracene tagged imidazolium receptors responded to ATP through an amplified fluorescence quenching [60]. Based on these results, we wanted to develop similar self-assembled systems which would show a “turn-on” response in the presence of ATP or other phosphate analytes. The current design of

Naphthalene diimide–amino acid conjugates as novel fluorimetric and CD probes for differentiation between ds-DNA and ds-RNA

• Annike Weißenstein,
• Myroslav O. Vysotsky,
• Ivo Piantanida and
• Frank Würthner

Beilstein J. Org. Chem. 2020, 16, 2032–2045, doi:10.3762/bjoc.16.170

• stronger quenching for GC-DNA and the weaker for AT(U)-polynucleotides (Figure 5a and b). Because guanine is the most electron-rich nucleobase, this behaviour points at a fluorescence quenching mechanism by charge transfer from the electron-rich purine bases to the electron-poor NDI molecular probes

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• fluorescence quenching studies, UV–vis spectroscopy experiments, calculation of the quantum yield, a cutoff experiment below 400 nm, GC–MS analysis, and NMR spectroscopic mechanistic experiments. They also concluded that an energy transfer mechanism could not be possible since the solvent employed affected the

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• hydroxylation of arenes (Scheme 18) [157]. They realized that the photoredox catalyst 8 possesses a great oxidizing ability (Ered vs SCE = 2.72 V) at ambient conditions. The mechanism of the reaction was studied by fluorescence quenching and transient absorption spectroscopy. They observed that the one-electron

Preparation of anthracene-based tetraperimidine hexafluorophosphate and selective recognition of chromium(III) ions

• Qing-Xiang Liu,
• Feng Yang,
• Zhi-Xiang Zhao,
• Shao-Cong Yu and
• Yue Ding

Beilstein J. Org. Chem. 2019, 15, 2847–2855, doi:10.3762/bjoc.15.278

• paramagnetic nature of chromium(III) can cause fluorescence quenching of the fluorophore via the enhancement of spin–orbit coupling [30][31][32][33][34][35]. So far, only a few successful examples of fluorescence enhancement sensors for Cr3+ have been reported [36][37][38][39][40]. Thus, developing new and

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• molecular aggregation in the solid state causes fluorescence quenching [16]. In recent years, we have coined diversity-oriented syntheses of functional chromophores by multicomponent strategies [17][18], opening accesses to substance libraries for systematic studies of structure–property relationships on

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• these dyes such as intramolecular charge-transfer processes and tunable red-shifted emission bands. Generally, the so far investigated borylated arylisoquinoline dyes show principally fluorescence quenching (on-off switching) on the formation of the corresponding fluoroboronate complexes [37]. Herein

• 16–19 on the addition of tetra-n-butylammonium fluoride (Bu4NF) in acetonitrile are depicted. The dyes 16 and 17 show a strong fluorescence quenching of their LW bands, while the SW bands experience a slight increase. However, the situation for the dyes 18 and 19 is dramatically different. Here the

• residue (naphthyl, 4-methoxynaphthyl, pyrenyl, anthryl). This provides some hint that intramolecular charge-transfer phenomena are likely involved. Laser-flash photolysis studies provided insights into the existence of excited triplet states. The addition of fluoride anions led to pronounced fluorescence

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• be responsible for the fluorescence quenching in the Z-form. A comparison of the kinetic traces recorded on the maximum of the excited state absorption band in the three analyzed solvents (Figure 6) demonstrates that the excited state decay time decreases on going from acetonitrile to toluene, and

Targeted photoswitchable imaging of intracellular glutathione by a photochromic glycosheet sensor

• Xianzhi Chai,
• Hai-Hao Han,
• Yi Zang,
• Jia Li,
• Xiao-Peng He,
• Junji Zhang and
• He Tian

Beilstein J. Org. Chem. 2019, 15, 2380–2389, doi:10.3762/bjoc.15.230

• broad and strong absorption makes the 2D MnO2 nanosheets a potential energy acceptor for the fluorophores which are stacked on the nanosheets plane, leading to the fluorescence quenching through FRET mechanism [32][34]. The transmission electron microscopy (TEM) image of the prepared product revealed

• effective FRET between the attached Glyco-DTE and 2D MnO2, which again suggested the close stacking of Glyco-DTE to the nanosheet surface. Aggregation-caused quenching might be another reason for the fluorescence quenching because of the close distance between fluorescence molecules when absorbed on the

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• measurement of the two-photon absorption cross-section, which is a marker of the efficiency of the TPA, displayed a linear increase with the number of fluorophores (Table 1), indicative of an additive behavior. In contrast, the fluorescence properties are only weakly affected. In particular, fluorescence

• quenching is prevented thanks to the design of the fluorophore [42]. It should be noted that the largest dendrimers, in particular generation 4, display very large two-photon absorption cross-sections (σ2 up to 55,900 GM), which are comparable to those measured for the best quantum dots [43]. Thus these