Solvent‐Free Photooxidation of Alkanes by Dioxygen with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone via Photoinduced Electron Transfer

Photooxidation of alkanes by dioxygen occurred under visible light irradiation of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) which acts as a super photooxidant. Solvent‐free hydroxylation of cyclohexane and alkanes is initiated by electron transfer from alkanes to the singlet and triplet excited states of DDQ to afford the corresponding radical cations and DDQ^??, as revealed by femtosecond laser‐induced transient absorption measurements. Alkane radical cations readily deprotonate to produce alkyl radicals, which react with dioxygen to afford alkylperoxyl radicals. Alkylperoxyl radicals abstract hydrogen atoms from alkanes to yield alkyl hydroperoxides, accompanied by regeneration of alkyl radicals to constitute the radical chain reactions, so called autoxidation. The radical chain is terminated in the bimolecular reactions of alkylperoxyl radicals to yield the corresponding alcohols and ketones. DDQ^??, produced by the photoinduced electron transfer from alkanes to the excited state of DDQ, disproportionates with protons to yield DDQH₂.     

Combining UV photodissociation action spectroscopy with electron transfer dissociation for structure analysis of gas‐phase peptide cation‐radicals

We report the first example of using ultraviolet (UV) photodissociation action spectroscopy for the investigation of gas‐phase peptide cation‐radicals produced by electron transfer dissociation. z ‐Type fragment ions ^●Gly‐Gly‐Lys⁺, coordinated to 18‐crown‐6‐ether (CE), are generated, selected by mass and photodissociated in the 200–400 nm region. The UVPD action spectra indicate the presence of valence‐bond isomers differing in the position of the C_α radical defect, (α‐Gly)‐Gly‐Lys⁺(CE), Gly‐(α‐Gly)‐Lys⁺(CE) and Gly‐Gly‐(α‐Lys⁺)(CE). The isomers are readily distinguishable by UV absorption spectra obtained by time‐dependent density functional theory (TD‐DFT) calculations. In contrast, conformational isomers of these radical types are calculated to have similar UV spectra. UV photodissociation action spectroscopy represents a new tool for the investigation of transient intermediates of ion‐electron reactions. Specifically, z ‐type cation radicals are shown to undergo spontaneous hydrogen atom migrations upon electron transfer dissociation. Copyright © 2015 John Wiley & Sons, Ltd.     

Generation of 8‐oxo‐7,8‐dihydroguanine in G‐Quadruplexes Models of Human Telomere Sequences by One‐electron Oxidation

The mechanistic aspects of one‐electron oxidation of G‐quadruplexes in the basket (Na⁺ ions) and hybrid (K⁺ ions) conformations were investigated by transient absorption laser kinetic spectroscopy and HPLC detection of the 8‐oxo‐7,8‐dihydroguanine (8‐oxoG) oxidation product. The photo‐induced one‐electron abstraction from G‐quadruplexes was initiated by sulfate radical anions (SO₄˙^?) derived from the photolysis of persulfate ions by 308 nm excimer laser pulses. In neutral aqueous solutions (pH 7.0), the transient absorbance of neutral guanine radicals, G(‐H)˙, is observed following the complete decay of SO₄˙^? radicals (~10 μs after the actinic laser flash). In both basket and hybrid conformations, the G(‐H)˙ decay is biphasic with one component decaying with a lifetime of ~0.1 ms, and the other with a lifetime of 20–30 ms. The fast decay component (~0.1 ms) in G‐quadruplexes is correlated with the formation of 8‐oxoG lesions. We propose that in G‐quadruplexes, G(‐H)˙ radicals retain radical cation character by sharing the N1‐proton with the O⁶‐atom of G in the [G˙⁺: G] Hoogsteen base pair; this [G(‐H)˙: H⁺G G˙⁺: G] leads to the hydration of G˙⁺ radical cation within the millisecond time domain, and is followed by the formation of the 8‐oxoG lesions.     

Proton‐Coupled Electron Transfer of Unsaturated Fatty Acids and Mechanistic Insight into Lipoxygenase

A proton‐coupled electron transfer (PCET) process plays an important role in the initial step of lipoxygenases to produce lipid radicals which can be oxygenated by reaction with O₂ to yield the hydroperoxides stereoselectively. The EPR spectroscopic detection of free lipid radicals and the oxygenated radicals (peroxyl radicals) together with the analysis of the EPR spectra has revealed the origin of the stereo‐ and regiochemistry of the reaction between O₂ and linoleyl (= (2Z)‐10‐carboxy‐1‐[(1Z)‐hept‐1‐enyl]dec‐2‐enyl) radical in lipoxygenases. The direct determination of the absolute rates of H‐atom‐transfer reactions from a series of unsaturated fatty acids to the cumylperoxyl (= (1‐methyl‐1‐phenylethyl)dioxy) radical by use of time‐resolved EPR at low temperatures together with detailed kinetic investigations on both photoinduced and thermal electron‐transfer oxidation of unsaturated fatty acids provides the solid energetic basis for the postulated PCET process in lipoxygenases. A strong interaction between linoleic acid (= (9Z,12Z)‐octadeca‐9,12‐dienoic acid) and the reactive center of the lipoxygenases (Fe^III? OH) is suggested to be involved to make a PCET process to occur efficiently, when an inner‐sphere electron transfer from linoleic acid to the Fe^III state is strongly coupled with the proton transfer to the OH group.     

Structural and Spectroscopic Evidence for Marginal Metal‐to‐Ligand Charge Transfer in Complexes Pt(abpy)Me3X,abpy = 2,2′‐Azobispyridine,X = Cl,Br, I

The title complexes (X = Cl, 1a ; X = Br, 1b ; X = I, 1c ) could be characterized by ¹H‐NMR spectroscopy and were partially studied by X‐ray diffraction ( 1b,c ), cyclic voltammetry and UV‐Vis spectroscopy ( 1b ). The short N=N bonds of about 1.26Å, the occurrence of only weak charge transfer absorptions in the visible, the rather small shift of the reduction potential, and the small g anisotropy in the EPR spectrum of 1b^{˙ ?} indicate an only a marginal π interaction between the organometallic Pt^IV fragments and the excellent π acceptor abpy.     

Visible‐Light‐Responsive Reversible Photoacid Based on a Metastable Carbanion

A new photoacid that reversibly changes from a weak to a strong acid under visible light was designed and synthesized. Irradiation generated a metastable state with high C?H acidity due to high stability of a trifluoromethyl‐phenyl‐tricyano‐furan (CF₃PhTCF) carbanion. This long‐lived metastable state allows a large proton concentration to be reversibly produced with moderate light intensity. Reversible pH change of about one unit was demonstrated by using a 0.1 mM solution of the photoacid in 95 % ethanol. The quantum yield was calculated to be as high as 0.24. Kinetics of the reverse process can be fitted well to a second‐order‐rate equation with k=9.78×10² M ^?1 s^?1. Response to visible light, high quantum yield, good reversibility, large photoinduced proton concentration under moderate light intensity, and good compatibility with organic media make this photoacid a promising material for macroscopic control of proton‐transfer processes in organic systems.     

Efficient Hyperpolarization of U‐13C‐Glucose Using Narrow‐Line UV‐Generated Labile Free Radicals

Free radicals generated by UV‐light irradiation of a frozen solution containing a fraction of pyruvic acid (PA) have demonstrated their dissolution dynamic nuclear polarization (dDNP) potential, providing up to 30 % [1‐¹³C]PA liquid‐state polarization. Moreover, their labile nature has proven to pave a way to nuclear polarization storage and transport. Herein, differently from the case of PA, the issue of providing dDNP UV‐radical precursors (trimethylpyruvic acid and its methyl‐deuterated form) not involved in any metabolic pathway was investigated. The ¹³C dDNP performance was evaluated for hyperpolarization of [U‐¹³C₆,1,2,3,4,5,6,6‐d₇]‐d ‐glucose. The generated UV‐radicals proved to be versatile and highly efficient polarizing agents, providing, after dissolution and transfer (10 s), a ¹³C liquid‐state polarization of up to 32 %.     

Thioxanthone–anthracene‐9‐carboxylic acid as radical photoinitiator in the presence of atmospheric air

Thioxanthone–anthracene‐9‐carboxylic acid (TX‐ANCA) namely 14‐oxo‐14H‐naphthol [2,3‐b]thioxanten‐12‐carboxylic acid, is synthesized and characterized as part of our continuing interest for syntheses of polyaromatic initiators. Photoinitiator, TX‐ANCA have good absorption properties in the UV and visible region of the electromagnetic spectrum (ɛ₃₇₀: 9080 M⁻¹cm⁻¹, ɛ₄₃₀: 6151 M⁻¹ cm⁻¹). The fluorescence quantum yield is calculated as 0.1 which is slightly higher than of the parent thioxanthone compound (φ_f: 0.07). The phosphorescence lifetime is found to be 39 ms. The possible initiating mechanism of TX‐ANCA is based on photoexcitation of TX‐ANCA and quenching of triplet excited states of TX‐ANCA by molecular oxygen generates singlet oxygen. Singlet oxygen reacts with the anthracene moiety of TX‐ANCA possibly forms an endoperoxide. The endoperoxides undergoes photochemical or thermal decomposition to form radicals which are able to initiate free radical polymerization. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1878–1883     

Ruthenium(II)–Polyimine–Coumarin Light‐Harvesting Molecular Arrays: Design Rationale and Application for Triplet–Triplet‐Annihilation‐Based Upconversion

Ru^II–bis‐pyridine complexes typically absorb below 450 nm in the UV spectrum and their molar extinction coefficients are only moderate (ε<16 000 M ^?1 cm^?1). Thus, Ru^II–polyimine complexes that show intense visible‐light absorptions are of great interest. However, no effective light‐harvesting ruthenium(II)/organic chromophore arrays have been reported. Herein, we report the first visible‐light‐harvesting Ru^II–coumarin arrays, which absorb at 475 nm (ε up to 63 300 M ^?1 cm^?1, 4‐fold higher than typical Ru^II–polyimine complexes). The donor excited state in these arrays is efficiently converted into an acceptor excited state (i.e., efficient energy‐transfer) without losses in the phosphorescence quantum yield of the acceptor. Based on steady‐state and time‐resolved spectroscopy and DFT calculations, we proposed a general rule for the design of Ru^II–polypyridine–chromophore light‐harvesting arrays, which states that the ¹IL energy level of the ligand must be close to the respective energy level of the metal‐to‐ligand charge‐transfer (M LCT) states. Lower energy levels of ¹IL/³IL than the corresponding ¹M LCT/³M LCT states frustrate the cascade energy‐transfer process and, as a result, the harvested light energy cannot be efficiently transferred to the acceptor. We have also demonstrated that the light‐harvesting effect can be used to improve the upconversion quantum yield to 15.2 % (with 9,10‐diphenylanthracene as a triplet‐acceptor/annihilator), compared to the parent complex without the coumarin subunit, which showed an upconversion quantum yield of only 0.95 %.     

Stable All‐Organic Radicals with Ambipolar Charge Transport

A series of neutral long‐lived purely organic radicals based on the stable [4‐(N‐carbazolyl)‐2,6‐dichlorophenyl]bis(2,4,6‐trichlorophenyl)methyl radical adduct (Cbz‐TTM) is reported herein. All compounds exhibit ambipolar charge‐transport properties under ambient conditions owing to their radical character. High electron and hole mobilities up to 10^?2 and 10^?3 cm² V^?1 s^?1, respectively, were achieved. Xerographic single‐layered photoreceptors were fabricated from the radicals studied herein, exhibiting good xerographic photosensitivity across the visible spectrum.     

New diorganotin(IV) complexes of Schiff base derived from 4‐amino‐3‐hydrazino‐5‐mercapto‐4H‐1,2,4‐triazole: Synthesis,structural characterization,density functional theory studies,atoms‐in‐molecules analysis and antifungal activity

New diorganotin(IV) complexes of a Schiff base (HL) having general formula R₂Sn(L)Cl (where L is the monoanion of HL and R = n‐Bu or Ph) have been synthesized and characterized using elemental analysis, infrared, NMR (¹H, ¹³C, ¹¹⁹Sn) and UV–visible spectroscopies and mass spectrometry. These investigations suggest that in these 1:1 monomeric derivatives the Schiff base ligand acts in a monoanionic bidentate manner coordinating through the O_phenolic and N_azomethine, with proposed distorted trigonal bipyramidal geometry around tin with O_phenolic and two organic groups in the equatorial plane and the N_azomethine and the third organic group in axial positions. The proposed structures have been validated by density functional theory (DFT)‐based quantum chemical calculations at the B3LYP/6‐31G(d,p)/Def2‐SVP (Sn) level of theory. The simulated UV–visible spectrum was obtained with the time‐dependent DFT method in the gas phase and in the solvent field with the integral equation formalism–polarizable continuum model. A comparative analysis of the experimental vibrational frequencies and simulated harmonic frequencies indicates a good correlation between them. An insight into the intramolecular bonding and interactions among bonds in organotin(IV) complexes of HL was obtained by means of natural bond orbital analysis. The topological and energetic properties of the electron density distribution for the tin–ligand interaction in R₂Sn(L)Cl have been theoretically calculated at the bonds around the central tin atom in terms of atoms‐in‐molecules theory. The R₂Sn(L)Cl complexes were screened for their in vitro antifungal activity against chosen fungal strains.     

Simultaneous determination of NG‐monomethyl‐l‐arginine,NG,NG‐dimethyl‐l‐arginine,NG,NG′‐dimethyl‐l‐arginine,and l‐arginine using monolithic silica disk‐packed spin columns and a monolithic silica column

We have developed and validated a high‐performance liquid chromatography method that uses monolithic silica disk‐packed spin columns and a monolithic silica column for the simultaneous determination of N^G‐monomethyl‐l ‐arginine, N^G,N^G‐dimethyl‐l ‐arginine, and N^G,N^G′‐dimethyl‐l ‐arginine in human plasma. For solid‐phase extraction, our method employs a centrifugal spin column packed with monolithic silica bonded to propyl benzenesulfonic acid as a cation exchanger. After pretreatment, the methylated arginines are converted to fluorescent derivatives with 4‐fluoro‐7‐nitro‐2,1,3‐benzoxadiazole, and then the derivatives are separated on a monolithic silica column. l ‐Arginine concentration was also determined in diluted samples. Standard calibration curves revealed that the assay was linear in the concentration range 0.2–1.0 μM for methylated arginines and 40–200 μM for l ‐arginine. Linear regression of the calibration curve yielded equations with correlation coefficients of 0.999 (r²). The sensitivity was satisfactory, with a limit of detection ranging from 3.75 to 9.0 fmol for all four compounds. The RSDs were 4.3–4.8% (intraday) and 3.0–6.8% (interday). When this method was applied to samples from six healthy donors, the detected concentrations of N^G‐monomethyl‐l ‐arginine, N^G,N^G‐dimethyl‐l ‐arginine, N^G,N^G′‐dimethyl‐l ‐arginine and l ‐arginine were 0.05 ± 0.01, 0.41 ± 0.07, 0.59 ± 0.11, and 83.8 ± 30.43 μM (n = 6), respectively.     

Scavenging activity of C4‐hydroxyphenyl‐ and polyhydroxyphenyl‐1,4‐dihydropyridines toward free radicals

The radical‐scavenging ability of synthesized C4‐phenolic‐substituted 1,4‐dihydropyridines (1,4‐DHPs) toward 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) and alkyl/alkylperoxyl ABAP‐derived radicals at pH 7.4 was assessed by UV–visible spectroscopy. Reactivity of 1,4‐DHPs toward DPPH^? was measured by following the decay of the absorption corresponding to the radical λ_max at 525 nm, permitting the calculation of EC₅₀, t_EC50, and antiradical efficiency values. Pseudo–first‐order kinetic rate constants for the reactivity between the C4‐phenolic‐substituted 1,4‐DHP compounds and alkyl/alkylperoxyl ABAP‐derived radicals were followed by the decrease in λ_max at 356 nm corresponding to 1,4‐DHP moiety. C4‐phenolic‐substituted 1,4‐DHPs were more reactive toward alkyl free radicals than the other tested radicals. The 3,4,5‐trihydroxyphenyl‐1,4‐DHP was the most reactive derivative toward this radical with a kinetic rate constant value of 513.2 s^?1. Also, this derivative was the most effective toward the DPPH^? radical with the lowest EC₅₀ value (5.08 µM). Comparative studies revealed that synthesized 1,4‐DHPs were more reactive than commercial 1,4‐DHPs. The scavenging mechanism involves the contribution of both pharmacophores, that is, hydroxyphenyl and 1,4‐DHP rings, which was supported by the identification of the reaction products. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 810–820, 2012     

Synthesis of 1,4‐Diethynyl‐ and 1,1,4,4‐Tetraethynylbutatrienes

In this paper, we report the synthesis and opto‐electronic properties of differentially substituted 1,4‐diethynyl‐ and 1,1,4,4‐tetraethynylbuta‐1,2,3‐trienes. These novel chromophores greatly extend the series of building modules for oxidative coupling, which includes 1,2‐diethynyl‐ and 1,1,2,2‐tetraethynylethenes and 1,3‐diethynylallenes (Fig. 1). A general synthesis of 1,1,4,4‐tetraethynylbutatrienes, which tolerates a significant number of peripheral substituents, starts from pentadiynols that are oxidized to the corresponding dialkynyl ketones, followed by Corey–Fuchs dibromo‐olefination, and transition metal mediated dimerization (Schemes 2 and 3). A similar protocol, including oxidation of propargyl aldehydes, dibromo‐olefination, and dimerization yields the less stable 1,4‐diethynylbutatrienes (Scheme 4). Attempts to prepare 1,1,4,4‐tetraethynylbutatrienes with four terminal electron‐donor‐substituted aryl groups failed so far, mainly due to difficulties in the dibromoolefination step (Scheme 6). cis‐trans‐Isomerization of differentially substituted 1,1,4,4‐tetraethynylbutatrienes is remarkably facile, with barriers to rotation in the range of those for peptide bond isomerization (ΔG^≠≈20 kcal mol^?1). Barriers to rotation of 1,4‐diethynylbutatrienes are higher (ΔG^≠≈25 kcal mol^?1), allowing in some cases the isolation of pure isomers. Both UV/VIS spectroscopy (Figs. 2 and 3) and electrochemical studies (Table) demonstrate that the all‐C‐cores in diethynyl‐ and tetraethynylbutatrienes have strong electron‐acceptor properties that are greatly enhanced with respect to those of diethynyl‐ and tetraethynylethenes with two C(sp)‐atoms less. Substitution with peripheral electron donor groups leads to efficient intramolecular charge‐transfer interactions, as evidenced by intense, bathochromically shifted longest‐wavelength bands in the UV/VIS spectra.     

Structure‐Dependent Photoinduced Electron Transfer in Fullerodendrimers with Light‐Harvesting Oligophenylenevinylene Terminals

Oligophenylenevinylene (OPV)‐terminated phenylenevinylene dendrons G1 – G4 with one, two, four, and eight “side‐arms”, respectively, were prepared and attached to C₆₀ by a 1,3‐dipolar cycloaddition of azomethine ylides generated in situ from dendritic aldehydes and N‐methylglycine. The relative electronic absorption of the OPV moiety increases progressively along the fullerodendrimer family C₆₀G1 – C₆₀G4 , reaching a 99:1 ratio for C₆₀G4 (antenna effect). UV/Vis and near‐IR luminescence and transient absorption spectroscopy was used to elucidate photoinduced energy and electron transfer in C₆₀G1 – C₆₀G4 as a function of OPV moiety size and solvent polarity (toluene, dichloromethane, benzonitrile), taking into account the fact that the free‐energy change for electron transfer is the same along the series owing to the invariability of the donor–acceptor couple. Regardless of solvent, all the fullerodendrimers exhibit ultrafast OPV→C₆₀ singlet energy transfer. In CH₂Cl₂, the OPV→C₆₀ electron transfer from the lowest fullerene singlet level (¹C₆₀*) is slightly exergonic (ΔG_CS≈0.07 eV), but is observed, to an increasing extent, only in the largest systems C₆₀G2 – C₆₀G4 with lower activation barriers for electron transfer. This effect has been related to a decrease of the reorganization energy upon enlargement of the molecular architecture. Structural factors are also at the origin of an unprecedented OPV→C₆₀ electron transfer observed for C₆₀G3 and C₆₀G4 in apolar toluene, whereas in benzonitrile, electron transfer occurs in all cases. Monitoring of the lowest fullerene triplet state by sensitized singlet oxygen luminescence and transient absorption spectroscopy shows that this level is populated through intersystem crossing and is not involved in photoinduced electron transfer.     

The Role of One‐Electron Reduction of Lipid Hydroperoxides in Causing DNA Damage

The in vivo metabolism of plasma lipids generates lipid hydroperoxides that, upon one‐electron reduction, give rise to a wide spectrum of genotoxic unsaturated aldehydes and epoxides. These metabolites react with cellular DNA to form a variety of pre‐mutagenic DNA lesions. The mechanisms of action of the radical precursors of these genotoxic electrophiles are poorly understood. In this work we investigated the nature of DNA products formed by a one‐electron reduction of (13S)‐hydroperoxy‐(9Z,11E)‐octadecadienoic acid (13S‐HPODE), a typical lipid molecule, and the reactions of the free radicals thus generated with neutral guanine radicals, G(?H)^.. A novel approach was devised to generate these intermediates in solution. The two‐photon‐induced ionization of 2‐aminopurine (2AP) within the 2′‐deoxyoligonucleotide 5′‐d(CC[2AP]TCGCTACC) by intense nanosecond 308 nm excimer laser pulses was employed to simultaneously generate hydrated electrons and radical cations 2AP^.+. The latter radicals either in cationic or neutral forms, rapidly oxidize the nearby G base to form G(?H)^.. In deoxygenated buffer solutions (pH 7.5), the hydrated electrons rapidly reduce 13S‐HPODE and the highly unstable alkoxyl radicals formed undergo a prompt β‐scission to pentyl radicals that readily combine with G(?H)^.. Two novel guanine products in these oligonucleotides, 8‐pentyl‐ and N²‐pentylguanine, were identified. It is shown that the DNA secondary structure significantly affects the ratio of 8‐pentyl‐ and N²‐pentylguanine lesions that changes from 0.9:1 in single‐stranded, to 1:0.2 in double‐stranded oligonucleotides. The alkylation of guanine by alkyl radicals derived from lipid hydroperoxides might contribute to the genotoxic modification of cellular DNA under hypoxic conditions. Thus, further research is warranted on the detection of pentylguanine lesions and other alkylguanines in vivo.     

The Effects of Microenvironment Polarity and Dendritic Branching of Aliphatic Hydrocarbon Dendrons on the Self‐Assembly of 2‐Ureido‐4‐pyrimidinones

Two series of aliphatic hydrocarbon‐based G1–G3 dendritic 2‐ureido‐4‐pyrimidinones (UPy) ( S‐Gn )₂ and ( L‐Gn )₂, differing from one another by the distance between the branching juncture to the urea end, were prepared and characterized. These hydrocarbon dendrons were also appended to a p‐aminonitrobenzene solvatochromic chromophore in order to probe their microenvironment polarity. While positive solvatochromism was observed which indicated the chromophore was solvent accessible, there was no significant difference between the microenvironment polarities on going from the G1 to the G3 dendrons. The self‐assembling behavior and tautomeric preference of the dendritic UPy derviatives were examined by ¹H NMR spectroscopy. The dimerization constants (K_dim*) of the DDAA tautomers were unchanged at 10⁷ M ^?1 in CDCl₃ at both 25 and 50 °C, which were comparable to those of UPy compounds bearing other nonpolar substitutents. Furthermore, the lower limits on the K′_dim* of the DADA tautomeric forms of the ( S‐Gn )₂ and ( L‐Gn )₂ series were determined to be 10⁶ and 10⁵ M ^?1 in CDCl₃, respectively. It was found that a closer proximity of the dendron branching juncture to the UPy unit could lead to a destabilization effect on the dimeric states. Hence, the ( L‐Gn )₂ dimers are more stable than those of ( S‐Gn )₂ in the DDAA form, but the latter are more stable than the former in the tautomeric DADA state. This study showed that both the highly nonpolar microenvironment and the proximity of the dendritic branching juncture to the UPy motif could alter the strength and profile of the hydrogen bond‐mediated self‐assembling process.     

Synthesis and Optical Properties of 2,13‐Dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6

A new crown ether of 2,13‐dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6 was synthesized from 2,13‐diformyl‐ dibenzo[b,k]‐18‐crown‐6 with 2‐aminothiophenol. The binding behavior and the optical properties of the crown ether were examined through UV‐visible spectroscopy and fluorescence spectroscopy. When complexed with Na⁺, K⁺, Rb⁺ and Cs⁺ ions, it led to intramolecular charge transfer and caused the changes of the fluorescence spectra. The protonation of the crown ether was also studied.     

Vacancy‐Rich Monolayer BiO2−x as a Highly Efficient UV,Visible, and Near‐Infrared Responsive Photocatalyst

Vacancy‐rich layered materials with good electron‐transfer property are of great interest. Herein, a full‐spectrum responsive vacancy‐rich monolayer BiO_2?x has been synthesized. The increased density of states at the conduction band (CB) minimum in the monolayer BiO_2?x is responsible for the enhanced photon response and photo‐absorption, which were confirmed by UV/Vis‐NIR diffuse reflectance spectra (DRS) and photocurrent measurements. Compared to bulk BiO_2?x, monolayer BiO_2?x has exhibited enhanced photocatalytic performance for rhodamine B and phenol removal under UV, visible, and near‐infrared light (NIR) irradiation, which can be attributed to the vacancy V_Bi‐O′′′ as confirmed by the positron annihilation spectra. The presence of V_Bi‐O′′′ defects in monolayer BiO_2?x promoted the separation of electrons and holes. This finding provides an atomic level understanding for developing highly efficient UV, visible, and NIR light responsive photocatalysts.     

Combined experimental and computational modeling studies on 3,5‐dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester

The title compound, 3,5‐Dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester, has been synthesized and structurally characterized by X‐ray single crystal diffraction, elemental analysis, IR spectra, and UV‐Vis spectrum. The crystal belongs to orthorhombic, space group P212121, with a = 5.3829(15), b = 11.193(3), c = 21.824(6) Å, V = 1315.0(6) ų, and Z = 4. The molecules are connected via intermolecular C–H···N hydrogen bonds into 1D infinite chains. The crystal structure is consolidated by the intramolecular C–H···S hydrogen bonds. Furthermore, Density functional theory (DFT) calculations of the structure, stabilities, orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the title compound were performed by means of Gaussian 03W package and taking B3LYP/6‐31G(d) basis set. The time‐dependent DFT (TD‐DFT) calculations have been employed to calculate the electronic spectrum of the title compound, and the UV‐Vis spectra has been discussed on this basis. The results show that DFT method at B3LYP/6‐31G(d) level can well reproduce the structure of the title compound. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012