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A mixed valence Tb(III)/Tb(IV) metal-organic framework: Crystal structure, luminescence property and selective detection of naproxen
摘要： A mixed valence terbium metal-organic framework (MOF), [Tb2(HCOO)(clhex)·2H2O)]·2H2O (BUC-68) was obtained from the reaction of 1,2,3,4,5,6-cyclohexanehexacarboxylic acid (H6clhex), formic acid, N,N-dimethylformamide (DMF) and the terbium salt under hydrothermal condition at 140 ℃. The crystallographic analysis revealed that the three-dimensional BUC-68 is composed of two-dimensional [Tb2(clhex)·2H2O)] sheets linked by formic ligand. X-ray photoelectron spectra (XPS) analysis revealed that there were terbium (III) and terbium (IV) presented in BUC-68. Thermogravimetric analysis (TGA) indicated that BUC-68 was stable up to 350 ℃. Photoluminescent measurement showed that BUC-68 displays strong luminescence emission, which was arose from efficient ligand to metal energy transfer transitions. Finally, BUC-68 was utilized to conduct selective detect of naproxen (NPX) and some small organic molecules.
关键词： naproxen,Metal-organic framework,selective detection,luminescence sensor,mixed valence
更新于2025-09-23 15:19:57
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Arylamino-fluorene derivatives: Optically induced electron transfer investigation, redox-controlled modulation of absorption and fluorescence
摘要： A series of biarylaminofluorene-based systems with donor-π-donor (D-π-D) structure have been designed and synthesized in order to study the dependence on the π-conjugated bridge length of the intervalence charge-transfer transitions (IV-CT) and of the electronic coupling between the redox centers. To this purpose cyclic voltammetry, UV/Vis-NIR, fluorescence spectroscopy and computational investigations have been carried out to characterize the electronic structure of the compounds in the neutral as well as in the mono- and dication states. Additionally, a study of related D-π compounds has been performed to elucidate the effect of the interaction between two redox centers. Interestingly it was observed that the mono- and dication species exhibit intense transition bands in the NIR region, in the 10000-15000 cm-1 range, whose intensity depends on the oxidation state and thus it can be reversibly tuned by an applied potential. In a similar way, all compounds show an oxidation state dependent fluorescence which leads to electrofluorochromism. Particularly significant is the mixed valence behavior that provides these systems singular optoelectronic properties, making them excellent active components for electrochromic and electrofluorochromic applications.
关键词： Fluorene,Optically induced electron transfer,Triarylamines,NIR-Electrochromism,Electrofluorochromism,Mixed-Valence
更新于2025-09-16 10:30:52
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Electronic properties of oxidized cyclometalated diiridium complexes: Spin delocalization controlled by the mutual position of the iridium centres
摘要： Four cyclometalated diiridium complexes, with IrCp*Cl (Cp* = η5-C5Me5?) termini bridged by 1,4- and 1,3-bis(p-tolylimino-ethyl)benzene (1, 2), or 1,4- and 1,3-bis(2-pyridyl)benzene (3, 4), were prepared and characterized by nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray diffraction (complexes 1, 2 and 4). The two iridium centres in complexes 1 and 3 are thus bound at the central benzene ring in the para-position (trans-Ir2), while those in complexes 2 and 4 in the meta-position (cis-Ir2). Cyclic voltammograms of all four complexes show two consecutive one-electron oxidations. The potential difference between the two anodic steps in 1 and 3 is distinctly larger compared to 2 and 4. The visible - near-infrared (NIR) - short-wave infrared (SWIR) absorption spectra of trans-Ir2 monocations 1+ and 3+ are markedly different from those of cis-Ir2 monocations 2+ and 4+. Notably, strong near-infrared electronic absorption appears only in the spectra of 1+ and 3+ while 2+ and 4+ absorb only weakly in the NIR-SWIR region. Combined DFT and TD-DFT calculations have revealed that (a) 1+ and 3+ (the diiridium-benzene trans-isomers) display HOSO and LUSO evenly delocalized over both molecule halves, and (b) their electronic absorptions in the NIR-SWIR region are attributed to mixed metal-to-ligand and ligand-to-ligand charge transfers (MLCT and LLCT). In contrast, cis-isomers 2+ and 4+ do not feature this stabilizing π-delocalization but a localized mixed-valence state showing a weak IVCT absorption in the SWIR region.
关键词： Mixed-valence State,Cyclometalated Isomers,Cyclic Voltammetry,Diiridium Complex,Spectroelectrochemistry
更新于2025-09-12 10:27:22
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Site-sensitive X-ray photoelectron spectroscopy of Fe <sub/>3</sub> O <sub/>4</sub> by photoelectron diffraction
摘要： Fe 2p core-level photoelectron spectra of magnetite were measured using soft X-ray and hard X-ray, and its emission angle dependence was investigated. The photoelectron diffraction pattern from different atomic sites differs because the atomic arrangement surrounding each site is different. By selecting the forward-focusing-peak (FFP) directions characteristic to each atomic site and measuring the kinetic energy dependence of the FFP intensities at the Fe 2p core-level range, we succeed in detecting the variation of the peak intensity of Fe 2p core-level spectra at different emission directions. This result, consistent with recent results, suggests that the lower-binding-energy peak of the Fe 2p core-level spectrum may be assigned as the B site component.
关键词： photoelectron diffraction,magnetic materials,mixed valence
更新于2025-09-10 09:29:36
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Designing Long-Range Charge Delocalization from First Principles
摘要： Efficient electronic communication over long distances is a desirable property of molecular wires. Charge delocalization in mixed-valence (MV) compounds where two redox centers are linked by a molecular bridge is a particularly well-controlled instance of such electronic communication, thus lending itself to comparisons between theory and experiment. We study how to achieve and control long-range charge delocalization in cationic organic MV systems by means of Kohn–Sham density functional theory (DFT), and show that a captodative substitution approach recently suggested for molecular conductance (T. Stuyver et al., J. Phys. Chem. C 122, 3194 (2018)) greatly enhances charge delocalization in para-phenylene-based wires. To ensure the adequacy of our DFT methods, we validate different protocols for organic MV systems of different lengths. The BLYP35 hybrid functional combined with a polarizable continuum model, established by Renz and Kaupp, is indeed capable of correctly describing experimentally observed length-dependent charge delocalization, in contrast to the long-range corrected functionals ω-B97X-D and ω-PBE. We also discuss the implications of these results for a first-principles description of the transition between coherent tunneling and incoherent hopping regimes in molecular conductance.
关键词： Charge Delocalization,Molecular Wires,Mixed-Valence Compounds,Quantum Electronic Structure,Density Functional Theory
更新于2025-09-09 09:28:46
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Electronic Coupling and Electron Transfer between Two Mo? Units via meta- and para-Phenylene Bridges
摘要： A series of three Mo2 dimers bridged by a meta-phenylene group has been studied in terms of electronic coupling (EC) and electron transfer (ET) in comparison with the para isomers. Optical analyses on the mixed-valence complexes indicate that by replacing a para-phenylene bridge with a meta one, the EC between the two Mo2 centers is dramatically weakened; consequently, the ET rates (ket) are lowered by 2?3 orders of magnitude. In the para series, the EC parameters (Hab) and ET rates (ket) are greatly affected by O/S atomic alternation of the bridging ligand. However, for the meta analogues, similar EC and ET parameters are obtained, that is, Hab = 300 – 400 cm?1 and ket ～109 s?1. These results suggest that the through-σ bonds and/or through-space coupling channels are in operation as the π conjugation is disabled. DFT calculations reveal that the destructive quantum interference features for the meta series arise from cancellation of two π-conjugated coupling pathways.
关键词： electronic coupling,intervalence transition,metal–metal bond,mixed-valence,quantum interference
更新于2025-09-04 15:30:14