Chemistry

Due to high thermodynamic stability, the direct generation of formic acid by CO₂ hydrogenation is not easy to achieve experimentally. However, when Nakahara and coworkers studied the equilibrium of formic acid reversibly decomposing into CO₂ and H₂, they found that using imidazolium formate ionic liquid as an additive could shift the reaction equilibrium to the formic acid side. Subsequently, imidazolium acetate ionic liquid and imidazolium bicarbonate ionic liquid have also been experimentally proven to be able to be used for CO₂ hydrogenation to directly produce formic acid. In order to investigate the mechanism of action of ionic liquids in the process of CO₂ catalyzed hydrogenation to formic acid, we performed DFT calculations. The results showed that, after the hydrogenation of CO₂ to formic acid, the ionic liquids and formic acid molecules form adducts through hydrogen bonding, and then stabilize the product formic acid. The further use of methyl to replace H at the position of the cation R3 of the ionic liquids can improve the ability of the ionic liquids to stabilize formic acid, which also supports the experimental work of Nakahara and coworkers. In addition, among the three ionic liquids, the imidazolium acetate ionic liquid had the best stabilizing effect on formic acid, and the second best is the imidazolium formate ionic liquid, while the imidazolium bicarbonate ionic liquid has a relatively weak stabilizing ability.

A unified electromagnetic response theory has been formulated in terms of quasi-energy derivatives within the nonrelativistic single-determinant framework. The formalism is applicable to any type of optical response, without restriction to monochromatic fields. Electromagnetic properties are expressed through quasi-energy derivatives, providing a consistent and general description under arbitrary static or dynamic perturbations. Magnetic properties obtained from this framework are inherently gauge-invariant, since a gauge transformation of the electromagnetic potentials corresponds to a unitary phase transformation acting on both the Hamiltonian and molecular orbitals. The present theory thus offers a comprehensive foundation for evaluating (hyper)polarizabilities, (hyper)magnetizabilities, and other related response properties.

In organic solids, the heterogeneous distribution of organic molecules in the solid state gives rise to novel structure–property relationships. Here, we use transmission electron microscopy to investigate the aggregated structure of organic solid of a typical phosphorescent molecule Ir(ppy)₃ at the atomic scale. Through the identification of heavy Ir atoms in the molecular structure, we reveal the existence of organic crystals, clusters and single molecules in the solids. Through electron energy loss spectroscopy, we explore the vibration modes of molecules and lattices in the solids and possible perturbations by excitons induced by electron beam, which could affect the electroluminescent property of the molecules.