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

• thorough photochemical characterization is essential for efficient light-driven applications. In this article, the mode of action of a polyazahelicene catalyst (Aza-H) was investigated using laser flash photolysis (LFP). The study revealed that the chromophore can function as a singlet-state photoredox

• mechanism of the recently reported sulfonylation/arylation [45][46] reaction using laser flash photolysis (LFP). LFP is a powerful spectroscopic tool in photocatalysis that allows us not only to distinguish between energy and electron transfer but also to detect transient triplet states and radicals

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

• the plausible energy transfer from the local charge-separated (CS) state of the push–pull chromophore (namely N,N-diethylanilino (DEA)•+–TCBD•−) to the singlet excited state of C60 (1C60*). In transient absorption spectral measurements conducted via the femtosecond laser-flash photolysis of compound

• measuring the charge-separation and charge-recombination lifetimes of these molecules by laser-flash photolysis (excitation wavelength = 420 nm) and the resulting electron-transfer rates were plotted. In the measurements in toluene, the lifetimes of the CS states and charge-recombination events differed

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• intrinsic decay rate of *PC1. Since no quenching by 1d or B2pin2 could be observed, the formation of PC1•− can be attributed exclusively to the thermodynamically favored reductive quenching of *PC1 by DBU. Nanosecond laser flash photolysis techniques were employed to directly monitor the back electron

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

• components to be used for Global analysis was estimated by performing a preliminary singular values decomposition (SVD) analysis. All data were chirp-corrected before global fitting. Nanosecond transient absorption spectroscopy The nanosecond transient absorption spectra were measured on a LP920 laser flash

• photolysis spectrometer (Edinburgh Instruments, Ltd., U.K.). The data (kinetic decay traces and the transient difference absorption spectra) were analyzed with the L900 software. All samples were deaerated with N2 for ca. 15 min before measurement and excited with a nanosecond pulsed laser (OPO nanosecond

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

• recorded on a LP920 laser flash photolysis spectrometer (Edinburgh Instruments, Ltd., U.K.). The data (kinetic decay traces and the transient difference absorption spectra) were analyzed with the L900 software. All samples were deaerated with N2 for ca. 15 min in collinear configuration of the pump and

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

• bonds in the presence of photoredox catalyst 8, with a similar mechanism as shown in Figure 22, and the photocatalytic mechanism was elucidated by nanosecond laser flash photolysis (Scheme 24) [168]. Fluorine-18 is an important radioisotope used in the radiopharmaceutical industry (e.g., for drug

• observed that hydroxylation of the fluoro-, chloro-, and bromobenzene derivatives provided low yields. The photocatalytic mechanism for this reaction was inspected by time-resolved transient absorption spectroscopy to detect the triplet–triplet photoredox catalyst spectrum via nanosecond laser flash

• flash photolysis measurements, and the monobrominated product selectivity was controlled by the difference in electron transfer oxidation reactivity of 127 and 126 of electron transfer state of photocatalyst (Me·+ moiety) and also on the radical cations reactivity with Br−. Recently, König’s group

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

• of 0.2–0.4, reaching in some cases values as high as 0.5–0.6. Laser-flash photolysis provided evidence for the existence of excited triplet states. The dyes form fluoroboronate complexes with fluoride anions, leading to the observation of the quenching of the long-wavelength emission band and

• ratiometric response by the build-up of a hypsochromically shifted emission signal. Keywords: anions; dyes; fluorescence; laser-flash photolysis; organoboron; Introduction Boron-containing tri- and tetra-coordinated chromophores have attracted considerable interest due to their often peculiar and highly

• in some cases very close to the resolution limit of our time-correlated single-photon-counting setup. The LW emission showed considerably longer lifetimes in the 3–6 ns range. The photophysical behavior of the dyes is tentatively summarized in Scheme 4. Laser-flash photolysis The photophysical

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

• emission spectra was measured to separate the fluorescence and phosphorescence. The shutter was controlled by LabVIEW. Nanosecond transient absorption measurements The laser flash photolysis experiments were carried out with a TSP-2000 time resolved spectrophotometer system (Unisoku Co., Ltd.). A 10 Hz Q

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

• Amrita Das,
• Mitasree Maity,
• Simon Malcherek,
• Burkhard König and
• Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

• (1,3,5-TMB•+) is formed indeed during the quenching process of the catalyst by 1,3,5-TMB (Scheme 5) ns-time-resolved transient absorption spectroscopy was used [50]. To allow for a decomposition of the multicomponent spectra we conducted laser flash photolysis (LFP) experiments on the single components

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• , mutagenous properties were also shown. Freccero et al. examined the photogeneration by laser flash photolysis and reactivity of naphthoquinone methides as well as their activity as purine selective DNA alkylating agents [93]. Farrell et al. studied the mechanism of the cytotoxic action of naphthoquinone

• phenolic Mannich bases bearing functional groups that are suitable for cross-linking DNA; therefore, their antitumor effects could also be confirmed [96]. The formation of o-QMs and their biological properties were also illustrated by kinetic studies. Rokita et al. using laser flash photolysis showed that

Biradical vs singlet oxygen photogeneration in suprofen–cholesterol systems

• Fabrizio Palumbo,
• Francisco Bosca,
• Isabel M. Morera,
• Inmaculada Andreu and
• Miguel A. Miranda

Beilstein J. Org. Chem. 2016, 12, 1196–1202, doi:10.3762/bjoc.12.115

• with reduction of the BZT chromophore. Dyads 1 and 2 were efficiently photolyzed under anaerobic conditions, whereas 3 was markedly unreactive. Interestingly, 2 was significantly more photoreactive than 1 indicating a clear stereodifferentiation in the photochemical behavior. Laser flash photolysis

• ammonium molybdate reagent. The residues were purified through silica gel 60 (0.063–0.2 mm). Exact mass was obtained by Waters ACQUITY™ XevoQToF spectrometer. Laser flash photolysis (LFP) measurements As described in [17], a pulsed Nd:YAG laser was used for the excitation at 355 nm. The single pulses were

Photo, thermal and chemical degradation of riboflavin

• Muhammad Ali Sheraz,
• Sadia Hafeez Kazi,
• Sofia Ahmed,
• Zubair Anwar and
• Iqbal Ahmad

Beilstein J. Org. Chem. 2014, 10, 1999–2012, doi:10.3762/bjoc.10.208

• it was found to be higher in D2O (66%) in comparison to that of distilled water (40%) [57]. The effects of various solvents on the rates of flavin redox reactions have been investigated using laser flash photolysis [50]. The effect of aqueous and organic solvents on the photolysis of FMF has been

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

• Christian Ley,
• Julien Christmann,
• Ahmad Ibrahim,
• Luciano H. Di Stefano and
• Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

• different rate constants involved in the proposed mechanism were measured by time resolved spectroscopies (laser flash photolysis for triplet excited states and time correlated single photon counting for excited singlet states). The experimental quenching rate constants and their corresponding ΔGET are

• given in Table 2. As kred and kox were not measurable, a value of 2·103 M−1·s−1 was taken to perform the computations. This is justified by the fact that the radical recombination in the type II systems observed by laser flash photolysis occurs in the ms timescale. The last row of Table 2 contains the

• cell. Laser flash photolysis experiments (LFP) were carried out exciting at 532 nm with a nanosecond Nd-YAG laser (Powerlite 9010, Continuum), operating at 10 Hz. The transient absorption analysis system (LP900, Edinburgh Instruments) uses a 450 W pulsed Xe arc lamp, a Czerny–Turner monochromator, a

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

• Jacques Lalevée,
• Sofia Telitel,
• Pu Xiao,
• Marc Lepeltier,
• Frédéric Dumur,
• Fabrice Morlet-Savary,
• Didier Gigmes and
• Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

• -trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments. Keywords: LEDs; photoinitiators; photopolymerization; photoredox catalysis; Introduction Photoredox catalysis is now well-known and largely used in organic synthesis, especially in the development

• panchromatic behavior in the 400–650 nm range. The PIC/Ph2I+/NVK system The photochemical properties of Ir(piq)2(tmd) A triplet-state lifetime of 1.1 μs has been determined for Ir(piq)2(tmd) by laser flash photolysis experiments. A relatively similar lifetime (1.3 μs) was previously measured for 3Ir(ppy)3 [68

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• to radical pairs by laser flash photolysis. Without further action on the part of the experimenter, the radical pair mechanism then creates opposite polarizations in the geminate products, i.e., in the starting materials A and D regenerated by reverse electron transfer, and in the escaping free

Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

• Jianhuai Ye,
• Yoshihisa Fujiwara and
• Manabu Abe

Beilstein J. Org. Chem. 2013, 9, 925–933, doi:10.3762/bjoc.9.106

• entropy effect were found to play crucial roles in increasing the lifetime. Keywords: laser flash photolysis; lifetime; singlet diradicals (biradicals); substituent effect; π-single bond; Introduction Localized singlet diradicals are key intermediates in processes involving the homolytic bond-cleavage

• . Detection of singlet diradicals DRc–g. The detection of singlet diradicals DRc–g was examined by the photochemical denitrogenation of azoalkanes AZc–g in a glassy matrix of 2-methyltetrahydrofurane (MTHF) at 80 K, [AZ] ≈ 4 × 10−3 mol/L, and by the laser flash photolysis experiments of AZc–g at room

• ]. Lifetime of singlet diradicals DRc–g and activation parameters for the ring-closing reaction. The decay traces of the intermediary singlet diradicals DRc–g at 293–333 K were measured in a benzene solution by the laser flash photolysis technique (λexc = 355 nm). The lifetime (τ = 1/k) was determined by the

New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

• Sofia Telitel,
• Frédéric Dumur,
• Thomas Faury,
• Bernadette Graff,
• Mohamad-Ali Tehfe,
• Didier Gigmes,
• Jean-Pierre Fouassier and
• Jacques Lalevée

Beilstein J. Org. Chem. 2013, 9, 877–890, doi:10.3762/bjoc.9.101

• photocatalysts. Successful results in terms of rates of polymerization and final conversions were obtained. The strong MO coupling between the six different cores and the pyrene moiety was studied by DFT calculations. The different chemical intermediates are characterized by ESR and laser flash photolysis

• halide for FRP. The monomers investigated are given in Scheme 4. The mechanisms are analyzed by electron spin resonance (ESR), steady-state photolysis, fluorescence and laser flash photolysis (LFP). The ability of Co_Pys to behave as new organophotocatalysts is also discussed. Results and Discussion

• to radical polymerization. Laser flash photolysis Upon laser excitation of Py_3 at 355 nm, a triplet state T1 characterized by a maximum absorption at ~420 nm and a rather long lifetime is formed (t > 4 μs) (Figure S2 in Supporting Information File 1). This T1 state is similar to that of Py_1 [31

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

• Maurizio Fagnoni,
• Stefano Protti,
• Davide Ravelli and
• Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

• the presence of a variety of donors (D–X, step a). In all of the above cases, the generated radical anion (A–Y•−) is a persistent species easily detected by laser flash photolysis. This approach applies to a variety of donors, including amines [12][13], carboxylic acids or their derivatives [14][15

• further tertiary amines, iPr3N causes a somewhat slower accumulation (the conformation of the radical cation is known to be less favorable for deprotonation) [48][49][50], and DABCO (for which deprotonation is impossible [51][52]) causes no detectable formation of TCB•−. Indeed, previous laser flash

• photolysis experiments had shown that DABCO formed the TCB radical anion on the nanosecond time scale just as the other tertiary amines [53]. However, no reaction able to eliminate radical cations was viable in this case, and thus BET predominated (path a' in Scheme 2 and path α in Figure 4). Irreversible

New reactive intermediates in organic chemistry

• Götz Bucher

Beilstein J. Org. Chem. 2013, 9, 613–614, doi:10.3762/bjoc.9.67

• and hence can be studied for an extended period of time; or laser flash photolysis, where the reactive intermediate is generated by a very short pulse of laser light, and can be investigated in real time; or specialised mass-spectrometric techniques such as ion cyclotron resonance MS. Due to the

A chemist and biologist talk to each other about caged neurotransmitters

• Graham C.R. Ellis-Davies

Beilstein J. Org. Chem. 2013, 9, 64–73, doi:10.3762/bjoc.9.8

• most purposes. I have been confused by some reports of “rates of reactions” being given as a time course for steady-state photolysis over many seconds or minutes [45], whereas other reports show rates from laser flash photolysis [3][61]. Can you help clarify this? Chemist: Only the latter should be

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• corresponding N parameters – LFP = laser flash photolysis. Comparison of the electrophilicities of cinnamaldehyde-derived iminium ions 3a–3i. Nucleophiles used in iminium activated reactions [35][42][44][45][46][47][48][49][50][51][52]. Counterion effects in electrophilic reactions of iminium ions 3a-X (at 20

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• )azobenzene (10) revealed very different behaviours. While the azoderivative 4 exhibits a very slow thermal isomerisation, which can be nicely followed by conventional time-resolved absorption spectroscopy, the thermal back reaction of azophenol 10 must be determined by the laser flash-photolysis technique

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• photophysical and photochemical properties of N-phthaloylvaline methyl ester (1) have been studied by nanosecond laser flash photolysis (λexc = 248 or 308 nm) [5]. The quantum yield of fluorescence is low (ФF = 10−2), whereas that of phosphorescence at −196 °C is large (0.5). The triplet properties of 1 at room

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• -scale from −1 ps to 1 ps and the logarithmic scale thereafter. a) Two-dimensional overview plot of the transient absorbance changes in false colour coding. a.u. = arbitrary units. b) Temporal behaviour of the absorbance changes at a detection wavelength of 470 nm. c) Results from laser-flash photolysis