Pseudo[<i>n</i>]‑pillar[5]arenes: Synthesis, Structures, and Host–Guest Binding Properties

[1n]­Paracyclophane has been known for nearly 40 years, but its derivatives and properties are understudied in comparison to those of other macrocyclic compounds. By the modification of pillar[5]­arene, we successfully obtained five electron-rich pentagonal macrocycles (pseudo­[n]-pillar­[5]­arenes, n = 1–4) with the decrease of substituted phenylenes one after another, achieving the partial derivatization of [15]­paracyclophane skeleton at its phenylene sites. Pseudo­[n]-pillar­[5]­arenes (P­[n]­P­[5]­s) served as a kind of macrocyclic host to form complexes with various guests, such as dinitriles, dihaloalkanes, and imidazolium salt, in a 1:1 host–guest stoichiometric ratio. The binding constants with the guest gradually reduce along the decrease of substituted phenylene segments from host P­[1]­P­[5] to P­[4]­P­[5]. It is worthy to note that P­[n]­P­[5]­s can adjust their conformations to the “pillar-like” shape effectively when binding with succinonitrile in the solid state

Fast, Ambient Temperature and Pressure Ionothermal Synthesis of Three-Dimensional Covalent Organic Frameworks

Covalent organic frameworks (COFs) are an emerging class of porous crystalline polymers with wide range of potential applications. However, the availability of three-dimensional (3D) COFs is still limited, and their synthesis is confined to the high-temperature solvothermal method. Here, we report for the first time a general and simple strategy to produce a series of 3D ionic liquid (IL)-containing COFs (3D-IL-COFs) by using IL as a green solvent. The syntheses are carried out at ambient temperature and pressure accompanied by a high reaction speed (e.g., only three mins for 3D-IL-COF-1), and the IL can be reused without activity loss. Furthermore, the 3D-IL-COFs show impressive performance in the separation of CO₂/N₂ and CO₂/CH₄. This research thus presents a potential pathway to green large-scale industrial production of COFs

Structural Conjugation Tuning in Covalent Organic Frameworks Boosts Charge Transfer and Photocatalysis Performances

Structural conjugation greatly affects the optical and electronic properties of the COF photocatalyst. Herein, we show that 2D hydrazone COFs with either π-extended biphenyl (BPh–COF) or acetylene (AC–COF) frameworks demonstrated distinct charge transfer and photocatalytic performances. The two COFs show good crystallinity and decent porosity as their frameworks are enforced by intra/interlayers hydrogen bonding. However, computational and experimental data reveal that AC–COF managed broader visible-light absorption and narrower optical bandgaps and performed efficient photoinduced charge separation and transfer in comparison with BPh–COF, meaning that the ethynyl skeleton with enhanced planarity better improves the π-conjugation of the whole structure. As a result, AC–COF exhibited an ideal bandgap for rapid oxidative coupling of amines under visible-light irradiation. Furthermore, taking advantage of its better charge transfer properties, AC–COF demonstrated considerable enhanced product conversion and notable functional tolerance for metallaphotocatalytic C–O cross-coupling of a wide range of both aryl bromides and chlorides with alcohols. More importantly, besides being recoverable, AC–COF showcased the previously inaccessible etherification of dihaloarene. This report shows a facile approach for manipulating the structure–activity relationship and paves the way for the development of a COF photocatalyst for solar-to-chemical energy conversion