Abstract Pressure Sensitive Paints (PSPs) are rapidly revolutionizing aerodynamic wind tunnel testing. PSPs incorporate pressure-sensitive luminescent molecules embedded in oxygen-permeable polymers to image the oxygen concentration, and by extension pressure, on the surfaces of vehicle and engine test models, informing the development of high-performance aerodynamic vehicles. However, current PSPs suffer from high temperature sensitivities, partly due to sensor molecule aggregation, introducing large errors in the measured pressure data. Here, we describe a luminescent Pt(II) porphyrin that is co-polymerized within a fluoroalkyl polymer to produce a PSP (PM1-co-FIB). PM1-co-FIB exhibits a remarkably low temperature sensitivity of 0.3% K–1, a 25% reduction when compared to the current commercial gold standard ISSI UniFIB. The efficacy of PM1-co-FIB PSP was demonstrated in a supersonic wind tunnel test on a flared cone geometry. It demonstrated excellent performance on the hottest (highest pressure error) section of the model, detecting a pressure of 41 kPa, a 7% discrepancy from the calculated value of 44.37 kPa. The PSP aerodynamic data is in excellent agreement with computational fluid dynamics simulations and is able to successfully visualize important aerodynamic phenomena including Görtler vortices.

Abstract There remains much ambiguity regarding the structure of red phosphorus. We report the adsorption and photo-polymerisation of P4 molecules encapsulated in an indium(III)-based metal-organic framework to afford a double-helical chain composite comprising of [P8] units. The similarity between the Raman spectrum of bulk red phosphorus and of the metal-organic framework – (P8)n adduct suggests the presence of such helical chains in the structure of amorphous red phosphorus. This provides crystallographic evidence of the structural building blocks of the red phosphorus allotrope stabilized within the pores of a metal-organic host. The (P8)n inclusion compound is an air-stable semiconductor with a band gap of 2.3 eV, which is relevant for gas detection and photo-catalysis. We demonstrate that this phosphorus adduct demonstrates a 10-fold increase in conversion in the oxidation of methyl orange dye compared with the parent metal-organic framework material.

Pressure-sensitive paints (PSPs) are an optical surface pressure sensor for aerodynamic measurements that operates through the oxygen dependent luminescence of a luminophore molecule. The luminophore has remained relatively consistent over the past 20 years, with platinum(ii)/palladium(ii)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin (Pt/PdTFPP) being popular choices due to their well-known photostability. In this work, NIR-emitting Pt(ii) and Pd(ii) complexes of tetraphenyl tetrabenzoporphyrins and new para CF3 substituted tetraphenyl tetrabenzoporphyrins have been investigated as improved luminophores in PSP formulations for the first time. The red shifted NIR emission spectra of the benzoporphyrins offer a wider and more conveniently placed spectral window than Pt/PdTFPP, creating more of a spectral gap for a secondary temperature-sensitive luminophore to be used in future binary PSPs. The para CF3 substituted Pt(ii) and Pd(ii) benzoporphyrins exhibited substantially increased luminescent brightness over PtTFPP and PdTFPP (5× higher), resulting in signficantly brighter PSP formulations. The benzoporphyrins greatly improved the performance of polystyrene based-PSPs, increasing pressure sensitivity by 20% and decreasing temperature sensitivity by 50%, compared to the current gold standard PtTFPP and PdTFPP.

Photocatalytic synthesis of hydrogen peroxide (H2O2) from oxygen (O2) is a challenging process. Metal-organic framework (MOF) materials are emerging photocatalysts with potential tunable light absorption properties. Herein, we report a rhenium (Re) modified Zr-based MOF, Re10-MFM-67, in which active Re sites are incorporated into MFM-67 by partial replacement of 9,9'-bianthracene-10,10'-dicarboxylic acid (H2L1) with a [(H2L2)ReI(CO)3Cl] (H2L2 = 2,2'-bipyridine-5,5'-dicarboxylic acid) moiety. Re10-MFM-67 (10 refers to the molar percentage content of Re complex within the material) exhibits broadband light absorption with an exceptional rate of formation of H2O2 from O2 of 8.50 mmol gcat-1 h-1 and a record turnover frequency (TOF) of 28.7 h-1 under visible light irradiation (λ > 400 nm). Synchrotron powder X-ray diffraction (SPXRD) and neutron powder diffraction (NPD) confirm the structure of Re10-MFM-67, and together with extended X-ray absorption fine structure (EXAFS) analysis establish the coordination environment and binding of the [ReI(CO)3Cl] moiety within the framework structure. In situ electron paramagnetic resonance (EPR) spectroscopy suggests that photocatalytic H2O2 generation on Re10-MFM-67 occurs via a two-step oxygen reduction reaction (ORR) pathway with the superoxide anion formed as an intermediate. This study promotes the design of MOF-based photocatalysts with conjugated ligands for efficient photosynthesis.

Incorporation of actinide species into iron (oxyhydr)oxides could present an environmentally secure method for preventing the release of actinides over an extended period, as would be the case in a number of radioactively contaminated land situations including surface, near-surface, and subsurface disposal and storage. Uranium is known to incorporate into iron (oxyhydr)oxides, including goethite, in a number of valence states, but the atomistic structures of these processes are unclear. In particular, it is increasingly reported that iron-containing minerals can reductively incorporate and stabilize the +V state of uranium, an oxidation state that is known to be unstable with respect to disproportionation. Here, we use density functional theory within the Periodic Electrostatic Embedded Cluster Method to model U(IV), U(V), and U(VI) incorporation into the pristine and iron-vacancy [010] surface and near-surface region of goethite. Solvated and unsolvated surfaces are studied, and the role of electron transfer from the lattice to uranium ions is explored. Comparisons are made with published X-ray absorption spectroscopic data, and we conclude that, based on the expected conditions for surface and near surface storage sites, both U(VI) and U(V) would incorporate into goethite as it transforms from ferrihydrite, forming two distinct structural types. We find that U(VI) incorporated into goethite may be reduced to U(V), where electron transfer occurs from oxygens surrounding iron vacancies and the incorporated uranium, reducing the U(VI) species to U(V). Both U(VI) and U(V) can incorporate into the surface of goethite with an adjacent iron vacancy, or U(V) can uniquely incorporate into the structure within the near-surface region, containing local but not immediately adjacent iron vacancies for charge compensation. Both of these incorporation schemes are little affected by the presence of a monolayer of surface water, suggesting that incorporation into goethite is a viable method to prevent uranium release into the aqueous surroundings.

The use of pressure-sensitive paints (PSPs), an optical oxygen sensing technique, to visualise and measure the surface pressure on vehicle models in wind tunnel testing is becoming increasingly prevalent. Porphyrins have long been the standard luminophore for PSP formulations, with the majority employing the red-emitting platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin. nIR-emitting luminophores, such as Pt(II) tetraphenyl tetrabenzoporphyrins, possess distinct advantages over visible emitting luminophores. In particular, they have wider spectrally useful ‘windows’, facilitating the insertion of a secondary visible emitting temperature-sensitive luminophore to be used for internal calibration without spectral crosstalk that detrimentally impacts PSP performance. In this work, we explore the effect of changing the loading quantity of an nIR-emitting para-CF3 Pt(II) benzoporphyrin luminophore on the performance of PSP formulations. An optimal luminophore loading of 1.28% wt/wt benzoporphyrin luminophore to polystyrene binder was identified, resulting in a low temperature sensitivity at 100 kPa of 0.61%/K and a large pressure sensitivity at 293 K of 0.740%/kPa. These strong performance metrics, for a polystyrene-based PSP, demonstrate the efficacy of benzoporphyrin luminophores as an attractive luminophore option for the development of a new generation of high-performance PSP formulations that outperform current commercially available ones.

Complexation of U(IV) by encapsulation into the cavity of a 1,4,7-triazacyclonane (tacn) macrocycle functionalized by phosphonated pyridyl arms affords a water-stable and soluble [U(IV)L] complex. The coordination process was monitored by electronic UV-Vis-NIR absorption spectroscopy and the corresponding complex was characterized by 1H-, 13C- and 31P-NMR spectroscopy and by mass spectrometry. Density functional theory (DFT) modeling shows the cation to be embedded into the cavity of the nonadentate ligand, as confirmed by analysis of the paramagnetic contributions of U(IV) on the chemical shifts of the proton nuclei. This effective chelation enabled the observation of a broad NIR emission band centered at 1080 nm observed for the first time in addition to UV-visible emission arising from the U(IV) cation upon electronic excitation in the UV-blue region. The [U(IV)L] complex was shown to be hydrolytically stable for several weeks in aqueous solutions over a broad range of pH values (from 1.6 to 10) under aerobic conditions.

Bis-cycloruthenated complexes (BCRCs) of the type [Ru(N^C)2L2] are proposed to be key reactive intermediates in the Ru(II)-catalyzed directed C-H functionalization of arenes. While the exceptional ground state reactivity of BCRCs toward a number of electrophiles has been explored, their reactivity upon photoexcitation is still unknown. Herein, we report studies on the photoexcitation of BCRCs that establish their capability to access chemically useful excited states. Remarkably, photoexcited BCRCs demonstrate greatly increased reactivity toward the electron transfer processes required for alkyl halide activation, overcoming current limitations of their ground-state reactivity. We have demonstrated this reactivity by expanding upon the current chemical space occupied by Ru-catalyzed C-H functionalization to include ortho-alkylation with epoxides.

Lanthanide (Ln) silylamide chemistry is well-developed, but the corresponding silylphosphide chemistry is immature; there are only ten structurally characterized examples of Ln(II) bis(trimethylsilyl)phosphide complexes to date, and no reported derivatives with bulkier R-groups. Here we report the synthesis of the first f-block bis(triisopropylsilyl)phosphide complexes, [Ln{P(SiiPr3)2}2(THF)x] (1-Ln; Ln = Sm, Eu, x = 3; Ln = Yb, x = 2), by the respective salt metathesis reactions of parent [LnI2(THF)2] with 2 eq. of [Na{P(SiiPr3)2}]n in toluene. Complexes 1-Ln were characterized by a combination of NMR, EPR, ATR-IR, electronic absorption and emission spectroscopies, elemental analysis, SQUID magnetometry and single crystal X-ray diffraction. These data contrast with those obtained for related Ln(II) bis(trimethylsilyl)phosphide complexes due to the bulkier ligands in 1-Ln, and also with Ln(II) bis(triisopropylsilyl)amide complexes due to a combination of longer Ln–P vs. Ln–N bonds and the softer nature of P- vs. N-donor ligands.

We show how the effect of different ligands on the control of the functionalization of unactivated hydrocarbons by visible light excited uranyl catalysts.

Pressure sensitive paints (PSPs) are a powerful optical oxygen sensor technique for measuring the surface pressure distribution upon an aircraft model in wind tunnel testing. Traditional PSPs have relied heavily on platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin due to its reasonable quantum yield of emission, high pressure sensitivity, resistance to photo oxidation, and commercial availability. This work investigates the effect of luminophore chemical structure on PSP performance by altering the degree, substitution pattern, and nature of halogen atom on the phenyl groups of ten different Pt(II) tetraphenyl porphyrins. From this initial screening it was found that platinum(II)-5,10,15,20-tetrakis-(3,5-bis(trifluoromethyl)phenyl)-porphyrin polymer PSPs had a substantially lower temperature sensitivity and a slightly higher pressure sensitivity. Using this new luminophore a Fluoro/Isopropyl/Butyl (FIB) polymer based PSP formulation was optimised whereby it was found that 3.2% w/v of FIB polymer and 800μM concentration of platinum(II)-5,10,15,20-tetrakis-(3,5-bis(trifluoromethyl)phenyl)-porphyrin gave a low temperature sensitivity at 100 kPa for a single component polymer based PSP of 0.22%/K and a relatively high pressure sensitivity at 293K of 0.846, exceeding current commercial PSP performance.

AbstractFormamides are important feedstocks for the manufacture of many fine chemicals. State‐of‐the‐art synthesis of formamides relies on the use of an excess amount of reagents, giving copious waste and thus poor atom‐economy. Here, we report the first example of direct synthesis of N‐formamides by coupling two challenging reactions, namely reductive amination of carbonyl compounds, particularly biomass‐derived aldehydes and ketones, and fixation of CO2 in the presence of H2 over a metal‐organic framework supported ruthenium catalyst, Ru/MFM‐300(Cr). Highly selective production of N‐formamides has been observed for a wide range of carbonyl compounds. Synchrotron X‐ray powder diffraction reveals the presence of strong host‐guest binding interactions via hydrogen bonding and parallel‐displaced π⋅⋅⋅π interactions between the catalyst and adsorbed substrates facilitating the activation of substrates and promoting selectivity to formamides. The use of multifunctional porous catalysts to integrate CO2 utilisation in the synthesis of formamide products will have a significant impact in the sustainable synthesis of feedstock chemicals.

The significant abundance of uranium in radioactive waste inventories worldwide necessitates a thorough understanding of its behavior. In this work, the speciation of uranyl(VI), (UO22+) in a gibbsite system under ambient conditions has been determined as a function of pH by deconvolution and analysis of luminescence spectroscopic data. Uniquely, a combined experimental and statistical approach utilizing time-resolved luminescence spectroscopy and parallel factor analysis (PARAFAC) of excitation emission matrices has been successfully utilized to identify four separate luminescent U(VI) species in the uranyl-gibbsite system for the first time. The speciation of all luminescent U(VI) species in an environmentally relevant system over a pH range of 6-11 is discerned through the analysis of emission fingerprints at low temperature (20 K). Comparison of the deconvoluted luminescence spectra with mineral standards and geochemical models of the system allows the assignment of the luminescent chemical species as metaschoepite, Na-compreignacite, surface adsorbed equivalent to AlO2-UO2(OH) and equivalent to AlO2-UO2(CO3)(2)(4-) complexes, with assignments supported by fitting of extended X-ray absorption fine structure data. The combined spectroscopic techniques in this study show that assignment and quantification of uranyl(VI) species in a sorption system over a large pH range can be accurately achieved using PARAFAC to deconvolute a three way emission spectroscopic data set.

When studying hazardous materials such as spent nuclear fuel (SNF), the minimisation of sample volumes is essential, together with the use of chemically-similar surrogates where possible. For example, the bulk behaviour of urania (UO2) can be mimicked by appropriately-engineered thin films of sufficient thickness, and inactive materials such as ceria (CeO2) can be used to study the effects within radioactive systems used to fuel nuclear fission. However, thin film properties are sensitive to the preparative method, many of which require the use of highly toxic precursors and specialised apparatus (e.g., chemical vapour deposition). To address this, we present the development of a flexible, tuneable, scalable method for the preparation of thin-film CeO2 SIMFUEL models with a thickness of ≈5 μm. The effects of γ irradiation (up to 100 kGy) and dopants including trivalent lanthanides (Ln3+) and simulant ε-particles on the structure and long-term leaching of these systems under SNF storage conditions were explored, alongside the context of this within further work. It was found that the sensitivity of CeO2 films to reduction upon irradiation, particularly in the presence of simulant ε-particles, resulted in increased leaching of Ce (as CeIII), while trivalent lanthanides (Nd3+ and Eu3+) had a minimal effect on Ce leaching.

Whilst lanthanide (Ln) silylamide chemistry is mature, the corresponding silylphosphide chemistry is underdeveloped, with [Sm{P(SiMe3)2}{μ-P(SiMe3)2}3Sm(THF)3] being the sole example of a structurally authenticated Ln(II) silylphosphide complex. Here we expand Ln(II) {P(SiMe3)2} chemistry through the synthesis and characterization of nine novel complexes. The dinuclear ‘ate’ salt-occluded complexes [{Ln[P(SiMe3)2]3(THF)}2(μ-I)K3(THF)] (1-Ln; Ln = Sm, Eu) and polymeric ‘ate’ complex [KYb{P(SiMe3)2}3{μ-K[P(SiMe3)2]}2] (2-Yb) were prepared by the respective salt metathesis reactions of parent [LnI2(THF)2] (Ln = Sm, Eu, Yb) with 2 or 3 eq. of K{P(SiMe3)2} in diethyl ether. The separate treatment of these complexes with either pyridine or 18-crown-6 led to the formation of the mononuclear solvated adducts, trans-[Ln{P(SiMe3)2}2(py)4] (3-Ln; Ln = Sm, Eu, Yb) and [Ln{P(SiMe3)2}2(18-crown-6)] (4-Ln; Ln = Sm, Eu, Yb), with concomitant loss of K{P(SiMe3)2}. The complexes were characterized by a combination of NMR, EPR, ATR-IR, electronic absorption and emission spectroscopies, elemental analysis, SQUID magnetometry, and single crystal X-ray diffraction. We find that these complexes exhibit electronic structures that contrast with those of related Ln(II) bis(trimethylsilyl)amide complexes due to differences in ligand donor atom hardness and ligand steric requirements from Ln–P bonds being longer than Ln–N bonds.

The assessment of trivalent lanthanide yields from the fission of uranium-235 is currently achieved using LN (LaNthanide) resin, di(2-ethylhexyl)orthophosphoric acid immobilized on a solid support. However, coelution of lighter lanthanides into terbium (Tb3+) fractions remains a significant problem in recovery of analytically pure fractions. In order to understand how the separation of trivalent lanthanides and yttrium (Ln(3+)) with LN resin proceeds and how to improve it, their speciation with the organic extractant HDEHP must be fully understood under aqueous conditions. A comprehensive luminescence analysis of aqueous solutions of Ln(3+) in contact with HDEHP, along with infrared spectroscopy, elemental combustion analysis, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and mass spectrometry, was used to indicate that an intermediate species is responsible for the coelution; where similar Ln3+ centers (e.g., Eu3+ and Tb3+) are bridged by the O-P-O moiety of deprotonated HDEHP to form large heteronuclear oligomeric structures with the general formula [Ln2(DEHP)6]( n) . Energy transfer from Tb(3+ )to Eu3+ in this structure confirms that lanthanide centers are within 10 & Aring; and was used to propose that the oligomeric [Ln(2)(DEHP)(6)] (n) structure is formed rather than a dimeric Ln(2)(DEHP)(6 )structure. The effect of this speciation on LN resin column elution is investigated using luminescence spectroscopy, confirming that the oligomeric [Ln(2)(DEHP)(6)]( n )species could disrupt regular elution behavior and cause the problematic bleeding of lighter lanthanides (Sm3+ and Eu3+) into Tb3+ fractions. Resin luminescence measurements were used to propose that the bleeding of the organic extractant HDEHP from its solid support causes the formation of the disruptive oligometallic species.

Radical ipso- substitution offers an alternative to organometallic approaches for biaryl synthesis, but usually requires stoichiometric reagents such as tributyltin hydride. Here, we demonstrate that visible light photoredox catalysis can be used for ipso -biaryl synthesis, via a halogen-atom transfer (XAT) regime. Using amide substrates that promote ipso- over unwanted ortho- addition, we demonstrate smooth biaryl formation with no constraint on the electronic character of the migrating arene ring. The photoreaction can be combined in one operation to achieve a formal arylation of the inert aniline C−N bond.

Since the 1980s, pressure-sensitive paint (PSP) has been used as an optical pressure sensor for measuring surface pressure on aircraft models in wind tunnels. Typically, PSPs have utilized platinum(II)-5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin due to its high pressure sensitivity, phosphorescence lifetime of ∼50 μs, reasonable quantum yield of emission, and resistance to photo-oxidation. This work investigates the photophysics and electronic structure of metal complexes of 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin, namely, Zn(II), Pd(II), and Ir(III), as potentially improved luminophores for polymer-based PSPs. The metal ion was found to preferentially stabilize the a2u MO of the porphyrin with increasing electronegativity, thus blue-shifting absorption/emission maxima and increasing Q-band intensity. The lifetime and quantum yield of emission increased and decreased, respectively, in the order of Pt(II) to Ir(III) to Pd(II), primarily due to the heavy atom effect. The increase in phosphorescence lifetimes resulted in the pressure sensitivity of the PSPs increasing in the order of Pt(II) to Ir(III) to Pd(II). However, the temperature sensitivity at pressures >70 kPa also increased with increasing phosphorescence lifetime. Overall, this work identified that the central metal ion of porphyrin luminophores can be used to tailor the resulting lifetime of the luminophore and therefore heavily influences the pressure and temperature sensitivity of polymer PSP formulations. This new insight into luminophore design can be used to optimize PSPs for a desired application.