Computational prediction on photophysical properties of two excited state intramolecular proton transfer (ESIPT) fluorophores bearing the benzothiazole group

In this contribution, the photophysical properties of two excited state intramolecular proton transfer (ESIPT) fluorophores of 2,6-dibenzothiazolyl-4-methylphenol (I) and 2-benzothiazolyl-6-(2-(benzothiazolyl)vinyl)-4-methylphenol (II) were studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods at the PBE0 theoretical level. To probe into the origin of the absorption and emission bands observed experimentally, the absorption and emission spectra of I and II were simulated by the TD-PBE0/6-311 + G(d,p) calculations. In addition, the photo-induced proton enol–keto tautomerization of the two targeted molecules was also explored. The present studies indicate that a good agreement is found between theoretical predictions and experimental data. Moreover, both of these molecules can undergo an ultrafast ESIPT process, which should be responsible for the single proton-transfer tautomer emission.</p

Elucidation of hydrogen-release mechanism from methylamine in the presence of borane, alane, diborane, dialane, and borane–alane

<div><p>The mechanisms of hydrogen release from methylamine with or without borane, alane, diborane, dialane, and borane–alane are theoretically explored. Geometries of stationary points are optimised at the MP2/aug-cc-pVDZ level and energy profiles are refined at the CCSD(T)/aug-cc-pVTZ level based on the second-order Møller–Plesset (MP2) optimised geometries. H₂ elimination is impossible from the unimolecular CH₃NH₂ because of a high energy barrier. The results show that all catalysts can facilitate H₂ loss from CH₃NH₂. However, borane or alane has no real catalytic effect because the H₂ release is not preferred as compared with the B–N or Al–N bond cleavage once a corresponding adduct is formed. The diborane, dialane, and borane–alane will lead to a substantial reduction of energy barrier as a bifunctional catalyst. The similar and distinct points among various catalysts are compared. Hydrogen bond and six-membered ring formation are two crucial factors to decrease the energy barriers.</p></div

Theoretical study on the reactions of CH₃NHNH₂ with ground state O(³P) atom and excited state O(¹D) atom

<p>The reaction mechanisms of methylhydrazine (CH₃NHNH₂) with O(³P) and O(¹D) atoms have been explored theoretically at the MPW1K/6-311+G(d,p), MP2/6-311+G(d,p), MCG3-MPWPW91 (single-point), and CCSD(T)/cc-pVTZ (single-point) levels. The triplet potential energy surface for the reaction of CH₃NHNH₂ with O(³P) includes seven stable isomers and eight transition states. When the O(³P) atom approaches CH₃NHNH₂, the heavy atoms, namely N and C atoms, are the favourable combining points. O(³P) atom attacking the middle-N atom in CH₃NHNH₂ results in the formation of an energy-rich isomer (CH₃NHONH₂) followed by migration of O(³P) atom from middle-N atom to middle-H atom leading to the product P6 (CH₃NNH₂+OH), which is one of the most favourable routes. The estimated major product CH₃NNH₂ is consistent with the experimental measurements. Reaction of O(¹D) + CH₃NHNH₂ presents different features as compared with O(³P) + CH₃NHNH₂. O(¹D) atom will first insert into C–H2, N1–H4, and N2–H5 bonds barrierlessly to form the three adducts, respectively. There are two most favourable paths for O(¹D) + CH₃NHNH₂. One is that the C–N bond cleavage accompanied by a concerted H shift from O atom to N atom (mid-N) leads to the product P_I (CH₂O + NH₂NH₂), and the other is that the N–N bond rupture along with a concerted H shift from O to N (end-N) forms P_IV (CH₃NH₂ + HNO). The similarities and discrepancies between two reactions are discussed.</p

Theoretical Design of Near-Infrared Al³⁺ Fluorescent Probes Based on Salicylaldehyde Acylhydrazone Schiff Base Derivatives

The aim of this paper is to design near-infrared (NIR) Al3+ fluorescent probes based on a Schiff base to extend their applications in biological systems. By combining benzo­[h]­quinoline unit and salicylaldehyde acylhydrazone, we designed two new Schiff base derivatives. According to theoretical simulations on previous experimental Al3+ probes, we obtained the appropriate theoretical approaches to describe the properties of these fluorescent probes. By employing such approaches on our newly designed molecules, it is found that the new molecules have high selectivity toward Al3+ and that their corresponding Al3+ complexes can emit NIR fluorescence. As a result, they are expected to be potential NIR Al3+ fluorescent probes

Catalytic Activity of a Series of Synthesized and Newly Designed Pyridinium-Based Ionic Liquids on the Fixation of Carbon Dioxide: A DFT Investigation

Exploring a high-efficiency catalyst for the coupling reaction of carbon dioxide (CO₂) with epoxide (PO) is still a challenging project. Ionic liquid (IL) is one of the most ideal catalysts since it could catalyze the coupling reaction in a benign environment in the absence of metal and organic solvent. The catalytic activity of a series of pyridinium-based ILs is theoretically investigated. The influences of the nature of cation, methylene chain length, and anion on the catalytic performance are explored. It has been proven that the catalytic activity of pyridinium-based IL is better than that of imidazolium-based and quaternary ammonium-based ILs. Since the properties of IL could be regulated by variation of cation and anion, four new ILs are designed by introduction of the −COOH, −OH, −SO₃H, and −NH₂ functional groups into the traditional pyridinium-based IL, respectively. Subsequently, the catalytic performance of four newly designed functionalized pyridinium-based ILs is compared with that of the traditional pyridinium-based IL. Only the carboxyl-functionalized pyridinium-based IL has better catalytic activity than the traditional pyridinium-based IL. It is expected that the theoretical investigation might provide helpful clues for further experiments

Insight into the Phosphorescent Process of Cyclometalated Ir(III) Complexes: Combination of the Substituents on Primary and Ancillary Ligands Controls the Emission Rule and Quantum Yield

Rare high-efficiency deep blue organometallic phosphors are one of the major roadblocks to develop the white organic light-emitting diodes (OLEDs). In this article, the phosphorescent properties of four potential blue-emitting cyclometalated (C^N) Ir­(III) complexes (two experimental reported and two theoretical novel designed) are investigated by the density functional theory/time-dependent density functional theory (DFT/TDDFT) method to explore the cooperative effect of the electron-withdrawing substituent on the primary ligand associated with different ancillary ligands. The origins of emission are identified by means of DFT and TDDFT calculations including spin–orbit coupling (SOC). The theoretical results indicate that emissions from the higher-lying triplet state also have a contribution. The radiative rate constant (<i>k</i>_r) is quantitatively determined. To further elucidate the phosphorescent decay process, the SOC matrix elements, singlet–triplet splitting energies, and transition dipole moments are calculated to evaluate the radiative process. Both the temperature-independent and temperature-dependent nonradiative decay processes are considered. The calculated results testify that the incorporation of the electron-withdrawing group heptafluoropropyl (<b>HFP</b>) is not insurance to improve the quantum yield. The substituents on the primary ligand should be combined with the suitable ancillary ligand to enhance the quantum yield

Decorating Upconversion Nanoparticles Mediated by Both Active and Inert Shells on NH₂‑MIL-101(Fe) for the Photocatalytic Degradation of Antibiotics and Organic Dyes

Photocatalysis is a promising pathway to degrade pollutants in water. Although numerous photocatalysts have been developed to remove organic dyes in water, the degradation of antibiotics is still a perplexing problem due to their excellent stability. The hybrid photocatalyst upconversion nanoparticle (UCNP)/metal–organic framework (MOF) has been developed with the aim to utilize the full solar light. However, the low upconversion efficiency results in an unsatisfactory photocatalytic activity. A novel core–shell–shell UCNP, NaYF4:Yb/Tm@NaYF4:Yb@NaYF4 (Tm@Yb@Y), is synthesized to increase the upconversion efficiency. Both the active and inert shells are introduced in the UCNPs, which not only are favorable to weaken the surface quenching but also are helpful to prompt the energy transfer back. As a result, the UC emission intensity is greatly improved as compared with Tm or Tm@Yb. Then, Tm@Yb@Y is combined with NH2-MIL101­(Fe) (NMF) to fabricate the novel photocatalyst Tm@Yb@Y/NMF. It exhibits an excellent photocatalytic activity to degrade rhodamine B (RhB), levofloxacin (OFL), and tetracycline hydrochloride (TC). The contribution of near infrared (NIR) light and inert shell on the whole photocatalysis is considered. The possible photodegradation mechanism is proposed according to the photoelectrochemical measurements, free radical and hole trapping experiments, and pump power dependence of upconversion emission intensities. The outstanding performance of Tm@Yb@Y/NMF should be attributed to the synergistic effect including the wider light absorption range, increased UC emission intensity, and feasible electron–hole separation

Hydroxyl-Imidazolium Ionic Liquid-Functionalized MIL-101(Cr): A Bifunctional and Highly Efficient Catalyst for the Conversion of CO₂ to Styrene Carbonate

Considerable attention has been focused on the development of catalysts for the coupling reaction of carbon dioxide (CO2) and epoxides due to the distinct advantages and importance of this reaction. To develop high-performance and easy-to-recycle catalyst is still a hot topic, especially for candidates with excellent activity under moderate conditions. A new heterogeneous catalyst, MIL-101-ImEtOH, is reported by post-synthesis modification, in which 2-(1-imidazol-1-yl) ethanol (Im-EtOH) is immobilized on MIL-101(Cr). In the absence of solvent and co-catalyst, MIL-101-ImEtOH exhibits high activity for the cycloaddition of CO2 and styrene oxide. A 95.6% yield is achieved under 0.5 MPa CO2 pressure and 90 °C by utilization of 50 mg of catalyst for 3 h. Moreover, MIL-101-ImEtOH is easily separated from the catalytic system by simple filtration. To elucidate the influence of hydroxyl group and porous structure on catalysis, other two supported ionic liquids, MIL-101-EtIm and PS-ImEtOH, are prepared and used to catalyze the title reaction under the same conditions. The contribution of each active component is determined by density functional theory along with noncovalent interaction analysis

Insight into the Active Sites of N,P-Codoped Carbon Materials for Electrocatalytic CO₂ Reduction

Doping heteroatoms in carbon materials is a promising method to prepare the robust electrocatalysts for the carbon dioxide reduction reaction (CO2RR), which is beneficial for sustainable energy storage and environmental remediation. However, the obscure recognition of active sites is the obstacle for further development of high-efficiency electrocatalysts, especially for the N,P-codoped carbon materials. Herein, a series of N,P-codoped carbon materials (CNP) is prepared with different N and P contents to explore the relationship between the N/P configuration and the CO2RR activity. As compared with the N-doped carbon materials, the additional P doping is helpful to improve the activity. The optimum N,P-codoped carbon materials (CNP-900) achieve 80.8% CO Faradaic efficiency (FECO) at a mild overpotential of 0.44 V. On the basis of the X-ray photoelectron spectroscopy results, the suitable ratio between pyridinic N and graphitic N and the least P–N content are beneficial for CO2RR. The density functional theory calculations further illustrate that two elementary steps to form *COOH and *CO in CO2RR are determined by the graphitic N and pyridinic N configurations, respectively. The existence of the P–N configuration breaks the equilibrium between graphitic N and pyridinic N to suppress the activity