Transient Porosity in Densely Packed Crystalline Carbazole–(p‑Diethynylphenylene)–Carbazole Rotors: CO2 and Acetone Sorption Properties

We report for the first time the high sorption properties of a molecular rotor with no permanent voids or channels in its crystal structure. Such crystalline phase originates from THF, DCM, or the irreversible desolvation of entrapped benzene molecules. From these, the benzene in its solvate form acts as rotation stopper, as supported by dynamic characterization using solid-state 2H NMR experiments. In the solvent-free form, the diffusion of small quantities of iodine vapors caused a significant change in the intramolecular rotation, increasing the known activation energy to rotation from 8.5 to 10.6 kcal mol–1. Notably, those results paved the way for the discovery of the high CO2 uptake (201.6 cm3 g–1 at 196 K, under 1 atm) and acetone (5 wt %), a sorption property that was attributed to both, the restriction of the molecular rotation at low temperatures and the flexibility of the molecular axle made of conjugated p-(ethynylphenylene), surrounded by carbazole.

本研究首次报道了一种晶体结构中无永久孔隙或通道的分子转子（molecular rotor）的高吸附性能。该晶相可通过四氢呋喃（THF）、二氯甲烷（DCM）溶剂体系制备，亦可由包封苯分子的不可逆脱溶剂化过程得到。其中，以溶剂化物形式存在的苯可作为旋转阻断剂，该结论得到了固态2H核磁共振（solid-state 2H NMR）动态表征实验的支持。在无溶剂态下，少量碘蒸气的扩散会使分子内旋转发生显著改变，将已知的旋转活化能从8.5 kcal·mol⁻¹提升至10.6 kcal·mol⁻¹。值得注意的是，上述研究结果为该材料优异吸附性能的发现铺平了道路：其在196 K、1 atm条件下的二氧化碳（CO₂）吸附量可达201.6 cm³·g⁻¹，对丙酮的吸附量可达5 wt%；该吸附性能可归因于两点：一是低温下分子旋转受到限制，二是由共轭对-(乙炔基苯撑)构成且被咔唑（carbazole）环绕的分子轴具有柔性。