UV Absorption Band Research Articles

Ultrafast Decay Dynamics of the 21ππ* Electronic State of N-Methyl-2-pyridone.

The ultrafast decay dynamics of N-methyl-2-pyridone upon excitation in the near-ultraviolet range of 261.5-227.9 nm is investigated using the femtosecond time-resolved photoelectron spectroscopy method. Irradiation at 261.5 nm prepares N-methyl-2-pyridone molecules with high vibrational levels in the 11ππ* state. The radiation-less decay to the ground state via internal conversion is suggested to be the dominant channel for the 11ππ* state with large vibrational excess energy, which is revealed by a lifetime of 1.6 ± 0.2 ps. As the pump wavelength decreases, we found that irradiation at 238.5 and 227.9 nm results in the population of the 21ππ* state. This is in agreement with the assignment of the vapor-phase UV absorption bands of N-methyl-2-pyridone. On the basis of the detailed analysis of our measured time-resolved photoelectron spectra at all pump wavelengths, we conclude that the 21ππ* state has an ultrashort lifetime of 50 ± 10 fs. In addition, the S1(11ππ*) state is subsequently populated via internal conversion and decays over a lifetime of 680-620 fs. The most probable whole deactivation pathway of the 21ππ* state is discussed. This experimental study provides new insights into the excitation energy-dependent decay dynamics of electronically excited N-methyl-2-pyridone.

Effect of doping TiO2 with Fe on the loading of a natural extract

This study explores the relationship between Fe doping in TiO2 nanoparticles and their capacity to load a natural citrus extract. Synthesized TiO2 (T) and TiO2-Fe (TF) nanoparticles were characterized using XRD patterns, N2 physisorption, UV–Vis and FTIR spectroscopy, and electron microscopy. Fe doping induced shifts in X-ray diffraction patterns and broadened absorption bands in UV–Vis spectra, reflecting changes in crystal structure and electronic transitions. BET analysis revealed increased surface area with Fe doping. Loading of the natural citrus extract was confirmed by FTIR. SEM and TEM images displayed slight morphological changes and a reduced nanoparticle size after Fe doping. Finally, Fe doped TiO2 demonstrated an improvement in loading ability with loading values up to 82.4%.

The effect of sonication on the photoluminescence property of carbon quantum dots synthesized by hydrothermal route

Due to their chemical and physical properties, this study focuses on the effect of sonication over carbon quantum dots synthesized by means of hydrothermal route, having as precursor the sour lemon juice from Michoacán, Mexico. The exfoliation was carried out with a sonotrode in times of 1, 2 and 3 hours to provide an explanation over the effect of it on the photoluminescence, where it was found that with times of 1 hour, the PL emission is improved resulting from 261 a.u. to 448 a.u. Other characterizations were carried out to confirm the results obtained in PL, where the average particle size was analyzed by SEM, particle sizes ranging from 5 to 11 nm were observed, with an average size of 7.5 nm and to confirm the carbonaceous material, UV-Vis was performed showing a resolved UV absorption band around 340 nm.

Electronic spectroscopy of gemcitabine and derivatives for possible dual-action photodynamic therapy applications

In this paper, we explore the molecular basis of combining photodynamic therapy (PDT), a light-triggered targeted anticancer therapy, with the traditional chemotherapeutic properties of the well-known cytotoxic agent gemcitabine. A photosensitizer prerequisite is significant absorption of biocompatible light in the visible/near IR range, ideally between 600 and 1000 nm. We use highly accurate multiconfigurational CASSCF/MS-CASPT2/MM and TD-DFT methodologies to determine the absorption properties of a series of gemcitabine derivatives with the goal of red-shifting the UV absorption band toward the visible region and facilitating triplet state population. The choice of the substitutions and, thus, the rational design is based on important biochemical criteria and on derivatives whose synthesis is reported in the literature. The modifications tackled in this paper consist of: (i) substitution of the oxygen atom at O2 position with heavier atoms (O → S and O → Se) to red shift the absorption band and increase the spin–orbit coupling, (ii) addition of a lipophilic chain at the N7 position to enhance transport into cancer cells and slow down gemcitabine metabolism, and (iii) attachment of aromatic systems at C5 position to enhance red shift further. Results indicate that the combination of these three chemical modifications markedly shifts the absorption spectrum toward the 500 nm region and beyond and drastically increases spin–orbit coupling values, two key PDT requirements. The obtained theoretical predictions encourage biological studies to further develop this anticancer approach.

Dual Photo-Responsive Diphenylacetylene Enables PET In-Situ Upcycling with Reverse Enhanced UV-Resistance and Strength.

A novel in situ chemical upcycling strategy for plastic waste is proposed by the customized diphenylacetylene monomer with dual photo-response. That is, diphenylacetylene reactive monomers are in situ inserted into the macromolecular chain of polyethylene terephthalate (PET) plastics/fibers through one-pot transesterification of slight-depolymerization and re-polymerization. On the one hand, the diphenylacetylene group absorbs short-wave high-energy UV rays and then releases long-wave low-energy harmless fluorescence. On the other hand, the UV-induced photo-crosslinking reaction among diphenylacetylene groups produces extended π-conjugated structure, resulting in a red-shift (due to decreased HOMO-LUMO separation) in the UV absorption band and locked crosslink points between PET chains. Therefore, with increasing UV exposure time, the upcycled PET plastics exhibit reverse enhanced UV resistance and mechanical strength (superior to original performance), instead of serious UV-photodegradation and damaged performance. This upcycling strategy at oligomer-scale not only provides a new idea for traditional plastic recycling, but also solves the common problem of gradual degradation of polymer performance during use.

Dual Photo‐Responsive Diphenylacetylene Enables PET In‐Situ Upcycling with Reverse Enhanced UV‐Resistance and Strength

AbstractA novel in situ chemical upcycling strategy for plastic waste is proposed by the customized diphenylacetylene monomer with dual photo‐response. That is, diphenylacetylene reactive monomers are in situ inserted into the macromolecular chain of polyethylene terephthalate (PET) plastics/fibers through one‐pot transesterification of slight‐depolymerization and re‐polymerization. On the one hand, the diphenylacetylene group absorbs short‐wave high‐energy UV rays and then releases long‐wave low‐energy harmless fluorescence. On the other hand, the UV‐induced photo‐crosslinking reaction among diphenylacetylene groups produces extended π‐conjugated structure, resulting in a red‐shift (due to decreased HOMO–LUMO separation) in the UV absorption band and locked crosslink points between PET chains. Therefore, with increasing UV exposure time, the upcycled PET plastics exhibit reverse enhanced UV resistance and mechanical strength (superior to original performance), instead of serious UV‐photodegradation and damaged performance. This upcycling strategy at oligomer‐scale not only provides a new idea for traditional plastic recycling, but also solves the common problem of gradual degradation of polymer performance during use.

The impact of dimethylformamide on the synthesis of graphene quantum dots derived from graphene oxide

Graphene quantum dots (GQDs) have garnered immense interest in recent years due to their unique optical, electrical, and chemical properties, making them promising candidates for various applications in optoelectronics, bioimaging, and sensing. However, enhancing the control over the size, surface chemistry, and optical properties of GQDs remains a significant challenge. In this study, a novel recipe was proposed to successfully synthesize various GQDs via a typical solvothermal process, which has proven to be a versatile and scalable approach. In addition to the main ingredient – graphene oxide suspension, dimethylformamide (DMF) and hydrogen peroxide serving as a cutting agent were added to the reaction mixture. This synthesis method was found to be more promising than the reference one in which DMF was replaced by double distilled water. Through systematic experimentation, we demonstrated that the addition of DMF enables the successful GQD production over a wider range of reaction times; hence, the UV absorption band and photoluminescence properties of GQDs can be better adjusted. The dependence of photoluminescence on the excitation wavelength was observed in the as-prepared materials as they were excited with a range of wavelengths from 360 to 480 nm. The obtained insights not only advance our understanding of GQD synthesis but also open up avenues for tailoring their properties for specific applications.

Dual-Color Lasers in Interlayer-Free Solution Processed Polymeric Bilayer Devices.

Multiwavelength organic lasers have attracted considerable interest in recent years due to the cost efficiency, wide luminescence coverage, and simple processability of organics. In this work, by simply spin coating immiscible polymeric gain media in sequence, dual-wavelength (blue-green or blue-red) amplified spontaneous emission (ASE) was achieved in bilayer devices. The blue emission, water/alcohol-soluble conjugated polyelectrolyte, poly[(9,9-bis(3'-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibromide (PFN-Br), was used as the bottom layer. The commercially available nonpolar solvent soluble polymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and its blend with poly(3-hexylthiophene) (P3HT) were used as the top active layers offering green and red emission, respectively. This novel compact configuration, without interlayers between the two active layers, offers potential for developing various applications. The carefully selected top and bottom layer polymers not only meet the conditions of immiscibility and different emission wavelength range but also have a common absorption band in UV, which allows simultaneous blue-green or blue-red dual-color ASE behaviors observed in the bilayer devices under the same 390 nm laser excitation. By introducing two-dimension (2D) square distributed feedback (DFB) gratings with different periods (300 nm for blue, 330 nm for green, and 390 nm for red) as cavities, single mode blue-green (Eth = 245 μJ cm-2) and blue-red (Eth = 189 μJ cm-2) lasers were achieved by focusing the excitation laser spot on different 2D DFB gratings area. Furthermore, we found it possible to gain sufficient light confinement for red emission along its diagonal direction (Λ ∼424 nm), whereas the 2D DFB gratings offer feedback for blue emission from the 300 nm period along the rectangle direction. Therefore, both blue and red lasers were eventually achieved in the same PFN-Br/F8BT:P3HT bilayer device on the single 2D DFB gratings with a period of 300 nm in this work.

Acetylacetone Photolysis at 280 nm Studied by Velocity-Map Ion Imaging.

The photolysis of acetylacetone (AcAc) has been studied using velocity-map ion imaging with pulsed nanosecond lasers. The enolone tautomer of AcAc (CH3C(O)CH═C(OH)CH3) was excited in the strong UV absorption band by UV pulses at 280 nm, preparing the S2(ππ*) state, and products were probed after a short time delay by single-photon VUV ionization at 118.2 nm. Two-color UV + VUV time-of-flight mass spectra show enhancement of fragments at m/z = 15, 42, 43, 58, and 85 at the lowest UV pulse energies and depletion of the parent ion at m/z = 100. Ion images of the five major fragments are all isotropic, indicating dissociation lifetimes that are long on the timescale of molecular rotation but shorter than the laser pulse duration (<6 ns). The m/z = 15 and 85 fragments have identical momentum distributions with moderate translational energy release, suggesting that they are formed as a neutral product pair and likely via a Norrish type I dissociation of the enolone to form CH3 + C(O)CH═C(OH)CH3 over a barrier on a triplet surface. The m/z = 43 fragment may be tentatively assigned to the alternative Norrish type I pathway that produces CH3CO + CH2C(O)CH3 on S0 following phototautomerization to the diketone, although alternative mechanisms involving dissociative ionization of a larger primary photoproduct cannot be conclusively ruled out. The m/z = 42 and 58 fragments are not momentum-matched and consequently are not formed as a neutral pair via a unimolecular dissociation pathway on S0. They also likely originate from the dissociative ionization of primary photofragments. RRKM calculations suggest that unimolecular dissociation pathways that lead to molecular products on S0 are generally slow, implying an upper-limit lifetime of <46 ns after excitation at 280 nm. Time-dependent measurements suggest that the observed photofragments likely do not arise from dissociative ionization of energized AcAc S0*.

Effect of Sm3+ ions doping on the structural and optical properties, Judd-Ofelt and radiative parameters of ZnS phosphor materials

Undoped ZnS and Sm3+ doped with varying concentration of ZnS phosphor materials were synthesized via low temperature solid state reaction method. The samples were investigated for the influence of different concentrations of Sm3+ ions on their structural and spectroscopic properties. The presence of various absorption bands in UV–Vis–NIR spectra revealed the transition from ground state to different excited states of Sm3+ ions. The Judd-Ofelt (JO) analyses were evaluated to identify the structure and the bonding around the Sm3+ ions. The high value of Ω2 intensity parameter reveals that the site symmetry is lower. The parameters such as radiative transition probabilities, radiative lifetime, branching ratio, stimulated emission cross-sections and the optical gain parameters are also evaluated. The PL spectra shows five high intensity emission bands centered at 567 nm, 590 nm, 619 nm, 641 nm and 667 nm corresponding to 4G5/2→6Hj (j = 5/2, 7/2,9/2, 11/2, 13/2) transitions and showed optimum for concentration at x = 0.03 in Zn(1-x)S. The quantum yield of the prepared optimal phosphor using integrating sphere method was found to be 10.08%. This indicates that the materials synthesized may be favorable for the applications of laser and other optical devices.

Kinetics and spectroscopic characterization of silica nanoparticles formed while etching quartz in hydrofluoric acid

The kinetic regularities of the silica nanoparticles formed during the quartz etching in hydrofluoric acid were explored for the first time. The main drivers for nanoparticle formation, as well as for the etching reaction of quartz, are the concentration of hydrofluoric acid and the ratio of the solid surface area to the liquid volume. Kinetic factors combined with nanoparticle interaction and agglomeration lead to kinetic changes of their concentrations. The proportion of nanoparticles in the weight balance with the dissolved solids decreases significantly and remains in the 0.03% range during quartz etching. XPS analysis of nanoparticles identified elements of Si, O, and F in chemical states such as Si–O, Si-Ox, SiO2, and F–Si. FT-IR reflection also identified the stretching and bending vibration peaks of the Si–O–Si and O–H. The wide fluorescence peak with a maximum at ∼633–650 nm matches the spectrums of known non-bridging oxygen centers ≡Si–O∙. The UV absorption band with maximum in the range of 195–197 nm, detected for nanoparticle samples in liquid, belongs to the silica E’ defect centers ≡Si. In some spots of the deposited nanoparticles Raman peaks are recorded, which is typical for crystal forms of silica. Using AFM, 3D images of nanoparticles deposited on silicon or glass wafers reveal the grain size range of the particles and the feedback between the morphology of the deposited layers and the surface hydrophilicity. The high stability of the quartz etching nanoparticles in hydrofluoric acid explained their structural specificity because they have a surface fluorinated layer consisting of Si–F bonds around the silica grains. The lack of known molybdate-reactive silica inspection methods for the analysis of etching nanoparticles is disclosed. On the basis of the experimental data, new approaches are proposed for the cleaning of quartz parts from particles and for operative inspection of cleanliness.Silica, nanoparticles, etching, quartz, fluorescence, FT-IR, XPS, NP-ICP-MS.

Spectroscopic Properties of Pb2+-Doped BaF2 Crystals

Various concentrations of PbF2-doped BaF2 crystals were grown by the Bridgman method using a shaped graphite heater. The room temperature optical absorption spectra showed two UV absorption bands (labeled A and D), characteristic of the Pb2+ ions. The structure of the bands was analyzed using the Gaussian multi-peak fitting. The distribution of the Pb2+ ions along the crystals and the effective segregation coefficient were studied using the optical absorption method. The obtained effective segregation coefficient was &gt;1. The Pb2+ ions were not uniformly distributed along the samples. High intensity emission bands were observed in the near UV domain and the visible region.

Heterocyclic boronates as colorimetric and chemical sensors for dialkyltin derivatives

The relevance of recognition for diorganotin (IV) species has been increased due to biological and environmental issues. The development of molecules able to carry out the recognition process of diorganotin (IV) compounds by simple analytical techniques is an interesting research topic. This paper describes the synthesis of three heterocyclic boronates obtained by the reaction of one equivalent of 5-formyl-2-furanboronic acid with two equivalents of 2-aminophenol (1), 4‑hydroxy-3-aminobenzoic acid (2) or 4-nitro-2-aminophenol (3). Reactions resulted in a π-conjugated systems by the formation of two new six membered fused heterocycles since the furan ring opening, as corroborated by single X-ray diffraction analysis for compound 1. Compounds 1–3 are green-colored solids with melting points higher than 300 °C. A solvatochromic effect was observed having the absorption band maxima values between 525 and 600 nm. The presence of donor atoms (N, O) in the boronates allow the use as chemical sensors for dialkyltin derivatives (Me2SnO, Bu2SnO, Me2SnCl2, Bu2SnCl2) by UV–Vis and fluorescence techniques. The recognition process for dialkyltin derivates was detected by color changes in solution and even because the presence of a new absorption band in UV–Vis spectra which is shifted to 600 and 621 nm for compounds 1 and 2, respectively. Boronate 2 showed lower Limit Of Detection values (LOD) of 237 nM for Me2SnCl2 and 234 nM for Bu2SnCl2. Less affinity was noticed for trialkyl derivates ((CH3)3SnCl and (CH3)3SnOH).

One-pot synthesis, characterization, photocatalytic activity and biological studies of Co(II), Ni(II) and Cu(II) complexes of a tetraazamacrocyclic Schiff base

Template condensation between pentane-1,5-dial and triethylenetetramine in the presence of divalent metal salts in methanolic solution resulted in mononuclear 15-membered tetraazamacrocyclic Schiff base metal complexes, [M(C11H22N4)X2], where M = Co(II), Ni(II) and Cu(II), X = Cl− and C11H22N4 is the tetradentate macrocyclic ligand. The bonding and overall geometry of the complexes are inferred through elemental analysis, FT-IR, UV–vis, 1H/13C NMR, ESI-mass, molar conductance, magnetic susceptibility and TG measurements. On the basis of the absorption bands in UV–vis spectra and magnetic moment analyses, a six-coordinate octahedral geometry is proposed for all the metal complexes. The formulation of the metal chelates is compatible with the thermal decomposition profiles. Photocatalytic efficiency of the macrocyclic Ni(II) complex was studied using solar water-splitting. The in vitro antimicrobial activity of metal complexes has been tested against certain bacterial and fungal species. The scavenging ability of DPPH free radicals was used to test the antioxidant activity of the complexes. In addition, MTT assay was used to assess the cytotoxicity of Cu(II) chloro complex against L929 mouse fibroblast cell lines.

Influence of Luminescent Properties of Powders on the Fabrication of Scintillation Ceramics by Stereolithography 3D Printing

Luminescent and scintillation ceramic materials with complex shapes, which can be created by stereolithography 3D printing, are of interest for special phosphor and detector applications. Starting powders for such ceramics may possess UV absorption bands; therefore, it is important to study the possible influence of the powders’ luminescent properties on the printing process. This paper deals with complex garnet oxides, Y3Al5O12 and Gd3Al2Ga3O12—well-known hosts for luminescent materials. The photopolymerization rates of slurries based on the luminescent powders produced by various chemical routes are studied, as well as available printing regimes. The slurries containing Ce-doped powders with a broad absorption band in UV have significantly lower photopolymerization rates compared to the undoped ones; a high Ce doping virtually hinders printing with layers thicker than 25–50 μm. Furthermore, the choice of powder synthesis method is shown to influence the printing process. Slurries with Tb-doped powder, with absorption lines at shorter wavelengths, have good photopolymerization activity, close to that of the undoped powder, and can be printed with layer thicknesses of 25–100 μm.

Unusual photophysics of geranic acid deep eutectic solvents.

The photophysics of natural deep eutectic solvents (NADESs) remains unexplored. Here, we report that a class of NADESs aggregates in water, enabling through-space interaction as evidenced by an unusual emission and redshifted UV absorption band. The NADESs enhanced fluorescence excitation and emission of fluorogenic proteins for improved bioimaging.

Catalytic dye degradation by novel phytofabricated silver/zinc oxide composites.

Phytofabrication of the nanoparticles with exotic shape and size is an attractive area where nanostructures with noteworthy physicochemical and optoelectronic properties that can be significantly employed for photocatalytic dye degradation. In this study a medicinal plant, Plumbago auriculata leaf extract (PALE) was used to synthesize zinc oxide particles (ZnOPs) and silver mixed zinc oxide particles (ZnOAg1Ps, ZnOAg10Ps, ZnO10Ag1Ps) by varying the concentration of the metal precursor salts, i.e. zinc acetate and silver nitrate. The PALE showed significantly high concentrations of polyphenols, flavonoids, reducing sugar, starch, citric acid and plumbagin up to 314.3 ± 0.33, 960.0 ± 2.88, 121.3 ± 4.60, 150.3 ± 3.17, 109.4 ± 2.36, and 260.4 ± 8.90μg/ml, respectively which might play an important role for green synthesis and capping of the phytogenic nanoparticles. The resulting particles were polydispersed which were mostly irregular, spherical, hexagonal and rod like in shape. The pristine ZnOPs exhibited a UV absorption band at 352nm which shifted around 370 in the Ag mixed ZnOPs with concomitant appearance of peaks at 560 and 635nm in ZnO10Ag1Ps and ZnOAg1Ps, respectively. The majority of the ZnOPs, ZnOAg1Ps, ZnOAg10Ps, and ZnO10Ag1Ps were 407, 98, 231, and 90nm in size, respectively. Energy dispersive spectra confirmed the elemental composition of the particles while Fourier transform infrared spectra showed the involvement of the peptide and methyl functional groups in the synthesis and capping of the particles. The composites exhibited superior photocatalytic degradation of methylene blue dye, maximum being 95.7% by the ZnOAg10Ps with a rate constant of 0.0463s-1 following a first order kinetic model. The present result clearly highlights that Ag mixed ZnOPs synthesized using Plumbago auriculata leaf extract (PALE) can play a critical role in removal of hazardous dyes from effluents of textile and dye industries. Further expanding the application of these phytofabricated composites will promote a significant complementary and alternative strategy for treating refractory pollutants from wastewater.

Cytotoxic activity and DNA fragmentation study of nano structured assemblies of copper sulfide nanoparticles using single route molecular precursor source of copper

In this paper, we have reported an easy, template free and squashy solution chemistry path was applied to synthesize variegated nanostructured congregation assemblies of copper nanoparticles at room temperature using hydrazinecarbothioamide coordinated Cu(II) complex through a single route molecular precursor source. The parent compounds were heated under microwave irradiation to obtain diversified CuS nanostructures in the shapes of spheres and nanotubes were found to be assemblies of either nanoplates or nanoparticles. The formation of nanostructured CuS nano particles was detailed studied by differing the synthetic conditions such as reaction time, temperature, parent compounds ratio, and the presence of counter ions. The presence of NO3 - and SO4 2- ions as counter ions were found to be suitable for the formation of nanotubes whereas the presence of Clions initiate the formation of spherical nano assemblies of CuS nano material is obtained. The synthesized samples were characterized using various structural, morphological and optical characterization techniques like elemental analysis, FT-IR, UV-Vis, and thermogravimetric analysis/differential thermogravimetric (TGA/DG). Important changes were observed in the FT-IR spectra of the copper complex compared to the FT-IR spectrum of ligand. X-ray diffraction studies confirms the formation of hexagonal crystalline phase of CuS nano particles: Transmission electron microscopy exhibit nanotube like structures with an average particle size of 78nm. Strong UV absorption band at 425nm confirms the formation of good quality CuS nano particles. The microwave irradiation of parent compounds in the presence of nonpolar solvents like DMF, DMSO environment played a significant role in decreasing the reaction time, decreases the possibility of side reactions and proceeds the reaction in the formation of good quality nanoparticles. The SEM analysis of CuS nano particles confirms the agglomerated grain like surface morphology of nanoparticles. All compounds showed the various pharmacological activities like antioxidant, antibacterial activities due to the presence of strong electron withdrawing and electron releasing functional groups are present in molecular precursors. The microwave synthesis of CuS nanostructured assemblies in nonpolar solvent in a proper stoichiometric ratio is an excellent method for preparing highly efficient bio active agents like antibacterial &amp; antioxidant agents which can be considered as a good drug candidate for medicinal chemists in future.

Characteristics of Anode Materials for Nickel Electroforming

This study comprised an investigation of the characteristics of commercial nickel anode materials routinely employed in sulfamate-based electroforming processes. These included examples of sulfur depolarised anodes containing a relatively high sulfur content and those with much lower levels. Electrochemical studies indicate that the sulfur depolarised anodes underwent dissolution in the active region and were capable of sustaining large current densities at low potentials without passivating, and with current efficiencies approaching 100%. In contrast, low-sulfur containing anodes could only sustain low current densities in the active region, and were prone to passivation. These materials could only undergo high rate dissolution in the transpassive region, but this required relatively high anode potentials and was accompanied by various side reactions which lowered the current efficiency. Additional studies were performed to characterise the sulfamate oxidation products which generates a distinct UV absorption band at 245 nm. These species were produced only when low-sulfur content or inert (platinum) anodes were used, and were absent when sulfur depolarised anodes were employed. The principal anode product was azodisulfonate, but trace amounts of other sulfonate species and sulfur-containing anions may also be present.

Moderation of Oxidative Damage on Aromatic Hydrocarbon-Based Polymers

During the operation of aromatic hydrocarbon-based proton exchange membrane fuel cells, formed radical species attack the membrane. The most deleterious radical formed is HO·, both strongly electrophilic and oxidising. Oligomers of α-methylstyrene sulfonates (PAMSS) were used as model compounds. We report on the complex reaction cascade following the oxidative attack on aromatic cores bearing proton conductive sulfonate groups. UV-absorption bands of initial oxidation products indicate the formation of radical adducts and aromatic cation radicals. Subsequently, a transformation associated with an absorbance build-up at 580 nm is observed, presumably also related to aromatic cation radicals. Build-up and decay are significantly accelerated at high ionic strength levels that are also typical in fuel cells. Increased ionic strength causes phase separation: dynamic light scattering experiments indicate particle formation that is dependent both on chain length and on ionic strength. Aromatic cation radicals are known strong oxidants. With a presumed redox potential of E°((PAMSS-580 nm)·+/PAMSS) ∼ 2 V this oxidizing species should react also with mediocre reductants. Here, Mn(II) was oxidised to Mn(III) with rate constants of (5–10) × 106 M−1s−1. Implications for experimental design of kinetics experiments and understanding chemical mechanisms are discussed.