18,677 research outputs found

    Building energy-saving potential of a dual-functional solar heating and radiative cooling system

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    Space heating and cooling devices that rely on renewable resources are in demand amid energy crises in parts of the world. However, common renewable space heating and cooling devices are mono-functional. For regions with heating and cooling seasons, using two mono-functional devices might double the installation and maintenance costs, and prolong the payback period. This study proposed a dual-functional renewable heating and cooling device by utilising solar power and nocturnal radiative cooling. The device is a modified solar heating (SH) collector that optimises the nocturnal radiative cooling (RC) to become an SHRC collector. Investigation of the SHRC collector’s performance and energy-saving potential of a building-integrated SHRC collector was conducted using CFD and EnergyPlus. Analysis of the SHRC collector’s performance in various environmental conditions shows that the SHRC collector can reach 42 % thermal efficiency at zero-reduced temperature and > 50 W/m2 of net cooling power. Also, studies on the optimal air duct and air gap height reveal that a 1 cm air duct and 4 cm air gap as the best options for the SHRC collector design. Simulations of the building-integrated SHRC with a collector area of 9.43 m2 for a typical 100 m2 house building demonstrate the multi-seasonal advantage of the SHRC collector, with at least 1.5 kWh more daily savings than the SH and RC collectors in typical winter and summer days. Furthermore, the simulations estimate the annual combined heating and cooling energy savings by the SHRC collector around 32.7 % in Madrid, 25.5 % in Tokyo, and 14.0 % in Isfahan

    Cyclometallated platinum compounds: optical and biological applications

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    [eng] This Doctoral Thesis is focused on the synthesis of cyclometallated platinum compounds with different structural modifications rationally designed specifically for biological or optical applications. Specifically, tridentate [C,N,N’] and [N,C,N] cyclometallated compounds have been synthesised, differing in their oxidation state, the nature of the cyclometallated ligand, with variations in the rigidity and aromaticity, and with a variety of ancillary ligands. Several synthetic methodologies have been employed and the correct formation of the compounds has been checked by a great variety of techniques such as NMR and infrared spectroscopy, mass spectrometry elemental analysis and single crystal X-ray diffraction. Concerning biological applications, several compounds with anticancer properties have been successfully synthesised, obtaining some species with a high efficacy and minimal toxicity studied through cell viability assays. Additionally, several of the designed compounds presented a complete absence of cross-resistance and thanks to additional testing such as cyclic voltammetry, DNA interaction studies and cell-cycle phase distribution experiments, it has been observed that they present mechanisms of action not analogous to those of the clinically approved drugs. Concerning optical applications, the tuning of the structure of the compounds, especially in the cyclometallating ligands, has been key to achieve efficient phosphorescent platinum(II) compounds with various emissive states. Both emission quantum yields and lifetimes have been determined and DFT calculations have allowed a further understanding of the molecules excited states. Additionally, modification of the ancillary ligands, the solvent, the concentration or the presence of an additional metallic cation have been used as a strategy to promote a red-shift in the emission through the formation of aggregates or heterometallic compounds. Finally, one compound has been selected and tested for the preparation of a Light-Emitting Electrochemical Cell (LEEC) obtaining novel results for a platinum-doped device which are competitive with those reported in the literature for other metals and, to the best of our knowledge, the most efficient platinum system used for LEEC applications

    Stable Room-Temperature Phosphorescence from MXene-Derived Carbon Dots: Ultralong Afterglow Emission without an External Matrix

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    Herein, we synthesized highly defined carbon dots (CDs) from two-dimensional delaminated MXene through a solution-based acid etching method. The as-synthesized CDs show blue fluorescence emission in the solution phase upon neutralization with excess alkali. However, after solidification, the solid powder of CDs shows strong bright green room-temperature phosphorescence/afterglow emission for up to 5 s without using any further external matrix. The fundamental photophysical properties of the CDs are further correlated with the structural and elemental features. It suggests that the rigidity of the surface emissive states due to the slow modification of the exterior surface of CDs facilitates the afterglow emission. Temperature-dependent photoluminescence study and the systematic interconversion between room-temperature phosphorescence and prompt fluorescence depict the possible thermally activated delayed fluorescence at high temperatures. It is further correlated with the low-temperature phosphorescence studies (up to 90 K). The solid powder of CDs has been further utilized directly as a sustainable smart material for anticounterfeiting and information protection applications

    A fluorene-bridged double carbonyl/amine multiresonant thermally activated delayed fluorescence emitter for efficient green OLEDs

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    S. W. thanks the China Scholarship Council (201906250199) for support. D.S. acknowledges support from the Royal Academy of Engineering Enterprise Fellowship (EF2122-13106). E. Z.-C. thanks the Engineering and Physical Sciences Research Council (EP/W015137/1, EP/W007517) for support. X.-H. Z. acknowledges support from the National Natural Science Foundation of China (Grant No. 52130304, 51821002) and the Collaborative Innovation Center of Suzhou Nano Science & Technology.Herein, we report a fluorene-bridged double carbonyl/amine-based MR TADF emitter DDiKTa-F, formed by locking the conformation of the previously reported compound DDiKTa. Using this strategy, DDiKTa-F exhibited narrower, brighter, and red-shifted emission. The OLEDs with DDiKTa-F emitted at 493 nm and showed an EQEmax of 15.3% with an efficiency roll-off of 35% at 100 cd m−2.Publisher PDFPeer reviewe

    Influence of the Nature of Aminoalcohol on ZnO Films Formed by Sol-Gel Methods

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    Here we present comparative studies of: (i) the formation of ZnO thin films via the sol-gel method using zinc acetate dihydrate (ZAD), 2-methoxyethanol (ME) as solvent, and the aminoalcohols (AA): ethanolamine, (S)-(+)-2-amino-1-propanol, (S)-(+)-2-amino-3-methyl-1-butanol, 2-aminophenol, and aminobenzyl alcohol, and (ii) elemental analyses, infrared spectroscopy, X-ray diffraction, scanning electron microscopy, absorption and emission spectra of films obtained after deposition by drop coating on glass surface, and thermal treatments at 300, 400, 500 and 600 â—¦C. The results obtained provide conclusive evidences of the influence of the AA used (aliphatic vs. aromatic) on the ink stability (prior to deposition), and on the composition, structures, morphologies, and properties of films after calcination, in particular, those due to the different substituents, H, Me, or iPr, and to the presence or the absence of a -CH2- unit. Aliphatic films, more stable and purer than aromatic ones, contained the ZnO wurtzite form for all annealing temperatures, while the cubic sphalerite (zinc-blende) form was also detected after using aromatic AAs. Films having frayed fibers or quartered layers or uniform yarns evolved to 'neuron-like' patterns. UV and photoluminescence studies revealed that these AAs also affect the optical band gap, the structural defects, and photo-optical properties of the films

    Cyclometallated platinum compounds: optical and biological applications

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    Programa de Doctorat en Química Orgànica[eng] This Doctoral Thesis is focused on the synthesis of cyclometallated platinum compounds with different structural modifications rationally designed specifically for biological or optical applications. Specifically, tridentate [C,N,N’] and [N,C,N] cyclometallated compounds have been synthesised, differing in their oxidation state, the nature of the cyclometallated ligand, with variations in the rigidity and aromaticity, and with a variety of ancillary ligands. Several synthetic methodologies have been employed and the correct formation of the compounds has been checked by a great variety of techniques such as NMR and infrared spectroscopy, mass spectrometry elemental analysis and single crystal X-ray diffraction. Concerning biological applications, several compounds with anticancer properties have been successfully synthesised, obtaining some species with a high efficacy and minimal toxicity studied through cell viability assays. Additionally, several of the designed compounds presented a complete absence of cross-resistance and thanks to additional testing such as cyclic voltammetry, DNA interaction studies and cell-cycle phase distribution experiments, it has been observed that they present mechanisms of action not analogous to those of the clinically approved drugs. Concerning optical applications, the tuning of the structure of the compounds, especially in the cyclometallating ligands, has been key to achieve efficient phosphorescent platinum(II) compounds with various emissive states. Both emission quantum yields and lifetimes have been determined and DFT calculations have allowed a further understanding of the molecules excited states. Additionally, modification of the ancillary ligands, the solvent, the concentration or the presence of an additional metallic cation have been used as a strategy to promote a red-shift in the emission through the formation of aggregates or heterometallic compounds. Finally, one compound has been selected and tested for the preparation of a Light-Emitting Electrochemical Cell (LEEC) obtaining novel results for a platinum-doped device which are competitive with those reported in the literature for other metals and, to the best of our knowledge, the most efficient platinum system used for LEEC applications.[cat] Aquesta Tesi Doctoral està centrada en la síntesi de compostos ciclometal·lats de platí amb diferents modificacions estructurals dissenyades racionalment per dur a terme aplicacions biològiques o òptiques. Específicament, s’han sintetitzat compostos ciclometal·lats tridentats [C,N,N’] i [N,C,N] que es diferencien en el seu estat d’oxidació, naturalesa del lligand ciclometal·lat, amb variacions en la rigidesa i l’aromaticitat, i amb una varietat de lligands auxiliars. S’han utilitzat diferents metodologies sintètiques i s’ha comprovat la correcta formació dels compostos amb una gran varietat de tècniques com l’espectroscòpia RMN i infraroja, l’espectrometria de masses, l’anàlisi elemental i la difracció de raigs-X de monocristall. Quant a les aplicacions biològiques, s’han sintetitzat amb èxit diversos compostos amb propietats anticancerígenes, obtenint algunes espècies amb eficàcia elevada i amb toxicitat mínima que han estat estudiades a través d’assajos de viabilitat en cèl·lules. A més, diversos compostos dels que s’han sintetitzat van presentar una absència completa de resistència entrecreuada i gràcies a proves addicionals com la voltametria cíclica, estudis de la interacció amb l’ADN i experiments de distribució a les fases del cicle cel·lular, s’ha observat que presenten mecanismes no anàlegs als dels fàrmacs clínicament aprovats. Quant a les aplicacions òptiques, l’afinació de l’estructura dels compostos, especialment en el lligand ciclometal·lat, ha estat clau per aconseguir compostos de platí(II) amb una fosforescència eficient i amb diversos estats emissius. S’han determinat els rendiments quàntics i temps de vida d’emissió i els càlculs DFT han permès un coneixement més detallat dels estats excitats de les molècules. A més, la modificació dels lligands auxiliars, el dissolvent, la concentració o la presència d’un catió metàl·lic addicional, s’han utilitzat com a estratègia per promoure un desplaçament cap al vermell en l’emissió a través de la formació d’agregats o compostos heterometàl·lics. Finalment, s’ha seleccionat un compost per la preparació de cel·les electroquímiques emissores de llum (LEECs) obtenint nous resultats per un dispositiu dopat amb platí que són competitius amb els resultats descrits a la bibliografia per altres metalls i, dins del nostre coneixement, el sistema de platí més eficient utilitzat per la seva aplicació en LEECs

    Turn–on fluorescent sensor for the detection of periodate anion following photochemical synthesis of nitrogen and sulphur co–doped carbon dots from vegetables

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    In this work, a novel one–step ‘bottom–up’ synthetic approach is described for obtaining highly fluorescent nitrogen (N) and sulphur (S) co–doped carbon dots (CDs) following photochemical oxidation of carbohydrates naturally occurring in vegetables. N and S co–doping allows more active sites in the CDs surface resulting in an enhancement of their luminescent properties. Among the 18 vegetables studied as green precursors of CDs, those rich in proteins and glucosinolates (natural S–linked glucosides), such as cruciferous vegetables (Brassicaceae family), i.e. broccoli, cauliflower and Romanesco, facilitate an efficient N and S co–doping of the CDs during the photochemical reaction without the need for further post–synthetic treatments. A comprehensive characterization of CDs obtained from broccoli was performed by transmission electron microscopy, elemental analysis, X–ray fluorescence (total reflection), UV–Vis absorption and Fourier transform–infrared spectroscopy. Quantum yields and fluorescence up–conversion properties were also investigated. Monodisperse CDs (∼8 nm average size) with up–conversion fluorescence properties and a quantum yield (QY) of 22% are obtained. More importantly, a dramatic increase in the CDs fluorescence (turn–on) is observed when the highly oxidant periodate anion (IO4−) is added to the reaction medium, which allowed us to construct a sensitive and selective fluorescent assay for the detection of periodate anion in wastewater samples. The detection limit was 19 μM IO4− and the repeatability expressed as the relative standard deviation was 3.2% (N = 5)Ministerio de Economía y Competitividad | Ref. CTQ2015–68146–

    Exploring transition metal catalysis in water for <i>in vivo </i>applications

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    Transition metal catalysis proves a powerful tool to achieve otherwise synthetically challenging, or even impossible, transformations with (high) selectivity and is therefore employed in various areas of chemistry. Recently, transition metal-catalysed reactions have been successfully performed in cells (in vitro) and living systems (in vivo). The achievements made thus far reveal the potential of transition metal catalysis and its applications in such biological settings. Interestingly, the scope is limited compared to the breadth of transition metal-catalysed reactions that have been unlocked for synthetic applications. Translating transition metal-catalysed reactions from flasks to cells is non-trivial as the conditions in cells are fairly different compared to the highly controlled and adaptable conditions achieved in a flask. The development of catalytic systems for future applications in vivo therefore proceeds through many steps, starting with evaluating their reactivity, selectivity, and stability in water and under biologically relevant and biomimetic conditions. By exploring transition metal-catalysed reactions in water for in vivo applications, this dissertation has contributed to the subfield of bioorthogonal chemistry devoted to complementing Nature’s repertoire of reactions. Our studies have revealed the challenges associated with the performance of transition metal catalysis in aqueous media and how a detailed understanding of a catalytic system can address them. Apart from these fundamental studies, we have performed explorative studies under biologically relevant and biomimetic conditions in the context of intracellular drug synthesis. Moreover, we have developed a new and compatible protocol that enables detailed kinetic studies in complex reaction media, comparable to the cellular environment, to facilitate the translation of transition metal catalysis from flasks to cells

    Luminescent behavior of Zn(II) and Mn(II) halide derivatives of 4-phenyldinaphtho[2,1-d: 1′,2′-f][1,3,2]dioxaphosphepine 4-oxide and single-crystal X-ray structure determination of the ligand

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    The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1′-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr2 afforded complexes having the general formula [ZnBr2{O=PPh(BINOL)}2] that showed intense fluorescence centered in the near-UV region rationalized on the basis of TD-DFT calculations. The corresponding Mn(II) complexes with the general formula [MnX2{O=PPh(BINOL)}2] (X = Cl, Br) exhibited dual emission upon excitation with UV light, with the relative intensity of the bands dependent upon the choice of the halide. The highest energy transition is comparable with that of the Zn(II) complex, while the lowest energy emission falls in the red region of the spectrum and is characterized by lifetimes in the hundreds of microseconds range. Although the emission at lower energy can also be achieved by direct excitation of the metal center, the luminescence decay curves suggest that the band in the red range is possibly derived from BINOL-centered excited states populated by intersystem crossing

    It\u27s not just the size that matters: crystal engineering of lanthanide-based coordination polymers

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    Synthesis and characterization of Lewis base free coordination polymers of selected lanthanides are presented. For this purpose, the substituted CotTIPS^{TIPS} ligand (CotTIPS^{TIPS} = 1,4-bis-triisopropylsilyl-cyclo-octatetraendiide) was used to synthesize homoleptic, anionic multidecker compounds of the type [K{LnIII^{III}(ɳ8^8-CotTIPS^{TIPS})2_2}]n_n. Depending on the solvent used for crystallization and the ionic radii of the lanthanide cations, three different categories of one-dimensional heterobimetallic coordination polymers were obtained in the solid state. For the early lanthanides La and Ce a unique helical conformation was obtained by crystallization from toluene, while the ionic radius of Pr seems to be a turning point towards the crystallization of zigzag polymers. For Er a third structural motif, a trapezoidal wave polymer was observed. Additionally, the zigzag polymer for all compounds could be obtained by changing the solvent from toluene to Et2_2O, reavealing a correlation between solid-state structure and ionic radii as well as solvent. While photoluminescence (PL) properties of Cot-lanthanide compounds are scarce, the La complexes show ligand centered green luminescence, whereas the Ce complexes reveal deep red emission origin from d–f transitions. The Er-compounds are single-molecule magnets, in which the magnetic relaxation of each Er ion occurs isolated from its neighbors at temperatures above 10 K, while below 9 K a strong antiferromagnetic coupling between the Er ions was seen
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