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Influence of Defects in Boron Nitride Nanotubes in the Adsorption of Molecules. Insights from B3LYP-D2* Periodic Simulations
摘要： The adsorption of H2O, NH3 and HCOOH as polar molecules and C6H6 and CH4 as non-polar ones on a series of zig-zag (6,0) single-walled boron nitride nanotubes (BNNTs) both being defect-free (P_BNNT) and containing defects at the nanotube walls has been studied by means of B3LYP-D2* periodic calculations. We focused on defects derived from monovacancies of B (N-rich_BNNT) and N (B-rich_BNNT) atoms and also on Stone-Wales defects (SW_BNNT). The adsorption of polar molecules with defective BNNTs is generally based on dative interactions and H-bonding, and their adsorption energies strongly depend on the type of BNNT. N-rich_BNNT is the most reactive nanotube towards adsorption of polar molecules, as in all cases deprotonation of the polar molecules is spontaneously given upon adsorption. The strength in the adsorption energies is followed by B-rich_BNNT, SW_BNNT and P_BNNT. Adsorption of non-polar molecules is mainly dictated by dispersion interactions, and, accordingly, the adsorption energies are almost constant for a given molecule irrespective of the type of nanotube.
关键词： adsorption,vacancies,periodic simulations,boron nitride nanotubes,DFT,Stone-Wales defect
更新于2025-09-09 09:28:46
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Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions
摘要： Binol quinone methides (BQMs) can be generated from 1,1′-(2,2′-dihydroxy-1,1′-binaphthyl-6,6′-diyl)bis(N,N,N-trimethylmethanamiuium) bromide (BQMP-b) in a 1:1 MeCN:H2O mixed solution via a ground state intramolecular proton transfer (GSIPT), as mentioned in our previously reported studies. Here, the photoreaction of BQMP-b in neutral and basic aqueous solution (pH = 7, 10, 12) was investigated to explore the possible mechanisms and the key intermediates produced in the process of the photoreaction and to examine whether they are different from those in a neutral mild-mixed MeCN:H2O solution. The studies were conducted using femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), and nanosecond time-resolved resonance Raman spectroscopy (ns-TR3) in conjunction with results from density functional theory (DFT) computations. The results showed that BQMP-b was deprotonated initially and produced BQMs species more effectively through an E1bc elimination reaction in a strong basic aqueous condition (pH = 12), which differed from the reaction pathway that took place in the solution with pH = 7 or 10. A related single naphthol ring molecule 1-(6-hydroxynaphthalen-2-yl)-N,N,N-trimethylmethanaminium bromide (QMP-b) that did not contain a second naphthol ring was also investigated. The related reaction mechanisms are elucidated in this work, and it is briefly discussed how the mechanisms vary as a function of aqueous solution pH conditions.
关键词： E1bc elimination reaction,time-resolved resonance Raman,DFT calculation,bifunctional quinone methides
更新于2025-09-09 09:28:46
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Proton-transfer based azides with fluorescence off–on response for detection of hydrogen sulfide. An experimental, theoretical and bioimaging study
摘要： This work describes the synthesis of photoactive proton transfer compounds based on the benzazolic core containing the azide group. The compounds present absorption in the UV region and fluorescence emission in the visible region of the spectra with large Stokes shift due to a phototautomerism in the excited state (ESIPT). The azide location on the benzazolic structure showed to present a noteworthy role on their photophysics leading to fluorescence quenching. A photophysical study was performed in the presence of NaHS to evaluate their application as H2S sensor. The methodology employed was the reduction of azides to amines using NaHS to mimic H2S, resulting in an off–on response fluorescence mechanism. The observed photophysical features were successfully used to explore the azides as fluorescent probes in biological media. In addition, DFT and TD-DFT calculations with CAM-B3LYP/cc-pVDZ and CAM-B3LYP/jun-cc-pVTZ level respectively were performed in order to understand the photophysics features of azide derivatives, where the main interest was investigate fluorescence quenching experimentally observed in the azide derivatives.
关键词： optical sensor,TD-DFT,fluorescence,ESIPT,azides
更新于2025-09-09 09:28:46
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A Combined Experimental and Theoretical Investigation on Organic Cation Dichlorocopper (II): Structural Characterization, Hirshfeld Surface Analysis, Spectroscopic Properties and DFT Calculation
摘要： The (ethylenediamine) dichlorocopper(II) complex, {[Cu(en)]Cl2}n(en:C2H8N2), was synthesized by hydrothermal technique. The X-ray structure of {[Cu(en)]Cl2}n shows that the compound crystallizes as a one dimensional chain with one chlorine that is non-bridging and the other chlorine which is triply bridging. It crystallizes at room temperature in the centrosymmetric space group P21/m. The structure of {Cu(en)Cl2}n was originally reported by Kumara et al. The surrounding copper is best described as distorted octahedral. The crystal structure was stabilized with an extensive network of N-H…Cl classical hydrogen bond interactions. The investigation on that close intermolecular interactions between the molecules via Hirshfeld surface analyses is presented to reveal subtle differences and similarities in the crystal structures. The decomposition of the fingerprint plot area provides a percentage of each intermolecular interaction, allowing for a quantified analysis of close contacts within the crystal. The optimized molecular structure and vibrational spectra were calculated by the Density Functional Theory (DFT) method using the B3LYP function with the LanL2DZ basis set. Good consistency is found between the calculated results and the experimental structure, FT-IR, and FT-Raman spectra. The detailed interpretation of the vibrational modes was carried out. Optical transmission measurements performed on thin films of {[Cu(en)]Cl2}n revealed two absorption bands at 3.64 eV and 1.907 eV. The calculated HOMO-LUMO energies reveal that charge transfer occurs within the molecule.
关键词： Optical absorption,Synthesis hydrothermal,Complex copper (II),Hirchfeld surface analysis,Crystal structure,DFT vibrational assignment
更新于2025-09-09 09:28:46
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[ACS Symposium Series] Raman Spectroscopy in the Undergraduate Curriculum Volume 1305 || Solvent Sensitivity of the ?C≡N Group: A Raman Spectroscopic Study
摘要： The cyano or nitrile group, ?C≡N, exhibits a distinct vibrational mode around the 2100–2300 cm-1 region that is highly sensitive to the solvent polarity, hydrogen bonding interactions, and the electric field around it. In this chapter, the solvent sensitivity of the ?C≡N group was studied using Raman spectroscopy. First, the Raman spectra of ?C≡N-containing samples ranging from acetonitrile to nitrile gloves were contrasted. Second, we give an example where the ?C≡N group had an associated pH dependence due to the groups around it. Lastly, we studied the effect of various solvents on the ?C≡N mode. Raman assignments were verified using DFT-based calculations.
关键词： cyano group,DFT calculations,Raman spectroscopy,nitrile group,solvent sensitivity
更新于2025-09-09 09:28:46
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Investigation of Structure and Dynamics in a Photochromic Molecular Crystal by NMR Crystallography
摘要： A photochromic anil, N-(3,5-di-t-butylsalicylidene)-4-amino-pyridine, has been studied by single-crystal X-ray diffraction, multinuclear magic-angle spinning NMR and first-principles density functional theory (DFT) calculations. Interpretation of the solid-state NMR data on the basis of calculated chemical shifts confirms the structure is primarily composed of molecules in the ground-state enol tautomer, while thermally-activated cis-keto and photoisomerised trans-keto states exist as low-level defects with populations that are too low to detect experimentally. Variable temperature 13C NMR data reveals evidence for solid-state dynamics which is found to be associated with fast rotational motion of t-butyl groups and 180° flips of the pyridine ring, contrasting the time-averaged structure obtained by X-ray diffraction. Comparison of calculated chemical shifts for the full crystal structure and an isolated molecule also reveals evidence for an intermolecular hydrogen-bond involving the pyridine ring and an adjacent imine carbon which facilitates the flipping motion. The DFT calculations also reveal that the molecular conformation in the crystal structure is very close to the energetic minimum for an isolated molecule, indicating that the ring dynamics arise as a result of considerable steric freedom of the pyridine ring and which also allows the molecule to adopt a favourable conformation for photochromism.
关键词： NMR crystallography,photochromic,anil,solid-state NMR,DFT calculations,molecular dynamics
更新于2025-09-09 09:28:46
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X-Ray, IR, NMR, UV-visible spectra and DFT analysis of 5-aryloxy-(1H)-tetrazoles, structure, conformation and tautomerism
摘要： The predominant tautomeric forms of N1–H, N2–H of 5-(2,6-dimethyl- and 5-(2,6-diisopropylphenoxy)-(1H)-tetrazoles were analyzed at B3LYP method using 6-311G(d,p) basis set in the gas phase. The N1–H form of tetrazoles was found to be more stable than N2–H form in both solid and gas phases. Crystal structures of both tetrazoles show an intermolecular H-bond between N1-H and N4 atom of other tetrazole space. The hydrogen bonds between each tautomer of tetrazoles were evaluated at B3LYP/6-311G(d,p) level. The geometrical parameters and spectral data of tetrazoles and their variation were studied in both solid and gas phases.
关键词： 5-(2,6-Diisopropylphenoxy)-(1H)-tetrazole,DFT,NMR,X-ray,H-bond,Rotation barrier
更新于2025-09-09 09:28:46
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Non-linear Optical Response of Triphenylamine Dyes with D-A-π-A Structure
摘要： In this study, we have designed new triphenylamine dyes with D-A-π-A structure and calculated their electro-optical and non-linear properties. Computational techniques were used to study the effect of additional acceptor in π-conjugated systems on absorption spectra and non-linear properties. All the dyes show absorbance in visible region. During theoretical examination polarizability (α), hyperpolarizability (β) and electronic transitions were calculated. Results indicated that the selection of appropriate lengths of conjugated bridges in dye is very important to design high efficiency dyes. This theoretical frame work would be useful to design other organic dyes.
关键词： Hyperpolarizability,Organic dyes,DFT,Polarizability
更新于2025-09-09 09:28:46
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Structure-directing lone pairs: Synthesis and Structural Characterization of SnTiO3
摘要： SnTiO3 was successfully synthesized for the first time in bulk form by soft chemistry. STEM and Rietveld refinement show that SnTiO3 adopts a structure similar to the archetypical ilmenite-type structure, forming a honeycomb lattice of edge-sharing TiO6-octahedra, which are decorated with Sn2+. Due to formation of a van der Waals gap between the individual layers and hence close energetic minima of different stacking types, SnTiO3 forms multiple stacking orders and twinning domains that we describe by systematic DIFFaX-simulations. The structure is governed by the tin lone pairs, which influence the stacking of the layers as well as local distortions observed by EELS and NMR potentially leading to a wide range of applications.
关键词： DFT,van der Waals gap,Rietveld refinement,soft chemistry,STEM,ilmenite-type structure,EELS,SnTiO3,NMR
更新于2025-09-09 09:28:46
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Adsorption properties of the tetragonal P4/nmm WO3 (100) surface toward molecules involved in the hydration of ethylene
摘要： Industrial demand for ethanol has stimulated research on improved catalysts for ethylene hydration. WO3 and other tungsten-based catalysts have been used in direct hydration of ethylene to ethanol, showing high conversion rate and selectivity toward this reaction. By using first-principles calculations based on spin polarized density functional theory, including also dispersion forces, this paper presents the adsorption properties of molecules involved in the ethylene hydration on the tetragonal P4/nmm WO3 (100) surface. The inclusion of dispersion forces, improved our lattice parameters prediction with respect to previous theoretical studies. For the WO3 tetragonal crystal, the (100) surface contains five chemically distinct atoms: a five-fold coordinate W5c, three different types of two-fold binding oxygen O2c, and a single-coordinated oxygen O1c. The energetically favored adsorption sites of water, ethylene, and ethanol (including also hydrogen) are determined here for the first time on this surface. The surface presents high reactivity towards water and ethylene, the single-fold coordinated oxygens stabilize the adsorbed molecules and after adsorption the tungsten atoms take a W6c role. The obtained configurations of the reactants suggest a Rideal-Eley mechanism of the ethylene over adsorbed water. These results reveal the interactions between the selected tetragonal WO3 surface and the molecules involved in the hydration of ethylene, which ultimately determine the reaction mechanism for ethanol production.
关键词： DFT,hydration,tetragonal phase,ethylene,dispersion forces,WO3,tungsten oxide
更新于2025-09-09 09:28:46