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Photocatalytic nucleophilic addition of alcohols to styrenes in Markovnikov and anti-Markovnikov orientation
摘要： The nucleophilic addition of methanol and other alcohols to 1,1-diphenylethylene (1) and styrene (6) into the Markovnikov- and anti-Markovnikov-type products was selectively achieved with 1-(N,N-dimethylamino)pyrene (Py) and 1,7-dicyanoperylene-3,4:9,10-tetracarboxylic acid bisimide (PDI) as photoredox catalysts. The regioselectivity was controlled by the photocatalyst. For the reductive mode towards the Markovnikov-type regioselectivity, Py was applied as photocatalyst and triethylamine as electron shuttle. This approach was also used for intramolecular additions. For the oxidative mode towards the anti-Markovnikov-type regioselectivety, PDI was applied together with Ph–SH as additive. Photocatalytic additions of a variety of alcohols gave the corres- ponding products in good to excellent yields. The proposed photocatalytic electron transfer mechanism was supported by detection of the PDI radical anion as key intermediate and by comparison of two intramolecular reactions with different electron density. Representative mesoflow reactor experiments allowed to significantly shorten the irradiation times and to use sunlight as “green” light source.
关键词： perylene bisimide,photochemistry,pyrene,photocatalysis,electron transfer
更新于2025-09-23 15:21:21
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UV-Induced Crosslinking of Poly[2-(2’-Norbornenyl)-2-Oxazoline]s
摘要： A 2-oxazoline monomer bearing a norbornenyl functionality in the side-chain was prepared from the reaction of 5-norbornene-2-carbonitrile and 2-ethanol amine. This monomer could be successfully polymerized using a 2-oxazolinium-based macroinitiator that was in-situ generated from the methyl cation-initiated oligomerization of 2-ethyl-2-oxazoline. This polymer could be subjected to polymeranalogous reactions involving the alkene groups of the norbornenyl side-chains: A proof-of-concept was established by utilizing the polymers in photoresists that were crosslinked by thiol-ene reactions involving bisfunctional thiols. Photoinitiators for the UV-induced thiol-ene reaction were required in catalytic amounts only. After development, the resists exhibited reproduction of the geometric patterns with a resolution of 30 μm.
关键词： cationic polymerization,polymer photochemistry,microwave-assisted polymerization,poly(2-oxazoline)s,photoresist,thiol-ene reaction
更新于2025-09-23 15:21:21
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Unlocking a diazirine long-lived nuclear singlet state via photochemistry: NMR detection and lifetime of an unstabilized diazo-compound
摘要： Diazirines are important for photoaffinity labelling and their photoisomerization is relatively well known. This work shows how hyperpolarized NMR spectroscopy can be used to characterise an unstable diazo-compound formed via photoisomerization of a 15N2-labelled silyl-ether substituted diazirine. This diazirine is prepared in a nuclear spin singlet state via catalytic transfer of spin order from para-hydrogen. The active hyperpolarization catalyst is characterised to provide insight into the mechanism. The photochemical isomerisation of the diazirine into the diazo-analogue allows the NMR invisible nuclear singlet state of the parent compound to be probed. The identity of the diazo-species is confirmed by trapping with N-phenyl maleimide via a cycloaddition reaction to afford bicyclic pyrazolines that also show singlet state character. The presence of singlet states in the diazirine and the diazo-compound are validated by comparison of experimental nutation behaviour with theoretical simulation. The magnetic state lifetime of the diazo-compound is determined as 12 ± 1 s in CD3OD solution at room temperature whereas its chemical lifetime is measured as 100 ± 5 s by related hyperpolarized NMR studies. Indirect evidence for the generation of the photoproduct para-N2 is presented.
关键词： SABRE-SHEATH,photochemistry,para-hydrogen,diazirine,photoisomerization,nuclear spin singlet state,diazo-compound,hyperpolarized NMR spectroscopy
更新于2025-09-23 15:21:21
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Photoregeneration of Biomimetic Nicotinamide Adenine Dinucleotide Analogues via a Dye-Sensitized Approach
摘要： Two-step photochemical reduction of an acridinium-based cation 2O+ to the corresponding anion 2O? was investigated using a dye-sensitized approach involving 2O+?COOH attached to the surface of a wide-bandgap semiconductor, p-NiO. The cation 2O+ and corresponding one-electron reduced radical form, 2O? were synthesized and characterized using steady-state UV/vis and electron paramagnectic resonance spectroscopy. The thermodynamics for the photoinduced hole injection from 2O+ and 2O? were evaluated and found to be favorable. Subsequent femtosecond transient absorption spectroscopy was utilized to evaluate the photoinduced hole injection into NiO, starting from 2O+?COOH/NiO and 2O??COOH/NiO samples. The excitation of 2O+?COOH at 620 nm initiated fast (2.8 ps) hole injection into NiO. However, 90% of the charge-separated population recombined within ～40 ps, while ～10% of the charge-separated population exhibited lifetimes longer than the time scale of our instrument (1.6 ns). In the case of 2O??COOH/NiO, the light absorption occurs predominantly by NiO (2O??COOH absorbs at 310 nm) and is associated with the electron transfer from the conduction band of NiO to the radical. The charge-separated state in this case appears to be long-lived, based on the slow (ns) growth of the trapped carriers formed on the NiO surface. The results of this work indicate that the photochemical reduction of 2O+ to the corresponding hydride form (2OH) can be achieved, opening the possibility of using such a dye-sensitized approach for regeneration of nicotinamide adenine dinucleotide analogues in enzymatic and chemical catalysis.
关键词： multiple charge accumulation,stable radical,NADH,photochemistry,NiO,dye sensitization
更新于2025-09-23 15:21:21
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The Light Triggered Dissolution of Gold Wires using Potassium Ferrocyanide Solutions Enables Cumulative Illumination Sensing
摘要： Electronic systems with on-demand dissolution or destruction capabilities offer unusual opportunities in hardware-oriented security devices, advanced military spying and controlled biological treatment. Here, the dissolution chemistry of gold, generally known as inert metal, in potassium ferricyanide and potassium ferrocyanide solutions has been investigated upon light exposure. While a pure aqueous solution of potassium ferricyanide – K3[Fe(CN)6] does not dissolve gold, an aqueous solution of potassium ferrocyanide – K4[Fe(CN)6] irradiated with ambient light is able to completely dissolve a gold electrode within several minutes. Photo activation and dissolution kinetics were assessed at different initial pH values, light irradiation intensities and ferrocyanide concentrations. Addition of small amounts of the heavy metal thallium (260 ppb) also provides tunability of the dissolution kinetics. An investigation of the involved chemical and physical processes of photochemistry, cyanide diffusion and surface reaction results in an understanding of the rate limiting steps, and yields an overall transformation of irradiated light energy to dissolved gold of 2.6 %. A potential application of this novel gold dissolution method as a cumulative light sensor is demonstrated and discussed.
关键词： sensor,conductors,photochemistry,cyanide,devices,diffusion limitation
更新于2025-09-23 15:21:01
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Spatially resolved covalent functionalization patterns on graphene
摘要： Spatially resolved functionalization of 2–D materials is highly demanded but very challenging to achieve. The chemical patterning is typically tackled by preventing contact between the reagent and material, with various accompanying challenges. Photochemical transformation on the other hand inherently provides remote high spatiotemporal resolution using the cleanest reagent – a photon. Here, we combine two competing reactions on a graphene substrate to create functionalization patterns on a micrometre scale via the Mitsunobu reaction. The mild reaction conditions allow introduction of covalently dynamic linkages, which can serve as reversible labels for surface- or graphene-enhanced Raman spectroscopy characterization of the patterns prepared. The proposed methodology thus provides a pathway for local introduction of arbitrary functional groups on graphene.
关键词： patterned functionalization,Mitsunobu reaction,photochemistry,graphene,Raman spectroscopy
更新于2025-09-23 15:21:01
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A Pentacene-based Nanotube Displaying Enriched Electro/Photochemical Activities
摘要： We report the first synthesis of a pentacene-based nanotube displaying a tubular conformation in solution. The product possesses a triangular prismatic structure with three pentacene chromophores connected by a rigid, triangular backbone. Steady-state and time-resolved spectroscopic analyses revealed that the nanotube exhibits enriched electro/photochemical activities due to the close proximity of the three pentacene chromophores, which allows for efficient intramolecular singlet fission and long-lived triplet excitons.
关键词： photochemistry,pentacene,singlet fission,nanotube,triplet excitons,electrochemistry
更新于2025-09-23 15:21:01
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Scaling-up UV-mediated Intramolecular-Photo-Dehydro-Diels-Alder reactions using a Homemade High-Performance Annular Continuous-Flow Reactor
摘要： In this communication, we present a self-made annular continuous-flow reactor, which can be used in the UV/Vis-range in an internal numbering-up manner. As a model reaction, we chose a powerful and batch scale-limited benzoannelation method, which is an intramolecular Photo-Dehydro-Diels-Alder (IMPDDA) reaction. The scaling-up potential of this particular photochemical benchmark reaction towards the preparation of macrocylic (1,7)naphthalenophanes by variation of selected flow parameters is presented.
关键词： flow photochemistry,scaling-up,photocycloaddition,Photo-Dehydro-Diels-Alder reaction
更新于2025-09-23 15:21:01
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Application of Nanostructured Tungsten Fabricated by Helium Plasma Irradiation for Photoinduced Decolorization of Methylene Blue
摘要： The dendritic nanostructure was fabricated on a surface of tungsten plate by helium plasma irradiation. The nanostructure consisting of W metal was partially oxidized to form WO3 on exposure to air, and the resulting surface exhibited a broad photoabsorption in the range from 1 to 5 eV. We examined photoinduced reaction of methylene blue (MB) on the material. It was found that the partially and fully oxidized surface nanostructures were able to promote a decolorization of MB under photoirradiation even with the near-infrared light (< 1:55 eV), whose energy is lower than the band gap of WO3. The reaction rate was varied with the fraction of W and WO3 on the surface layers, that is, the partially oxidized sample promoted the reaction at a higher rate than the fully oxidized one. It is also found that the reaction rate decreased with time, which would be caused by the products accumulation on the surface and the surface oxidation.
关键词： Scanning electron microscopy (SEM),Tungsten oxide,Surface photochemistry,Plasma processing,Nano-wires, quantum wires, and nanotubes,Visible/ultraviolet absorption spectroscopy, X-ray photoelectron spectroscopy
更新于2025-09-23 15:21:01
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Charge Transfer Complex of Thioxanthonephenacyl Sulfonium Salt as Visible Light Photoinitiator for Free Radical and Cationic Polymerizations.
摘要： A new double chromophoric sulfonium salt photoinitiator possessing both thioxanthone and phenacyl groups, namely 2-isopropylthioxanthonium phenacyl hexafluoroantimonate (ITXPhenS) was synthesized and characterized. ITXPhenS can form charge transfer complex (CTC) with the donor N, N-dimethyl aniline (DMA) with absorption characteristics in the visible range as confirmed by spectral analysis, cyclic voltammetry (CV) and density functional theory (DFT). The extension of the absorbance shift can be controlled by the ITXPhenS to DMA ratio. The ability of the CTC to initiate free radical and cationic polymerization reactions of various monomers under visible and natural sunlight is demonstrated. The proposed mechanism assumes the generation of radical and ionic species by the heterolytic and/or homolytic cleavage of ITXPhenS within the CTC followed by electron transfer reactions.
关键词： photochemistry,density functional calculations,cyclic voltammetry,polymerization,charge transfer
更新于2025-09-23 15:21:01