Pulse and Continuous Radiolyses of the Europium and Neodymium Decatungstate Anions in Aqueous Solution

We have studied the behavior of aqueous solutions of the [M⁽³⁺⁾(W₅-O₁₈^(6-))₂]⁹⁻ complexes (M = Eu or Nd) under pulse and continuous radiolysis conditions. Both complexes react with e⁻_aq at a diffusion controlled rate. For the Nd³⁺ complex in solution containing 1% 2-propanol, the decay of the e⁻_aq absorption was accompanied by the formation of a broad absorption band in the visible (λ_max 600–650 nm), with a further increase in absorption up to 2 ms. For the Eu³⁺ complex under the same conditions, the decay of the e⁻_aq absorption was accompanied by the formation of an absorption maximum at ∼370 nm, which is characteristic of Eu²⁺ species. On a longer time scale, a relatively intense absorption arose in the visible (λ_max 600–650 nm) according to a complicated kinetic behavior. The two complexes exhibited a quite similar behavior in continuous radiolysis experiments. Blue products (λ_max 600–650 nm) were formed and, for the Eu³⁺ complex, the disappearance of the Eu³⁺ emission was observed. Even after high irradiation doses, the absorption (and, for Eu³⁺, emission) spectra of the solutions were quantitatively regenerated by air oxidation. The behavior of the Nd³⁺ complex is interpreted on the basis of the reduction of a W₅ O₁₈⁶⁻ ligand by e⁻_aq and alcohol radicals, followed by protonation. For the Eu³⁺ complex, the reduction by e⁻_aq causes mainly the formation of a Eu²⁺ complex. On a longer time scale, protonation and/or reaction with alcohol radicals drive back the electron from Eu²⁺ to the W₅O₁₈⁶⁻ ligands, with formation of stable blue products.     

Photooxidation von Leukofarbstoffen. VIII. Kurzzeitspektroskopische Untersuchungen zum Mechanismus der Photooxidation von Leukokristallviolett

Photooxidation of Leuco Dyes. VIII. Time Resolved Investigations of the Mechanism of the Photooxidation of Leucocrystal Violet The photooxidation of leucocrystal violet has been reexamined by means of conventional and laser flash photolysis as well as spin trap experiments. Three radical transients have been observed and assigned to the cation radical (λ_max ≈ 490, 530 nm), the neutral radical with one NCH₃ CH₂ moiety (λ_max ≈ 480 nm) and the triphenyl methyl radical derivative (λmax ≈ 400 nm).     

Characterization of blends of naphthalene-containing polymers with poly(alkyl methacrylates) by combined steady-state fluorescence spectroscopy and fluorescence decay measurements

The extent of mixing in two-component solution-cast films of poly(2-vinyl naphthalene) (P2VN) and poly(2-iso-propenyl naphthalene) (P2IPN) with poly(methyl methacrylate) and poly(n-butyl methacrylate) was studied by steady-state and time-resolved fluorescence spectroscopy. The steady-state fluorescence spectrum of 1% P2IPN in the two poly(alkyl methacrylates) evolves from 100% monomer emission (λ_max = 340 nm) to >70% excimer emission (λ_max = 390 nm) as its molecular weight increases from 1900 to 278000. Despite such clear-cut changes in the steady-state spectra on phase separation, the fluorescence decays were nonexponential for all mixed films. Triple-exponential decay functions were necessary to describe excimer decays at 430 nm and monomer decays at 340 nm. Moreover, the fluorescence decays varied slightly across the excimer emission band, and changed significantly when the polymer films were annealed. Studies on blends containing from 1 to 100% of P2VN and P2IPN established that this multicomppnent fluorescence decay behavior is intrinsicto the naphthalene-containing polymer phase, it is proposed that excimers formed between chromophores in meso and racemic dyads have different mean decay times and that imperfectly aligned chromophore pairs lead to an additional short-lived excimer decay component.     

Reversible Photoisomerisierungen an Sulfophthalein-Indikatorfarbstoffen. IV. Stopped-Flow-Untersuchungen zum Mechanismus der baseninduzierten Sultonringöffnung

Reversible Photoisomerizations of Sulfophthalein Indicator Dyes. IV. Stopped Flow Investigations on the Mechanism of the Base Induced Sulton Ring Opening The colour formation of rapidly mixed solutions of bromo thymol blue and organic bases in toluene obeys a biexponential rate law. The most probable reaction sequence is: Sulton (colourless) + base ⇌ ring opened H-bridged complex (λ_max ≈ 420 nm) ⇌ H-bridged ion pair (λ_max ≈ 400 nm). Alternative reaction schemes of the same complexity could be ruled out though the underlying kinetic problem is underdetermined. As a generalizing conclusion it is stated that valuable mechanistic and kinetic information may be derived from underdetermined kinetic problems by calculating the ranges of physically meaningful solutions for the unknowns which are compatible with the particular kinetic schemes instead of the unavailable singular solutions.     

Photoluminescence of 8-quinolinolato(trioxo)rhenium(VII)

The complex Re^VIIO₃(oxinate) (oxine=8-quinolinol or 8-hydroxyquinoline) shows a green fluorescence at λ_max=511 nm with φ=0.012 and a very weak red phosphorescence at λ_max=645 nm. Both emissions originate from the lowest-energy ππ* intraligand state of the oxinate ligand. Owing to the d⁰ electron configuration and the high oxidation state of rhenium the heavy atom effect transmitted to the π-electron system of the oxinate ligand is very weak.     

Absorption spectra and CT transitions of compounds containing ReI(CO)3Cl,S2+ and Se2+ as donors and o-benzoquinone diimine as acceptor

The electronic spectra of the cations [(BQDI)Se^II]²⁺ and [(BQDI)S^II]²⁺ are compared to that of [(BQDI)Re^I(CO)₃Cl] with BQDI = o-benzoquinone diimine. While these species show a BQDI-localized ππ¹ absorption between 300 and 360 nm, a longer-wavelength band extends to the visible region. This absorption is attributed to a CT transition from Re^I (λ_max = 538), Se^II (λ_max = 432) and S^II (λ_max = 360 nm) to the π¹ orbitals of BQDI. The analogy of MLCT and related CT transitions involving non-metals as CT donors is emphasized.     

Iodine reaction of vinyl acetate – vinyl propionate copolymers I. Molar absorption coefficients of the copolymer-iodine complexes

Poly(vinyl propionate) was found to form a weak iodine-complex in an aqueous solution of potassium iodide. The complex was colorless under usual conditions differing from the poly(vinyl acetate)iodine complex which had a red-violet colour. Random and block copolymers of vinyl acetate (VAc) and vinyl propionate (VPr) also formed colored iodine complexes. The maximum absorption wave-length (λ_max) of the complex shifted to shorter wave-lengths with decrease in the VAc-fraction of copolymers and to longer wave-lengths with increase in the concentration of added iodine. This shift of λ_max was discussed in connection with the chain length of the polyiodine in the complex. The molar absorption coefficient (?_max) of the complex (defined as absorbance per bound iodine molecule) depended remarkably upon the polymer composition. The dependence of ?_max upon the copolymer composition could be explained by the assumption that the complex consists of two different parts, a strongly colored and a weakly colored one.     

Photocatalytic degradation of 2,2‐bis(4‐hydroxy‐3‐methylphenyl) propane (BPP) based on molecular recognition interaction

BACKGROUND: Endocrine disruptors in the aquatic environment and their potential adverse effects are currently issues of concern. One of these endocrine disruptors is 2,2‐bis(4‐hydroxy‐3‐methylphenyl)propane (BPP). In this work the molecular recognition interaction of BPP with β‐cyclodextrin (β‐CD) was studied using IR spectroscopy and steady state fluorescence spectroscopy, and the photocatalytic degradation behaviour of BPP based on molecular recognition interaction was investigated in a TiO₂/UV–visible (λ_max = 365 nm) system. This might provide a new method for the treatment of some organic pollutants in wastewater. RESULTS: β‐CD reacts with BPP to form a 1:1 inclusion complex, the formation constant of which is 4.94 × 10³ L mol^?1. The photodegradation rate constant of BPP after molecular recognition by β‐CD showed a 1.42‐fold increase in the TiO₂/UV–visible (λ_max = 365 nm) system. The photodegradation of BPP depended on the concentration of β‐CD, the pH value, the gaseous medium and the initial concentration of BPP. The photodegradation efficiency of BPP with molecular recognition was higher than that without molecular recognition. After 100 min of irradiation the mineralisation efficiency of BPP after molecular recognition by β‐CD reached 94.8%, whereas the mineralisation efficiency of BPP before molecular recognition by β‐CD was only 40.6%. CONCLUSION: The photocatalytic degradation of BPP after molecular recognition by β‐CD can be enhanced in the TiO₂/UV‐visible (λ_max = 365 nm) system. This enhancement is dependent on the enhancement of the adsorption of BPP, the moderate inclusion depth of BPP in the β‐CD cavity and the increase in the frontier electron density of BPP after molecular recognition. Copyright © 2008 Society of Chemical Industry     

Characterisation of a coordinated imidazole as a structural model for superoxide dismutase

The copper complex [Cu(HL)](ClO₄)₂·2H₂O, where HL is N-[2-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethyl]–N-(benzimidazol-2-yl)methanimine, has been prepared and characterised by X-ray crystallography and solution absorption spectroscopy. Deprotonation of the benzimidazole moiety in this complex has been investigated by electronic spectroscopy. The results show a definite shift in λ_max for [Cu(HL)]²⁺, at 632–818 nm for the deprotonated [CuL]⁺, in acetonitrile. This complex has been synthesised as a structural homologue to half of the enzyme Cu–Zn superoxide dismutase (SOD) which contains a bridged imidazolate moiety between the two Cu and Zn metal ions.     

Optical properties of bis-(2,4,6-trimethylpyridine)iodine(I) cation: absorption and emission

With regard to its electronic structure, the cation Icoll₂⁺ (coll = collidine or 2,4,6-trimethylpyridine) is viewed as a coordination compound of iodine(I) with a p⁴ electron configuration. The lowest-energy excited state of Icoll₂⁺ is suggested to be a ππ^* collidine intraligand (IL) triplet which appears in absorption (λ_max=332 nm, ε=250) and emission (λ_max=405 nm, φ=0.001, τ∼90 ns). Owing to the heavy-atom effect of iodine this phosphorescence occurs at r.t. The longest-wavelength pp absorption is apparently obscured by the intense spin-allowed IL band at λ_max=268 nm.     

Photochemische Primärprozesse von Xanthenfarbstoffen. I. Blitzlichtspektroskopische Untersuchung der Primärprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. I. Investigations of the Primary Processes of Selenopyronine by Flash Excitation The triplet-state of selenopyronine absorbs light in the whole investigated spectral range (λ_max = 400 nm, 480 nm, 690 nm). As results of the bimolecular triplet decay a half-reduced (λ_max = 430 nm) and a half-oxidized (λ_max = 475 nm) form of the dye are observed. p-Benzoquinone quenches the triplet-state (k₇ = 1,5 · 10⁹ l/mol s) and the results are the half-oxidized form and the p-benzosemiquinone ion. For these two products different decay processes exist. The reducing agents DABCO, EDTA and Hydroquinone also quench the triplet state (k₁₀ = 1,2 · 10⁶ l/mol s, k₁₁ = 1,0 · 10⁶ l/mol s, k₁₂ = 1,0 · 10⁹ l/mol s) and as result the half-reduced form is observed. Measurements with thiopyronine give analogous results, which are in good agreement with investigations published in the literature.     

Photoinduced electron ejection from trihydroxoplumbate(II) in alkaline aqueous solution

In alkaline solution (1 M NaOH) irradiation (λ_ir=266 nm) of Pb(OH)₃⁻ leads to the formation of hydrated electron and oxidized complex in the primary photochemical step. The nascent hydrated electrons react with the ground-state trihydroxoplumbate(II) complexes to form the corresponding reduced Pb(I) compound. The main reaction of this latter species is recombination (synproportionation) with the oxidized (Pb(III)) complex, significantly diminishing the efficiency of the overall light-induced oxidation of Pb(OH)₃⁻ in air-saturated solution.     

Photophysics of Structurally Modified Flavin Derivatives in the Blue‐Light Photoreceptor YtvA: A Combined Experimental and Theoretical Study

The light‐induced processes of two flavin mononucleotide derivatives (1‐ and 5‐deaza flavin mononucleotide, 1DFMN and 5DFMN), incorporated into the LOV domain of YtvA protein from Bacillus subtilis, were studied by a combination of experimental and computational methods. Quantum mechanics/molecular mechanics (QM/MM) calculations were carried out in which the QM part was treated by density functional theory (DFT) using the B3LYP functional for geometry optimizations and the DFT/MRCI method for spectroscopic properties, whereas the MM part was described by the CHARMM force field. 1DFMN is incorporated into the protein binding site, yielding a red‐shifted absorption band (λ_max=530 nm compared to YtvA wild‐type λ_max=445 nm), but does not undergo any LOV‐typical photoreactions such as triplet and photoadduct formation. QM/MM computations confirmed the absence of a channel for triplet formation and located a radiation‐free channel (through an S₁/S₀ conical intersection) along a hydrogen transfer path that might allow for fast deactivation. By contrast, 5DFMN‐YtvA‐LOV shows a blue‐shifted absorption (λ_max=410 nm) and undergoes similar photochemical processes to FMN in the wild‐type protein, both with regard to the photophysics and the formation of a photoadduct with a flavin‐cysteinyl covalent bond. The QM/MM calculations predict a mechanism that involves hydrogen transfer in the T₁ state, followed by intersystem crossing and adduct formation in the S₀ state for the forward reaction. Experimentally, in contrast to wild‐type YtvA, dark‐state recovery in 5DFMN‐YtvA‐LOV is not thermally driven but can only be accomplished after absorption of a second photon by the photoadduct, again via the triplet state. The QM/MM calculations suggest a photochemical mechanism for dark‐state recovery that is accessible only for the adduct with a C4a? S bond but not for alternative adducts with a C5? S bond.     

Computational study of the one- and two-photon absorption properties of macrocyclic thiophene derivatives

The geometrical structure, electronic structure, one-photon and two-photon absorption properties of a series of macrocyclic thiophene derivatives C[3T_DA]_n (n = 2-5) have been studied using density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods theoretically. The results showed that the range of λ⁽¹⁾_maxs is 390-470 nm and λ⁽²⁾_maxs is 640-670 nm, while, both λ⁽¹⁾_max and λ⁽²⁾_max gradually enlarge as increasing the number of the C[3T_DA] unit. And C[3T_DA]_n compounds exhibited large TPA cross-section (δ_max), and the factors influencing on the δ_max values were analyzed in detail. Transition dipole moments M_0k and M_kn play important roles on δ_max. Both π-electron number (N_e) and the product of oscillator strengths from ground state to mediate state (?_0k) and from mediate state to final state (?_kn) are in proportion to δ_max. Moreover, δ_max linearly depends on the static second-order nonlinear optical susceptibilities (β₀).     

Absorption and emission spectrum of bis-(triphenylphosphine)-dicarbonylnickel(0)

The complex Ni⁰(PPh₃)₂(CO)₂ shows a red photoluminescence (λ_max=650 nm) at r.t. It is suggested that this emission originates from a Ni⁰→PPh₃ metal-to-ligand charge transfer triplet.     

Ultraviolet Absorbing Efficacy and Photostability of Feruloylated Soybean Oil

Feruloylated soy glycerides (FSG) are a natural‐based, ultraviolet (UV) absorbing, antioxidant vegetable oil synthesized from the lipase‐catalyzed transesterification of ethyl ferulate and soybean oil. Commercial broad spectrum UV absorbing formulations contain multiple UV absorbing compounds that absorb UV radiation in specific regions. The most commonly used compounds are avobenzone (AVO, λ_max 356 nm) and octinoxate (ONX, λ_max 310 nm), which absorb primarily ultraviolet A and ultraviolet B radiation, respectively. The FSG chromophore is chemically similar to ONX but has a λ_max of 328 nm, approximately the median λ_max of AVO and ONX. Equimolar mixtures of AVO–ONX and AVO–FSG, 50 μM:50 μM, solutions in ethanol were compared to determine whether FSG was fungible for ONX in total absorbance capacity, photostability when exposed to UV radiation, and broad spectrum absorbance coverage before and after exposure to UV radiation. While it was determined that AVO–FSG mixtures possessed statistically indistinguishable total absorbance capacity compared to AVO–ONX solutions, AVO–FSG possessed slightly better photostability after 4 hours of UV exposure based on 95% confidence interval comparisons from weighted regression equations. Substituting FSG for half of the ONX (e.g., 50 μM:25 μM:25 μM AVO–ONX–FSG) resulted in the best mixture with total absorbance capacity and photostability statistically equal to the AVO–ONX mixtures but with statistically superior broad spectrum UV absorbance compared to AVO–ONX and AVO–FSG mixtures. The natural, vegetable oil‐based FSG can be substituted on an equimolar bases for ONX in mixtures with AVO to produce formulations with similar to superior efficacy.     

BODIPY‐Appended 2‐(2‐Pyridyl)benzimidazole Platinum(II) Catecholates for Mitochondria‐Targeted Photocytotoxicity

Platinum(II) complexes of the type [Pt(L)(cat)] ( 1 and 2 ), in which H₂cat is catechol and L represents two 2‐(2‐pyridyl)benzimidazole ligands with 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) pendants, were synthesized to achieve mitochondria‐targeted photocytotoxicity. The complexes showed strong absorptions in the range λ=510–540 nm. Complex 1 exhibited intense emission at λ=525 nm in 1 % DMSO/water solution (fluorescence quantum yield of 0.06). Nanosecond transient absorption spectral features indicated an enhanced population of the triplet excited state in di‐iodinated complex 2 . The generation of singlet oxygen by complex 2 upon exposure to visible light, as evidenced from experiments with 1,3‐diphenylisobenzofuran, is suitable for photodynamic therapy because of the remarkable photosensitizing ability. The complexes resulted in excellent photocytotoxicity in HaCaT cells (half maximal inhibitory concentration IC₅₀≈3 μm , λ=400–700 nm, light dose=10 J cm^?2), but they remained non‐toxic in the dark (IC₅₀>100 μm ). Confocal microscopy images of 1 and Pt estimation from isolated mitochondria showed colocalization of the complexes in the mitochondria. Complex 2 displayed generation of reactive oxygen species induced by visible light, disruption of the mitochondrial membrane potential, and apoptosis.     

The influence of copper(II) ions on wool photostability in the dry state

It has been hypothesised that the presence of trace metals in wool, notably copper and iron, has an influence on the formation of free radicals under irradiation and thereby affects the photostability of wool and wool products, particularly in the wet state. There has been limited research evaluating the influence of copper ions on wool photodiscoloration. This study examined the relative photodiscoloration of wool bound with varied amounts of copper(II) ions under UVA, UVB and blue light irradiation in the dry state. Total reflectance and visible/near‐infrared absorbance spectra, tryptophan‐type fluorescence (λ_ex = 295 nm, λ_em = 340 nm) and photoinduced chemiluminescence emissions of natural wool and copper(II)‐treated wool were characterised and contrasted. CIELAB colour space, D1925 yellowness and CIE whiteness values measured from irradiated wool samples indicate that wool treated with copper(II) solution at a higher concentration yellowed faster and experienced greater overall colour changes under UVA and UVB irradiation, whereas copper(II)‐treated wool seemed to be more photostable than untreated natural wool under blue light irradiation. It was also observed that binding copper ions to wool resulted in decreased tryptophan‐type fluorescence and photoinduced chemiluminescence emissions relative to untreated natural wool.     

Photoproperties of silver sulfadiazine

Dry silver sulfadiazine (AgSD) is not light sensitive but shows a greenish-blue r.t. photoluminescence at λ_max = 482 nm which is suggested to originate from an IL triplet. In the presence of water AgSD undergoes a partial hydrolysis with the formation of free sulfadiazine (HSD) which has been previously shown to be photoreactive. Moreover, irradiation of an aqueous suspension of AgSD leads also to the photoreduction of Ag⁺ to elemental silver. This photolysis might explain the origin of argyria which can occur when AgSD in contact with human skin is exposed to sun light