化学•材料最新文献

Approaches for evaluating excited state wave functions and energies using diffusion Monte Carlo (DMC) with guiding functions (guided DMC) are discussed. For this work, the guiding functions are functions of a subset of the 3N - 6 coordinates that are needed to describe the structure of the molecule of interest. The DMC wave functions are used to evaluate intensities using two approaches. In the trial wave function approach, the product of the molecular wave function for one of the states involved in the transition and the guiding function for the second state is used to evaluate the matrix elements of the dipole moment. In the descendant weighting approach, descendant weights are used to evaluate the value of the wave function for one of the states involved in the transition at the geometries sampled by the DMC wave function for the second state. The descendant weighting approximation is shown to be more accurate as well as computationally more expensive compared to approximations that are based on various forms of the trial wave function approach. Strategies are explored, which combine results of different forms of the trial wave function approximation to minimize the errors in this approach. The trial wave function and descendant weighting approaches are applied to a study of a harmonic oscillator, where the sensitivity of the calculated energies and intensities to the quality of the trial wave function is explored. The two approaches are also applied to calculations of frequencies and intensities of transitions in water, H₃O₂^-, a four-dimensional (4D) model based on H₃O₂^- and H₅O₂⁺. We also show how comparisons of the results obtained using several forms of the trial wave function approach allow us to explore how couplings among vibrational motions are reflected in the intensities.

Supramolecular polymers (SPs) based on the stacking of hydrogen-bonded rosettes are attracting increasing attention due to their potential applications as soft materials. However, a detailed description of the interactions that give rise to these one-dimensional architectures is still scarce in the literature. In this work, we use molecular dynamics to analyze in aqueous solution the stability of two SPs based on amino triazines (AT) and amino pyrimidines (AP) modified with a hydrophilic chain of succinic acid (-saH). Our results reveal that the AT-based polymers are stable in both their neutral and anionic (succinate -sa-) forms. In contrast, the anionic AP-based polymer is completely dissociated in the presence of sodium cations. While chloride anions can stabilize AT polymers and even induce helical coordination, sodium cations destabilize the AP polymer by penetrating its structure and coordinating with the N atoms, thereby disrupting the hydrogen bonds of the rosettes. On the contrary, the AT-sa- monomers are able to hold back sodium cations due to their extra endocyclic N atom. The side chains are also essential for the formation of these SPs. In summary, we show how non-covalent interactions can be strategically used to control the stability of these systems.

A novel strategy for C-P bond formation has been developed. The reaction employed aromatic carboxylic acids as the source of aromatic groups to couple with three types of P(O)-H₍₂₎ compounds without the need to isolate intermediates, thereby achieving a one-pot construction of carbon-phosphorus bonds. The protocol demonstrated excellent applicability and functional group tolerance, enabling the production of Ar-P(O)R₂ and Ar₂-PPh with moderate to excellent yields.

Photoenols, formed through photoinduced intramolecular H atom abstraction in o-alkyl-substituted arylketones, typically have limited utility as reactive intermediates owing to fast reversion to the starting material. Herein, we introduced an azido group on the o-alkyl substituent to render the photoreaction irreversible. Irradiation of 2-azidomethylbenzophenone (1) in methanol yielded 2-(hydroxy(phenyl)methyl)benzonitrile (2). Laser flash photolysis of 1 revealed the formation of biradical ³Br1 followed by intersystem crossing to photoenols Z-3 (τ ∼ 3.3 μs) and E-3 (τ > 45 μs), both of which reverted to 1. Alternatively, ³Br1 could lose N₂ to form ³Br2 (not detected), which decays to 2. In cryogenic argon matrices, irradiation of 1 yielded nitrene ³1N and 2 but no photoenols, likely because Z-3 regenerated 1. Both ESR spectroscopy and absorption analysis in methyltetrahydrofuran (80 K) confirmed ³1N formation. Upon prolonged irradiation, the absorbance of ³1N decreased, whereas that of 3 remained unchanged and that of 2 increased. Thus, T_K of 1 is proposed to form ³Br1 via H atom abstraction, with subsequent intersystem crossing to 3 competing with the loss of N₂ to generate ³Br2. DFT calculations revealed a small energy gap (∼2 kcal/mol) between the triplet and singlet configurations of Br2, supporting a mechanism in which ³Br2 intersystem crosses to yield 2.

We successfully developed a decatungstate-catalyzed benzylic C(sp³)-H alkylation of sulfonanilides by utilizing the hydrogen bond between the sulfonamide group of the substrates and decatungstate photocatalysts. Using this catalytic system, site-selective C(sp³)-H alkylation was achieved at the benzylic position near the sulfonamide group.