Reducing the emission of greenhouse gases, such as CO₂, requires efficient and reusable capture materials. The energy for regenerating sorbents is critical to the cost of CO₂ capture. Here, we design a series of photoswitchable CO₂ capture molecules by grafting Lewis bases, which can covalently bond CO₂, to azo-based backbones that can switch configurations upon light stimulation. The first-principles calculations demonstrate that intramolecular hydrogen bonds are crucial for enlarging the difference of CO₂ binding strengths to the cis and trans isomers. As a result, the CO₂–sorbent interaction can be light-adjusted from strong chemical bonding in one configuration to weak bonding in the other, which may lead to a great energy reduction in sorbent regeneration.

We propose a series of azolium poly(azolyl)borate ionic liquids (ILs) for reversible SO₂ capture. Density functional calculations demonstrate that the designed borate anions can strongly bond to SO₂ at multiple sites with nearly uniform binding energies. Thus, as well as high overall uptakes, the ILs can achieve much higher effective uptakes (the uptake difference between absorption and desorption conditions) than existing SO₂-capture reagents. The larger size of the borate anions, the evenly distributed negative charge among the azolyl rings, and the blocking of the conjugation by the tetrahedral boron concertedly reduce absorbate–absorbate repulsion, which leads to a large disparity among binding sites in other multiple-site SO₂ sorbents.

Boryl radicals have the potential for the development of new molecular entities and for application in new radical reactions. However, the effects of the substituents and coordinating Lewis bases on the reactivity of boryl radicals are not fully understood. By using first-principles methods, we investigated the spin-density distribution and reactivity of a series of boryl radicals with various substituents and Lewis bases. The substituents, along with the Lewis bases, only affect the radical reactivity when an unpaired electron is in the boron p_z orbital, that is, for three-coordinate radicals. We found evidence of synergistic effects between the substituents and the Lewis bases that can substantially broaden the tunability of the reactivity of the boryl radicals. Among Lewis bases, pyridine and imidazol-2-ylidene show a similar capacity for stabilization by delocalizing the spin density. Electron-donating substituents, such as nitrogen, more efficiently stabilize boryl radicals than oxygen and carbon atoms. The reactivity of a boryl radical is always boron based, irrespective of the spin density on boron.