Correlating Pressure‐Induced Emission Modulation with Linker Rotation in a Photoluminescent MOF

Abstract

Conformational changes of linker units in metalorganic frameworks (MOFs) are often responsible for gateopening phenomena in selective gas adsorption and stimuliresponsive optical and electrical sensing behaviour. Herein, we show that pressure-induced bathochromic shifts in both fluorescence emission and UV/Vis absorption spectra of a two-fold interpenetrated Hf MOF, linked by 1,4-phenylenebis(4-ethynylbenzoate) ligands (Hf-peb), are induced by rotation of the central phenyl ring of the linker, from a coplanar arrangement to a twisted, previously unseen conformer. Singlecrystal X-ray diffraction, alongside in situ fluorescence and UV/Vis absorption spectroscopies, measured up to 2.1 GPa in a diamond anvil cell on single crystals, are in excellent agreement, correlating linker rotation with modulation of emission. Topologically isolating the 1,4-phenylene-bis(4-ethynylbenzoate) units within a MOF facilitates concurrent structural and spectroscopic studies in the absence of intermolecular perturbation, allowing characterisation of the luminescence properties of a high-energy, twisted conformation of the previously well-studied chromophore. We expect the unique environment provided by network solids, and the capability of combining crystallographic and spectroscopic analysis, will greatly enhance understanding of luminescent molecules and lead to the development of novel sensors and adsorbents.

Organic luminescent materials: The concentration on aggregates from aggregation‐induced emission

“…Thus, more and more scientists have devoted themselves into the research of it in recent years. [82][83][84][85][86][87][88][89][90][91] Especially, Ruren Xu and coworkers proposed "Towards a new discipline of condensed matter chemistry" in 2018. [82,83] It is believed that after constant exploration, the molecular structure-packing property relationship could be revealed clearly and the adjustment of luminescence property in aggregation state could be easily realized from the source of molecular design.…”

Enhanced proton conductivity in a flexible metal–organic framework promoted by single-crystal-to-single-crystal transformation

“…15,16 Phase transition has been reported to be an effective approach to tune the property of flexible MOFs, 17 and this can be triggered by ligand substitution, 18 guest uptake, 19 or by changes in temperature 20 and/or pressure. 21 However, studies on the impact of single-crystal-to-singlecrystal (SCSC) transformations on proton conductivity in MOFs have been reported rarely. 22,23 We report herein the SCSC transformation via ligand substitution in a nonporous Pb(II)-based MOF, MFM-722(Pb)-DMA, and the enhancement of proton conductivity in the resultant MFM-722(Pb)-H 2 O.…”

Putting the Squeeze on Molecule-Based Magnets: Exploiting Pressure to Develop Magneto-Structural Correlations in Paramagnetic Coordination Compounds

“…One area where the use of pressure has seen a significant rise in popularity is in the study of functional materials where high-pressure diffraction studies performed in conjunction with other high-pressure measurements on the same sample have helped develop structure-property relationships. Supplementary techniques have included high-pressure UV-Vis [10], fluorescence emission [11], conductivity [12], Mossbauer [13] and magnetic measurements. These combined studies have revealed how structural distortions, caused by increasing pressure, have enforced changes in the physical properties of materials.…”

“…These combined studies have revealed how structural distortions, caused by increasing pressure, have enforced changes in the physical properties of materials. Examples include measuring changes in conductivity and band structure in molecular conductors [12], monitoring framework 'breathing effects' on uptake of guest species within porous Metal-Organic Framework materials [14], and how structural changes in encapsulated fluorophores affect emission properties [11]. One area where this approach has made a significant impact is in the field of magnetism.…”

“…The Cu-O-Cu angles are 102.03(13)° in 9, 102.72(6)° and 101.62(6)° in 10, and 97.40(14)° in 11. At ambient pressure, they crystallise in the monoclinic space groups P21/c (9), C2/c(10) and C2/m(11).HP single crystal XRD measurements were performed using petroleum ether as hydrostatic medium[54]. Data were collected at 0.25, 0.70, 1.20 and 2.50 GPa for 9, at 0.21 and 0.90 GPa for 10, and at 0.30, 0.80, 1.53, 2.25, 2.80, 3.50, 4.00, 4.30 and 4.70 GPa for 11.…”