Reversible Alteration of CO₂ Adsorption upon Photochemical or Thermal Treatment in a Metal–Organic Framework

Abstract

A metal-organic framework (MOF) for reversible alteration of guest molecule adsorption, here carbon dioxide, upon photochemical or thermal treatment has been discovered. An azobenzene functional group, which can switch its conformation upon light irradiation or heat treatment, has been introduced to the organic linker of a MOF. The resulting MOF adsorbs different amount of CO(2) after UV or heat treatment. This remarkable stimuli-responsive adsorption effect has been demonstrated through experiments.

Direct visualization of a guest-triggered crystal deformation based on a flexible ultramicroporous framework

“…There are two stable conformations with torsion angles of þ 35.8 and -35.8°(stereo isomers) between the pyridyl and phenyl rings, which are separated by an energy barrier of 6.3 kJ mol À 1 located at the coplanar conformation. The relatively shallow potential wells indicate that the ligand conformation may change easily under external stimuli (such as at different temperatures); however, a conformation reversion should hardly occur below room temperature (kT ¼ 2.5 kJ mol À 1 at 300 K) in the absence of more powerful physical (for example, light irritation) or chemical (for example, interaction of other molecules) stimuli [35][36][37][38] . Obviously, such a thermodynamic profile would be suitable for the construction of a temperature-guest-responsive framework.…”

Photochromic Intercalation Compounds

“…Chemical interactions between matrices and photochrmoic dyes have been designed to construct host-guest photochrmoic materials [52][53][54][55]. As a recent example of solid-state photochromic host guest system, which is relevant to the intercalation compouds, a metal-organic framework (MOF; or a porous coordination polymer PCP) with azobenzene group introduced to the organic linker has been developed for reversible change in CO2 uptake upon external stimuli [56]. The positional changes of the dangling benzene group in cubic cavity of a MOF upon reversible trans-to-cis photoisomerization have been a possible reason to the increased and decreased CO2 uptake.…”

Photoactive and Physical Properties of an Azobenzene-Containing Coordination Framework

“…In particular, Zhou et al synthesised a MOF-5-type framework with appended azobenzenes which protruded into the pores. [39] Light dependent gas adsorption studies were undertaken, showing that the amount adsorbed was reliant on whether the cis or trans isomer was dominant in the material. The authors suggested that this difference was due to the pendant azo group blocking and unblocking access to the metal centre, respectively.…”