Versatile and Switchable Responsive Properties of a Lanthanide‐Viologen Metal–Organic Framework

Abstract

Metal–organic frameworks (MOFs) provide intriguing platforms for the design of responsive materials. It is challenging to mobilize as many components as possible of a MOF to collaboratively accomplish multiple responsive properties. Here, reversible photochromism, piezochromism, hydrochromism, ionochromism, and luminescence modulation of an ionic Eu(III) MOF is reported furnished by cationic electron‐deficient viologen units and exchangeable guest anions. Mechanistically, the extraordinarily versatile responsive properties are owed to electron transfer (ET), charge transfer (CT), and energy transfer, involving viologen as electron acceptor, anion as electron donor, luminescing Eu(III) as energy donor, and anion‐viologen CT complex or ET‐generated radical as energy acceptor (luminescence quencher). Moreover, guest anions and waters provide flexible handles to control the ET‐based responsive properties. Water release/reuptake or exchange with organic solvents can switch on/off the response to light, while reversible anion exchange can disenable or awaken the responses to pressure, light, and water release/reuptake. The impacts of water and anions on ET are justified by the high polarity and hydrogen‐bonding capability of water, the different electron donor strength of anions, and the strong I−‐viologen CT interactions. The rich responsive behaviors have great implications for applications such as pressure sensors, iodide detection, and chemical logic gates.

Quadruple Photoresponsive Functionality in a Crystalline Hybrid Material: Photochromism, Photomodulated Fluorescence, Magnetism and Nonlinear Optical Properties

“…Hitherto, most of CHPMs are supported by photodeformable ligands with examples of diarylethylene‐/azo‐derivatives [15–18] or photoresponsive ligands like pyridinium‐derivatives [19–30] . Besides the CHPMs based on photodeformable or photoresponsive ligands, [15–40] the conjugated N ‐heterocycle moieties as potential electron acceptors (EAs) are also desirable units for yielding CHPMs [41–50] . The assembly of various EAs moieties, electron donors (EDs) species, and metal ions generates assorted CHPMs driven by photoinduced electron‐transfer (ET) between EDs and EAs, [41–55] and the resulting CHPMs feature additional fascinating photoresponsive functionality like photomagnetism, photocurrent, sensor for X‐ray, etc [41–55] …”

Metal–organic framework bearing new viologen ligand for ammonia and Cr2O72− sensing

“…), stimulus response materials that exhibit changes in properties such as discoloration or emission characteristics are the basis for many applications in catalysis, sensors, and biomedicine. [1][2][3][4][5][6] Because of its wide application in molecular devices such as optical switches and sensors, it has aroused great interest. Among various materials, metal-organic frameworks (MOFs) composed of inorganic and organic have unlimited diversity and are very responsive materials.…”

“…Or, by using the synergistic effect between these components, the hybrid crystal network can theoretically endow various response characteristics, and become an excellent material with a variety of stimulus response capabilities. 1,[7][8][9][10][11][12][13] Anionic MOFs with a negatively charged skeleton are a subcategory of MOFs and have unique applications in gas adsorption, sensors, uorescent probes, and so on. [14][15][16] 4,4 0 -Bipyridine and its derivatives (viologen and its derivatives) are a typical electron-decient substance with a strong tendency to carry out electron transfer (ET) and induce energy transfer (EnT).…”

“…At the same time, MOFs designed based on viologen have advantages in chemical sensing/switching and other elds, and their response characteristics can be adjusted by the organization of the D-A block. 1,2,14,15,17,[28][29][30][31][32][33][34][35][36] Ammonia (NH 3 ) is an important industrial raw material with a wide range of uses, but it is also a highly toxic chemical. And even at low concentrations, there is a certain degree of toxicity.…”

Decorating Metal Nitrate with a Coplanar Bipyridine Moiety: A Simple and General Method for Fabricating Photochromic Complexes

“…Powerful organic synthesis has brought about a series of corresponding derivatives, which greatly facilitate the development of CHPMs and stimuli‐responsive materials. Besides photodeformable moieties, photoresponsive pyridinium derivatives have also been broadly used to synthesize CHPMs having captivating structures and photoresponsive properties [20–32] …”