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Polymorphism and Structural Filiations in Five New Organic–Inorganic Hybrid Salts of the Heteroleptic Cationic Iridium(III) Complex and Polyoxometalates
摘要： Five new hybrid compounds ionically associating the phosphorescent heteroleptic cationic iridium(III) complex [IrIII(ppy)2(bpy)]+ ([Ir]+) (ppy = 2-phenylpyridine, bpy = 2,2′-bipyridine) and anionic polyoxometalates (POMs) units have been successfully elaborated, namely, [Ir]2[W6O19]·H2O (m-Ir2W6), [Ir]2[W6O19] (t-Ir2W6-2), [Ir]2[Mo6O19] (t-Ir2Mo6-2), [Ir]4[α-Mo8O26]·4DMF·5H2O (Ir4αMo8DMF), and [Ir]2(HDMA)2[β-Mo8O26]·2DMF·H2O (HDMA+ = dimethylammonium) (Ir2βMo8HDMA). These systems differ by the composition and the topology of the POMs, the [Ir]+/POM ratio, the nature of the other counter-cations, and the presence or not of crystallized solvent molecules. Their crystal structures and their photoluminescent properties have been determined and compared with those of a previously reported series of [Ir]+/POM assemblies revealing polymorphism and structural filiations. The emission properties of the compounds are strongly modulated by the nature of the POM units and the crystal packing of the hybrid frameworks.
关键词： Polyoxometalates,Structural Filiations,Polymorphism,Heteroleptic Cationic Iridium(III) Complex,Organic?Inorganic Hybrid Salts
更新于2025-09-09 09:28:46
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Infrared Investigations of the Neutral-Ionic Phase Transition in TTF-CA and Its Dynamics
摘要： The neutral-ionic phase transition in TTF-CA was investigated by steady-state and time-resolved infrared spectroscopy. We describe the growth of high-quality single crystals and their characterization. Extended theoretical calculations were performed in order to obtain the band structure, the molecular vibrational modes and the optical spectra along all crystallographic axes. The theoretical results are compared to polarization-dependent infrared reflection experiments. The temperature-dependent optical conductivity is discussed in detail. We study the photo-induced phase transition in the vicinity of thermally-induced neutral-ionic transition. The observed temporal dynamics of the photo-induced states is attributed to the random-walk of neutral-ionic domain walls. We simulate the random-walk annihilation process of domain walls on a one-dimensional chain.
关键词： domain-wall motion,neutral-ionic phase transition,steady-state and transient infrared spectroscopy,TTF-CA,charge-transfer salts,characterization,random-walk simulations,light-induced phase transition,vibrational spectroscopy,crystal growth
更新于2025-09-09 09:28:46
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Inorganic Salts and Antimicrobial Photodynamic Therapy: Mechanistic Conundrums?
摘要： We have recently discovered that the photodynamic action of many different photosensitizers (PSs) can be dramatically potentiated by addition of a solution containing a range of different inorganic salts. Most of these studies have centered around antimicrobial photodynamic inactivation that kills Gram-negative and Gram-positive bacteria in suspension. Addition of non-toxic water-soluble salts during illumination can kill up to six additional logs of bacterial cells (one million-fold improvement). The PSs investigated range from those that undergo mainly Type I photochemical mechanisms (electron transfer to produce superoxide, hydrogen peroxide, and hydroxyl radicals), such as phenothiazinium dyes, fullerenes, and titanium dioxide, to those that are mainly Type II (energy transfer to produce singlet oxygen), such as porphyrins, and Rose Bengal. At one extreme of the salts is sodium azide, that quenches singlet oxygen but can produce azide radicals (presumed to be highly reactive) via electron transfer from photoexcited phenothiazinium dyes. Potassium iodide is oxidized to molecular iodine by both Type I and Type II PSs, but may also form reactive iodine species. Potassium bromide is oxidized to hypobromite, but only by titanium dioxide photocatalysis (Type I). Potassium thiocyanate appears to require a mixture of Type I and Type II photochemistry to ?rst produce sul?te, that can then form the sulfur trioxide radical anion. Potassium selenocyanate can react with either Type I or Type II (or indeed with other oxidizing agents) to produce the semi-stable selenocyanogen (SCN)2. Finally, sodium nitrite may react with either Type I or Type II PSs to produce peroxynitrate (again, semi-stable) that can kill bacteria and nitrate tyrosine. Many of these salts (except azide) are non-toxic, and may be clinically applicable.
关键词： potassium thiocyanate,potentiation by inorganic salts,potassium bromide,potassium iodide,sodium azide,antimicrobial photodynamic inactivation,potassium selenocyanate,sodium nitrite
更新于2025-09-09 09:28:46
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Raman Characterization of Phenyl-Derivatives: From Primary Amine to Diazonium Salts
摘要： The objective of the present work is to use Raman spectroscopy for characterizing, the fate of phenyl-derivatives, from phenyl-amines to aryl-diazonium derivatives (ADD). Four ADD were investigated: (i) benzene diazoniumtetrafluoroborate (DS), (ii) 4-decyl benzene diazoniumtetrafluoroborate (DS-C10H21), (iii) 4-carboxybenzene diazoniumtetrafluoroborate (DS-COOH) and (iv) 4-(aminoethyl) benzene diazoniumtetrafluoroborate (DS-(CH2)2NH2). Raman investigation of the above ADD confirmed the existence of an N≡N bond stretching in the range of 2285-2305 cm-1. Moreover, the strong band related to CH in plane-bending and C-N-stretching modes in the 1073-1080 cm-1 range, is a signature of phenyl derivatives stemming from ADD. Furthermore, we analyzed and discuss the H-N-(ring) symmetric stretching modes and the ring-N, as well as the benzene-ring vibrational modes, the C-H related vibrations and the functions in para-position carried by the aromatic ring. The effect of structural changes, the conformational rearrangements from amines to ADD and the influence of the substituent located in the para-position on Raman modes, were examined as well. Finally, Raman experiments supported by Density Functional Theory (DFT) modeling allowed us to determine the crystalline structure of DS-COOH.
关键词： Raman,Diazonium salts,Synthesis and characterization,DFT calculations,Phenyl-amines
更新于2025-09-04 15:30:14
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High‐Temperature Phase Change Material (PCM) Selection for Concentrating Solar Power Tower Applications
摘要： With current concerns about the environmental impact of greenhouse gas emissions, reducing our reliance on fossil fuels has become an ever-growing necessity. A thermal energy storage system that utilizes phase change materials (PCMs) in the form of molten salts, coupled with a concentrating solar power tower plant, is proposed as an effective means of achieving highly efficient and cost competitive power generation on par with traditional fossil fuel–based power. In this study, a set of five selection criteria are applied to a wide range of salt mixtures to determine the best candidates for use as PCMs. The selection criteria include the salt mixture’s melting temperature, latent heat, thermal conductivity, material safety, and cost. A shortlist of 20 salt candidates is made, and differential scanning calorimetry experiments are performed on them to verify the thermal properties of these candidates. A final list of eight salts is then selected as the best PCMs for use in a working temperature range between 500 and 800 °C.
关键词： salt selection,solar thermal power,thermal energy storage,latent heat,molten salts
更新于2025-09-04 15:30:14
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Multi-electron reduction of Wells–Dawson polyoxometalate films onto metallic, semiconducting and dielectric substrates
摘要： The investigation of conditions allowing multi-electron reduction and reoxidation of polyoxometalate (POM) films onto solid substrates is considered an issue of critical importance for their successful incorporation in electronic devices, different types of sensors and catalytic systems. In the present paper, the rich multi-electron redox chemistry of films of Wells–Dawson ammonium salts, namely (NH4)6P2Mo18O62 and (NH4)6P2W18O62, on top of metallic (Al), semiconducting (ITO) and dielectric (SiO2) substrates under ambient conditions is investigated. The respective Keggin heteropolyacids, H3PMo12O40 and H3PW12O40, are also investigated for comparison. On Al substrates, the Wells–Dawson ammonium salts are found to be significantly more reduced (4–6e?) compared to the respective Keggin heteropolyacids (≤2e?), in accordance with their deeper lying lowest unoccupied molecular orbital (LUMO) level. Subsequent thermal treatment in air results in reoxidation of the initially highly reduced POM films. Similar behavior is found on ITO substrates, but in initially less reduced (2–4e?) Wells–Dawson POM films. On the other hand, on SiO2 substrates, the thermal reduction of (NH4)6P2Mo18O62 film is observed and attributed to the thermal oxidation of ammonium counterions by [P2Mo18O62]6? anions. Overall, the multi-electron reduction of Wells–Dawson ammonium salts onto metallic and semiconducting substrates (Al, ITO) is determined by the relative position of the LUMO level of POMs in relation to the Fermi level of the substrate (i.e. substrate work function) and affected in a synergistic way by the presence of ammonium counterions. In contrast, on dielectric substrates (SiO2) the reduction of Wells–Dawson POMs ((NH4)6P2Mo18O62) is attributed only to the oxidation of ammonium counterions.
关键词： Polyoxometalates,Semiconducting substrates,Ammonium counterions,Wells–Dawson ammonium salts,Redox chemistry,Keggin heteropolyacids,Metallic substrates,Dielectric substrates,Thermal treatment,Multi-electron reduction
更新于2025-09-04 15:30:14