Direct liquefying organic cages into porous liquid molecules for enhanced near-infrared photothermal conversion and catalysis

Abstract

The direct liquefaction of molecular cages by incorporating alkyl chains as sterically hindered fluids, without compromising porosity due to self-filling, presents a significant challenge. Here, we demonstrate that transforming hydrophobic amine cages into hydrophilic ammonium cages via quaternization with poly(ethylene glycol) bearing a terminal carboxylic acid produces a series of targeted type I porous liquid molecules featuring a porous ammonium cage as the cation and multiple carboxylate ions as anions on a kilogram scale. The hydrophobic-hydrophilic incompatibility between the cation and anion prevents alkyl chain interpenetration, preserving porosity and liquidity. Notably, photoirradiation induces stable radical generation (lasting over a year) and a red-shift in absorption toward the near-infrared region for photothermal conversion—an unexpected phenomenon in porous liquids. Utilizing this unique property, we further enhance solvent-free photothermal catalytic performance by encapsulating Au clusters within the cage cavities. This study provides new insights into the straightforward synthesis of porous liquids, akin to conventional chemical synthesis of targeted molecules through precise precursor stoichiometry. It also facilitates the extension of their functions and applications from traditional sorption to smart photothermal conversion/catalysis, promising significant advancements in these fields.