Self-Healing 2D Anion-Organic Frameworks for Low-Temperature Water Release

Molecular frameworks have recently shown a great potential in atmospheric water harvesting, in which the water release at low temperatures is challenging. Anion-organic frameworks based on anion-coordination chemistry are presented herein to meet this challenge. These frameworks are prepared as tubular single crystals in pure water from the in situ protonation and crystallization of pyridine-terminated triphenylamine derivatives with hydrochloric or hydrobromic acid. They possess a 2D honeycombed porous structure and carry halogen anions confined within 1D hexagonal nanochannels with a modular size of 1.7-2.3 nm. They exhibit a high water uptake of up to 0.87 g g^-1 and a water release onset temperature as low as -90 °C. The water uptake and release induce significant changes in the crystal morphology and absorption and emission properties of these framework crystals, providing a visual indication of their hydration states over a wide temperature range. The kinetics of dehydration at subglacial temperatures is successfully determined by emission spectral shifts. These framework crystals show a high water-stability and can be used for repeated water capture and release thanks to a rapid and robust self-healing capability. This discovery opens opportunities for the design and synthesis of flexible and self-healing frameworks for porosity-related applications.