The development of highly active and selective metal catalysts for efficient oxidation of hydrocarbons and identification of the reactive intermediates in the oxidation catalysis are long-standing ...challenges. In the rapid hydrocarbon oxidation catalyzed by ruthenium(IV) and -(III) porphyrins, the putative Ru(V)-oxo intermediates remain elusive. Herein we report that arylruthenium(III) porphyrins are highly active catalysts for hydrocarbon oxidation. Using catalyst RuIII(TDCPP)(Ph)(OEt2) (H2TDCPP = 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin), the oxidation of C–H bonds of various hydrocarbons with oxidant m-CPBA at room temperature gave alcohols/ketones in up to 99% yield within 1 h; use of n Bu4NIO4 as a mild alternative oxidant avoided formation of lactone from cyclic ketone in C–H oxidation, and the catalytic epoxidation with up to 99% yield and high selectivity (no aldehydes as side product) was accomplished within 5 min. UV–vis, electrospray ionization–mass spectrometry, resonance Raman, electron paramagnetic resonance, and kinetic measurements and density functional theory calculations lend evidence for the formation of Ru(V)-oxo intermediate RuV(TDCPP)(O)(Ph).
The 3-hydroxyflavone (3-HF) is one of the common fluorescence probes. It has two distinct fluorescence bands: normal form and tautomer form. However, 3-hydroxyflavone has poor performance in water ...because of hydrogen bonding perturbation. The utilization of supramolecular chemistry would improve the fluorescence performance of 3-hydroxyflavone in water. In this paper, it reviews supramolecular chemistry of 3-hydroxyflavone with cyclodextrin and octa acid. Past research has found that the addition of β-cyclodextrin to 3-hydroxyflavone in water would slightly improve the fluorescence intensity of the tautomer form. When adding γ-cyclodextrin to 3-hydroxyflavone in water, the green fluorescence intensity would be enhanced. Finally, the addition of octa acid creates a dry environment for the 3-hydroxyflavone, and it would only have a tautomer form. The ONIOM calculation shows the ways of self-assembly of β- and γ-cyclodextrin. It can explain the difference in ratio between the tautomer form and normal form after understanding the interaction.
Polycyclic Aromatic Hydrocarbons
A pentagon‐heptagon‐embedded polycyclic aromatic hydrocarbon (PAH) consisting of B‐N heteroatoms (BN‐2) is synthesized in only two steps. Combining spectroscopic ...measurements and theoretical calculations, the excited‐state dynamics of the resultant BN‐doped PAHs are well‐investigated, demonstrating both prompt fluorescence and long‐lived delayed fluorescence components with their triplet excited‐state lifetimes in the microsecond time region. More details can be found in article number 2301769 by Shu Seki, Junzhi Liu, and co‐workers.
Tetrazolium salts (TZs) are pervasively utilized as precursors in the dye industry, colorimetric probes in enzyme assays and for exploring nanomaterial toxicity, but its own toxicity is not ...investigated enough so far. Using femtosecond transient absorption spectroscopy, nanosecond pulse radiolysis (ns-PRL), western blotting and UV-vis absorption spectroscopy, here we characterized a neutral tetrazolinyl radical (with the same maximum absorption at 420 nm and different lifetimes of 5.0 and 9.0 μs for two selected TZs), the key intermediate of TZs reduction, and noticed TZs-formazan production under UV light irradiation accompanied by 41% increase in the cross-linking of lysozyme (Lyso, model protein) compared to TZs-free sample, which uncovered the photoenhanced oxidation of TZs towards Lyso. The ns-PRL in a reductive atmosphere simulated the electron/proton donors of amino acid residues in Lyso upon photoexcitation and revealed the reduction mechanism of TZs, as that first followed one-electron-transfer and then probably proton-coupled electron transfer. This is the first time to report on the photoenhanced oxidation mechanism of TZs, which would provide new insights into the applications of TZs in cell biology, "click" chemistry and nanotoxicology.
A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes Ir
(ttp)(IMe)
...
(
), Ir
(oep)(BIMe)
(
), Ir
(oep)(I
Pr)
(
) and Ir
(F
tpp)(IMe)
(
) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 Å and long Ir-C
bonds of 2.100-2.152 Å. Variable-temperature
H NMR analysis of
reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol
. The UV-vis absorption spectra of Ir
(por)-NHC complexes display split Soret bands. TD-DFT calculations and resonance Raman experiments show that the higher-energy Soret band is derived from the
MLCT dπ(Ir) → π*(por) transition. The near-infrared phosphorescence of Ir
(por)-NHC complexes from the porphyrin-based
(π, π*) state features broad emission bands at 701-754 nm with low emission quantum yields and short lifetimes (
< 0.01;
< 4 μs). Ir
(por)(IMe)
complexes (por = ttp and oep) are efficient photosensitizers for
O
generation (
= 0.64 and 0.88) and are catalytically active in the light-induced aerobic oxidation of secondary amines and arylboronic acid. The bis-NHC complexes exhibit potent dark cytotoxicity towards a panel of cancer cells with IC
values at submicromolar levels. The cytotoxicity of these complexes could be further enhanced upon light irradiation with IC
values as low as nanomolar levels in association with the light-induced generation of reactive oxygen species (ROS). Bioimaging of Ir
(oep)(IMe)
(
) treated cells indicates that this Ir complex mainly targets the endoplasmic reticulum. Ir
(oep)(IMe)
catalyzes the photoinduced generation of singlet oxygen and triggers protein oxidation, cell cycle arrest, apoptosis and the inhibition of angiogenesis. It also causes pronounced photoinduced inhibition of tumor growth in a mouse model of human cancer.
Excited state intramolecular proton transfer (ESIPT) in 3-hydroxyflavone (3HF) has been known for its dependence on excitation wavelength. Such a behavior violates Kasha's rule, which states that the ...emission and photochemistry of a compound would only take place from its lowest excited state. The photochemistry of 3HF was studied using femtosecond transient absorption spectroscopy at a shorter wavelength excitation (266 nm), and these new experimental findings were interpreted with the aid of computational studies. These new results were compared with those from previous studies that were obtained with a longer wavelength excitation and show that there exists a pathway of proton transfer that bypasses the normal first excited state from the higher excited state to the tautomer from first excited state. The experimental data correlate with the electron density difference calculations such that the proton transfer process is faster on the longer excitation wavelength than compared to the shorter excitation wavelength.
This research article uses density functional theory (DFT) to study photoinduced borylation. This work examined the electron donor‐acceptor complex (EDA) of bis(catecholato)diboron with different ...redox‐active leaving groups and bis(pinacol)diboron with aryl N‐hydroxyphthalimide. The results of these DFT studies show the complex ratio of B2cat2 and N, N‐dimethylacetamide (DMA) should be 1 : 2 which is consistent with the experimental results in the literature. We further proposed a reaction mechanism and calculated the energies associated with each step.
The bis(catecholato)diboron(B2cat2) in dimethylacetamide (DMA) is popular boron source in photoinduced borylation. This article has studied the complex by DFT. It first compares the stoichiometry between the B2cat2 with 1 DMA and B2cat2 with 2 DMA. Based on the coordination of boron compound, two type of photoinduced borylation reaction mechanism were discussed and compared.
Metal‐TADF (thermally activated delayed fluorescence) emitters hold promise in the development of next generation light‐emitting materials for display and lighting applications, examples of which ...are, however, largely confined to CuI and recently AuI, AgI, and AuIII emitters. Herein is described the design strategy for an unprecedented type of metal‐TADF emitter based on inexpensive tungsten metal chelated with Schiff base ligand that exhibit high emission quantum yields of up to 56 % in solutions and 84 % in thin‐film (5 wt % in 1,3‐bis(N‐carbazolyl)benzene, mCP) at room temperature. Femtosecond time‐resolved emission (fs‐TRE) spectroscopy and DFT calculations were undertaken to decipher the TADF properties. Solution‐processed OLEDs fabricated with the W‐TADF emitter demonstrated external quantum efficiency (EQE) and luminance of up to 15.6 % and 16890 cd m−2, respectively.
A lightbulb moment for WVI complexes: Incorporation of arylamino substituents into the ligand scaffold leads to the realization of the first WVI Schiff base complex with TADF properties, which shows Φem of 56 % in solution and 84 % in thin film at room temperature. High‐efficiency solution‐processed W‐OLEDs were fabricated, exhibiting a maximum EQE and luminance of up to 15.6 % and 16890 cd m−2, respectively.
Abstract
Nitrenium ions are important reactive intermediates in both chemistry and biology. Although singlet nitrenium ions are well-characterized by direct methods, the triplet states of nitrenium ...ions have never been directly detected. Here, we find that the excited state of the photoprecursor partitions between heterolysis to generate the singlet nitrenium ion and intersystem crossing (ISC) followed by a spontaneous heterolysis process to generate the triplet
p
-iodophenylnitrenium ion (
np
). The triplet nitrenium ion undergoes ISC to generate the ground singlet state, which ultimately undergoes proton and electron transfer to generate a long-lived radical cation that further generates the reduced p-iodoaniline. Ab Initio calculations were performed to map out the potential energy surfaces to better understand the excited state reactivity channels show that an energetically-accessible singlet-triplet crossing lies along the
N-N
stretch coordinate and that the excited triplet state is unbound and spontaneously eliminates ammonia to generate the triplet nitrenium ion. These results give a clearer picture of the photophysical properties and reactivity of two different spin states of a phenylnitrenium ion and provide the first direct glimpse of a triplet nitrenium ion.
Ultraviolet irradiation of DNA produces electronic excited states that predominantly eliminate the excitation energy by returning to the ground state (photostability) or following minor pathways into ...mutagenic photoproducts (photodamage). The cyclobutane pyrimidine dimer (CPD) formed from photodimerization of thymines in DNA is the most common form of photodamage. The underlying molecular processes governing photostability and photodamage of thymine-constituted DNA remain unclear. Here, a combined femtosecond broadband time-resolved fluorescence and transient absorption spectroscopies were employed to study a monomer thymidine and a single-stranded thymine oligonucleotide. We show that the protecting deactivation of a thymine multimer is due to an ultrafast single-base localized stepwise mechanism where the initial excited state decays via a doorway state to the ground state or proceeds via the doorway state to a triplet state identified as a major precursor for CPD photodamage. These results provide new mechanistic characterization of and a dynamic link between the photoexcitation of DNA and DNA photostability and photodamage.
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