SCSC Transformation and Post-Synthesis Modification of MOFs with Proton Conduction and Ratiometric Fluorescence-Sensing Properties

Abstract

The modification of metal–organic framework (MOF) materials to facilitate their practical applications is an extremely challenging and meaningful topic. In this work, two stepwise modification strategies for MOFs were conducted. First, we have demonstrated a single-crystal-to-single-crystal (SCSC) transformation from a microporous three-dimensional (3D) MOF to a two-dimensional (2D) coordination polymer (CP). The centrosymmetric [Cd­(3-bpdb)­(MeO-ip)] n (1) transforms into a chiral [Cd2(3-bpdb)­(MeO-ip)2(CH3OH)2] n (2), which is triggered by the reaction time with methanol that acts as a structure-directing agent. The conversion relationship of 1 to 2 at different reaction times was studied in detail. Density functional theory (DFT) calculations clearly state that the irreversible formation of 2 is thermodynamically favorable. Intriguingly, 2 exhibits good proton conduction of 1.34 × 10–3 S cm–1 under 363 K and 98% relative humidity (RH) due to unique H-bond network characteristics. To the best of our knowledge, there are very few cases of 3D to 2D SCSC transformation stimulated by reaction time. The results have important implications for understanding the SCSC transformation mechanism and synthetic chemistry. On the other hand, the lanthanide3+-functionalized hybrids (Ln3+-MOF), Ln3+@1, were continuously prepared by incorporating luminescent Ln3+ ions into the structure of 1 through encapsulating post-synthesis modification (PSM). Tb3+@1 exhibits double emission in water and shows visual ratiometric fluorescence behavior for sensing glutamic acid (Glu), tryptophan (Trp), and Al3+, which is more reliable and accurate than single emission. Our work may not only provide new insights into the multiple modification of MOF materials but also promote the practical application of such materials.

Solvent-oriented structural diversity, sequential SCSC and low-temperature transformation in Cd-coordination polymers: unique turn-on–off sensing of Fe3+

“…As mentioned earlier, the flexible conformation of n -BuO-H 2 ip ligands and 3-bpdb is advantageous for the proposed strategy as they can easily respond to the solvent environment. As shown in previous work, 34,35 the presence of alkoxy groups exhibits a certain degree of structural flexibility in the rigid backbone, and increasing the chain length increases the possibility of flexible conformation, resulting in the structural diversity of CPs. The alkoxy chain, like a tadpole, swims around under the stimulation of different solvents to give rise to a number of conformations that direct the self-assembly of CPs (Fig.…”

Breathing Behavior and Superprotonic Conductivity of Two-Dimensional Flexible Metal–Organic Frameworks Tuned with Alkoxy Groups

“…These findings correspond to the results of the proton conduction experiments. The Arrhenius equation calculation shows that at 98% RH, the activation energy ( E a ) values of 1 – 4 are 1.01, 1.07, 0.98, and 0.88, respectively, and those of 1A – 4A are 0.97, 1.38, 1.48, and 1.21 eV, respectively, indicating that proton transport follows the vehicle mechanism (Figure b,c) . Based on the above-mentioned factors, all compounds have a strong humidity dependence, and their hydrogen-bonding networks are mainly derived from external free water molecules.…”

“…The Arrhenius equation calculation shows that at 98% RH, the activation energy (E a ) values of 1− 4 are 1.01, 1.07, 0.98, and 0.88, respectively, and those of 1A− 4A are 0.97, 1.38, 1.48, and 1.21 eV, respectively, indicating that proton transport follows the vehicle mechanism (Figure 6b,c). 46 Based on the above-mentioned factors, all compounds have a strong humidity dependence, and their hydrogenbonding networks are mainly derived from external free water molecules. Then, a large number of water molecules in the channel act as carriers, receiving protons and transmitting them through self-diffusion in the proton-conducting process.…”

A post-synthetically modified Eu@Zn-MOF for ratiometric fluorescence detection of tetracycline in tap water

“…28 By virtue of chemical interactions such as coordination, covalence, ion exchange and so on, post-synthetic methods provide an efficient means of introducing various functional groups into the pores of MOFs. 28–30 Moreover, post-synthetic methods make the construction of Ln-MOFs more facile. 27 In the past decade, a few Ln-MOFs prepared using post-synthetic methods have been reported and utilized for sensing multifarious analytes.…”