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Extrinsic Fabry Perot interferometer fiber sensor for simultaneous measurement of hydrazine vapor and temperature
摘要： A novel optical fiber sensor of hydrazine (N2H4) vapor and temperature is proposed and demonstrated. The perylene diimide derivative (TClPDI) is deposited on the enlarged optical fiber end face as sensitive film, and an extrinsic Fabry Perot resonator is formed with fiber bragg grating (FBG) and fiber end face. The film device exhibits high sensitivity and reproducibility to hydrazine vapor with liner concentration dependent characteristic, which owes to the change of refractive index under hydrazine vapor. The enhancement sensitivity and temperature monitoring could be obtained due to the FBG. The results show that a hydrazine vapor sensitivity of 0.01 dB m/ppm, a temperature sensitivity of 9.8 pm/?C could be achieved. In addition, the effect of enlarged fiber end face on the form of TClPDI film was investigated, the sensing mechanism of the film device to hydrazine vapor was studied. The sensor has the advantages of all optical system, tiny, high repeatability, high reliability and two parameters sensing, showing high potential for practical application.
关键词： Tautomerism,Simultaneous measurement,The change of RI,FBG-FP,Two-parameter
更新于2025-11-28 14:23:57
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Synthesis and photochromic properties of some N-phthalimide azo-azomethine dyes. A DFT quantum mechanical calculations on imine-enamine tautomerism and trans-cis photoisomerization
摘要： This paper presents synthesis, photophysical characterization and quantum mechanical calculations of some N-phthalimide azo-azomethine dyes. The dyes were synthesized via azo coupling reaction between 2,4-substituted aromatic anilines and salicylic aldehyde followed by condensation reactions between azo dyes and N-aminophtalimide. Quantum chemical calculations to optimise the molecular geometry and to determine the electron densities of the trans (E) imine ? enamine and the cis (Z) imine ? enamine isomers and their vibrational frequencies have been computed by using DFT at B3LYP/6–31 + G(d,p) level of theory in vacuo. The effect of the used DMF solvent on the molecular structure and bond energies has been determined by using the IEFPCM model. Thermodynamic parameters such as total electronic energy E(RB3LYP), enthalpy H298 (sum of electronic and thermal enthalpies), free Gibbs energy G298 (sum of electronic and thermal free Gibbs energies) and dipole moment μ were computed in order to estimate the ΔE, Δμ, ΔH, ΔG and ΔS values. The NBO analysis was performed in order to understand the intramolecular charge transfer and the energy of resonance stabilization. After molecular geometry optimization, the electronic spectra were obtained by TD-DFT calculations at the above mentioned basis set using the IEFPCM model of DMF as a solvent. The solvatochromic effect of the dyes in four solvents with different polarity has been studied by UV–VIS spectroscopy and compared with the theoretically predicted. The coincidence between measured and calculated spectra is satisfactory. The dynamic photoisomerization experiments were performed in DMF under irradiation with UV light at λ = 365 nm (mostly E → Z) and with VIS light at λ = 400–800 nm (mostly Z → E). The spectra were recorded in the spectral region from 300 to 800 nm at identical sample concentrations of the three dyes and illumination times in order to investigate the photodynamical E → Z → E conversion of the\N_N\chromophore group of the dyes as well as the imine ? enamine tautomerization.
关键词： Tautomerism,DFT calculations,Schiff bases,Azo-azomethine dyes,Photochromism,Trans-cis photoisomerization
更新于2025-09-23 15:21:01
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Photoinduced valence tautomerism of a cobalt-dioxolene complex revealed with femtosecond M-edge XANES
摘要： Cobalt complexes that undergo charge-transfer induced spin-transitions or valence tautomerism from low spin CoIII to high spin (HS) CoII are potential candidates for magneto-optical switches. We use M2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy with 40 fs time resolution to measure the excited-state dynamics of CoIII(Cat-N-SQ)(Cat-N-BQ), where Cat-N-BQ and Cat-N-SQ are the singly and doubly reduced forms of the 2-(2-hydroxy-3,5-di-tert-butylphenyl-imino)-4,6-di-tert-butylcyclohexa-3,5-dienone ligand. The extreme ultraviolet probe pulses, produced using a tabletop high-harmonic generation light source, measure 3p → 3d transitions and are sensitive to the spin and oxidation state of the Co center. Photoexcitation at 525 nm produces a low-spin CoII ligand-to-metal charge transfer state which undergoes intersystem crossing to high-spin CoII in 67 fs. Vibrational cooling from this hot HS CoII state competes on the hundreds-of-fs time scale with back-intersystem crossing to the ground state, with 60% of the population trapped in a cold HS CoII state for 24 ps. Ligand field multiplet simulations accurately reproduce the ground-state spectra and support the excited-state assignments. This work demonstrates the ability of M2,3-edge XANES to measure ultrafast photophysics of molecular Co complexes.
关键词： valence tautomerism,ultrafast spectroscopy,M-edge XANES,Cobalt complexes,high-harmonic generation
更新于2025-09-19 17:13:59
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Homodinuclear {LnIII2} (LnIII = GdIII, TbIII, HoIII, and DyIII) Complexes: Field- Induced SMM Behavior of the DyIII and TbIII Analogues
摘要： A family of four dinuclear complexes, [NHEt3]2[Ln2(μ-NO3)2(NO3)2(HL)2] [Ln = GdIII (1), TbIII (2), HoIII (3), DyIII (4)], were synthesized by the reaction of an enolizable mutidentate Schiff base ligand H3L (H3L = N'-(2-hydroxy-3-methoxy-5-nitrobenzylidene)-2-(hydroxyimino)propanehydrazide) with hydrated lanthanide nitrates in the presence of NEt3. The molecular structure of complexes 1-4 was confirmed by single-crystal XRD analysis. All of the centrosymmetric complexes are dianionic, isostructural and each of the LnIII center is nine-coordinated and adopts a muffin like coordination geometry as indicated by SHAPE analysis. The dynamic magnetization studies revealed that the compounds 2 and 4 are field-induced single-molecule magnets with effective energy barriers, Ueff = 34(2) K (for 2) and 80(3) K (for 4) and pre-exponential factors, τo = 1.1 x 10-8 (for 2) and 1.15 x 10-7(for 4).
关键词： Tautomerism,Lanthanides,Schiff bases,Homodinuclear complexes,Magnetism
更新于2025-09-10 09:29:36