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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
摘要： We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes and determine the corresponding photochemical mechanism. Then, we describe a protocol to perform ring-opening metathesis polymerization (ROMP) in solution and in miniemulsion using this NHC-photogenerating system. To photogenerate IMes, a system comprising 2-isopropylthioxanthone (ITX) as the sensitizer and 1,3-dimesitylimidazolium tetraphenylborate (IMesH+BPh4-) as the protected form of NHC is employed. IMesH+BPh4- can be obtained in a single step by anion exchange between 1,3-dimesitylimidazolium chloride and sodium tetraphenylborate. A real-time steady-state photolysis setup is described, which hints that the photochemical reaction proceeds in two consecutive steps: 1) ITX triplet is photo-reduced by the borate anion and 2) subsequent proton transfer takes place from the imidazolium cation to produce the expected NHC IMes. Two separate characterization protocols are implemented. Firstly, CS2 is added to the reaction media to evidence the photogeneration of NHC through formation of the IMes-CS2 adduct. Secondly, the amount of NHC released in situ is quantified using acid-base titration. The use of this NHC photo-generating system for the ROMP of norbornene is also discussed. In solution, a photopolymerization experiment is conducted by mixing ITX, IMesH+BPh4-, [RuCl2(p-cymene)]2 and norbornene in CH2Cl2, then irradiating the solution in a UV reactor. In a dispersed medium, a monomer miniemulsion is first formed then irradiated inside an annular reactor to produce a stable poly(norbornene) latex.
关键词： photoreactivity,ring-opening,miniemulsion,metathesis,Chemistry,photolysis,Polymer,photochemistry,Issue 141,NHC,photoreactor,carbene,ROMP
更新于2025-09-09 09:28:46
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Photoorganocatalytic Radical Reaction of Cinnamaldehydes and Olefins
摘要： Melchiorre and co-workers report a visible-light-mediated enantioselective radical reaction between cinnamaldehydes and a broad range of olefins that proceeds via a chiral excited-state iminium ion. The reaction was successfully extended to a three-component radical cascade reaction.
关键词： photochemistry,asymmetric radical reaction,cascade reaction,alkenes,cinnamaldehydes
更新于2025-09-09 09:28:46
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T1 Population as the Driver of Excited-State Proton-Transfer in 2-Thiopyridone
摘要： Excited state proton transfer (ESPT) is a fundamental process in bio–molecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2-thiopyridone, employing transient N 1s X-ray absorption spectroscopy and multi-configurational spectrum simulations. Photo-excitations to the singlet S2 and S4 states both relax promptly via intersystem crossing to the triplet T1 state. The T1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation via ESPT in secondary intersystem crossing to the S0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, that is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.
关键词： intersystem crossing,nitrogen,excited-state proton-transfer,photochemistry,X-ray absorption
更新于2025-09-09 09:28:46
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Patterned Surface Activation of Cyclo-Olefin Polymers for Biochip Applications
摘要： Two different surface activation methods (UV/ozone and oxygen plasma treatment) were applied for patterned surface activation of cyclo-olefin polymer (COP) surfaces combined with different masking techniques (metal shadow mask and protective tape). Surface properties were characterized by various methods such as contact angle measurement, ATR-IR, XPS and Surface enhanced ellipsometric contrast (SEEC) microscopy. UV/ozone and oxygen plasma allowed for patterned surface modification of COP leading to the formation of carboxylic and hydroxyl groups on the activated part of the surface. Stability against organic solvents was determined by rinsing the activated substrates with 2-propanol. For UV/ozone treatment it was found that a thin film of degradation products remains on the COP surface and is at least partly removed in the following washing or rinsing steps.
关键词： polymer photochemistry,Biofunctionalization,plasma modification,surface modification
更新于2025-09-09 09:28:46
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Characterisation and improvement of <i>j</i>(O<sup>1</sup>D) filter radiometers
摘要： Atmospheric O3 → O(1D) photolysis frequencies j (O1D) are crucial parameters for atmospheric photochemistry because of their importance for primary OH formation. Filter radiometers have been used for many years for in situ field measurements of j (O1D). Typically the relationship between the output of the instruments and j (O1D) is non-linear because of changes in the shape of the solar spectrum dependent on solar zenith angles and total ozone columns. These non-linearities can be compensated for by a correction method based on laboratory measurements of the spectral sensitivity of the filter radiometer and simulated solar actinic flux density spectra. Although this correction is routinely applied, the results of a previous field comparison study of several filter radiometers revealed that some corrections were inadequate. In this work the spectral characterisations of seven instruments were revised, and the correction procedures were updated and harmonised considering recent recommendations of absorption cross sections and quantum yields of the photolysis process O3 → O(1D). Previous inconsistencies were largely removed using these procedures. In addition, optical interference filters were replaced to improve the spectral properties of the instruments. Successive determinations of spectral sensitivities and field comparisons of the modified instruments with a spectroradiometer reference confirmed the improved performance. Overall, filter radiometers remain a low-maintenance alternative of spectroradiometers for accurate measurements of j (O1D) provided their spectral properties are known and potential drifts in sensitivities are monitored by regular calibrations with standard lamps or reference instruments.
关键词： atmospheric photochemistry,photolysis frequencies,spectral sensitivity,correction factors,filter radiometers
更新于2025-09-04 15:30:14
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Synthesis, crystal structure, photoluminescence and photochemistry of bis(triphenylphosphine)silver(I) flavonolate
摘要： The complex Ag(I)(flavonolate)(PPh3)2 has been prepared and characterized including the crystal structure. This compound shows in degassed solution two emission bands, a fluorescence at λmax?=?505 nm and a phosphorescence at λmax?=?780 nm. Both emissions originate from lowest-energy flavonolate intraligand excited singlet and triplet states, respectively. In the presence of oxygen, the phosphorescence disappears and the complex becomes light-sensitive. The flavonolate ligand undergoes a photooxidation by oxygen.
关键词： crystal structure,silver(I),photochemistry,photoluminescence,flavonolate
更新于2025-09-04 15:30:14
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Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response
摘要： Carbon dots (CDs) are an emerging family of nanosystems displaying a range of fascinating properties. Broadly speaking, they can be described as small, surface-functionalized carbonaceous nanoparticles characterized by an intense and tunable ?uorescence, a marked sensitivity to the environment and a range of interesting photochemical properties. CDs are currently the subject of very intense research, motivated by their possible applications in many ?elds, including bioimaging, solar energy harvesting, nanosensing, light-emitting devices and photocatalyis. This review covers the latest advancements in the ?eld of CDs, with a focus on the fundamental understanding of their key photophysical behaviour, which is still very debated. The photoluminescence mechanism, the origin of their peculiar ?uorescence tunability, and their photo-chemical interactions with coupled systems are discussed in light of the latest developments in the ?eld, such as the most recent results obtained by femtosecond time-resolved experiments, which have led to important steps forward in the fundamental understanding of CDs. The optical response of CDs appears to stem from a very complex interplay between the electronic states related to the core structure and those introduced by surface functionalization. In addition, the structure of CD energy levels and the electronic dynamics triggered by photo-excitation ?nely depend on the microscopic structure of any speci?c sub-type of CD. On the other hand, this remarkable variability makes CDs extremely versatile, a key bene?t in view of their very wide range of applications.
关键词： femtosecond,photophysics,ultrafast,carbon dots,nanocarbon,photochemistry,fluorescence
更新于2025-09-04 15:30:14
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Computational investigation into the fluorescence of luciferin analogues
摘要： Luciferin analogues that display bioluminescence at speci?c wavelengths can broaden the scope of imaging and biological assays, but the need to design and synthesize many new analogues can be time-consuming. Employing a collection of previously synthesized and characterized aminoluciferin analogues, we demonstrate that computational TD-DFT methods can accurately reproduce and explain experimentally measured ?uorescence wavelengths. The best computational approach yields a correlation with experiment of r = 0.98, which we expect to guide and accelerate the further development of luciferin analogues.
关键词： photochemistry,computational,luciferin
更新于2025-09-04 15:30:14
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Impacts of Cys392, Asp393, and ATP on the FAD Binding, Photoreduction, and the Stability of the Radical State of Chlamydomonas reinhardtii Cryptochrome
摘要： Plant cryptochromes (CRYs) are blue-light receptors that regulate the light-dependent growth, development and circadian rhythm. A flavin adenine dinucleotide (FAD) cofactor is bound to the photolyase homology region (PHR) of plant CRYs that can be photoreduced to neutral radical state under blue light. This photoreaction may trigger subsequent signal transduction. Plant CRYs can also bind an ATP adjacent to FAD in a pocket of PHR. Chlamydomonas reinhardtii contains a single plant CRY, named Chlamydomonas photolyase homologue 1 (CPH1). In CPH1, Cys392 and Asp393 is located near the FAD cofactor. Here we showed that replacing Cys392 with Ser had little effect on the properties of CPH1. But the C392N mutant showed a faster photoreduction rate, and a significantly lower oxidation rate of the neutral radical state compared with those of wild type CPH1. Substituting an Asn for Asp393 in CPH1 improved the binding affinity for FAD as well as the stability of the neutral radical; but photoreduction of the mutant was severely inhibited. In the presence of ATP, CPH1 and its mutants exhibited significantly higher binding affinity for FAD and slower oxidation of the neutral radical. These results reveal that the residues at site 392 and the presence of ATP can tune the stability of the neutral radical; the Asp at site 393 is crucial for photoreduction; and the photoreduction rate was not merely determined by the stability of the neutral radical in CPH1.
关键词： flavin radicals,biophysics,photochemistry,cryptochrome,photolyase
更新于2025-09-04 15:30:14