A Light‐Responsive Metal–Organic Framework Hybrid Membrane with High On/Off Photoswitchable Proton Conductivity

Abstract

Mimicking biological proton pumps to achieve stimuli-responsive protonic solids has long been of great interest for their diverse applications in fuel cells, chemical sensors, and bio-electronic devices. Now, dynamic lightresponsive metal-organic framework hybrid membranes can be obtained by in situ encapsulation of photoactive molecules (sulfonated spiropyran, SSP), as the molecular valve, into the cavities of the host ZIF-8. The configuration of SSP can be changed and switched reversibly in response to light, generating different mobile acidic protons and thus high on/off photoswitchable proton conductivity in the hybrid membranes and device. This device exhibits a high proton conductivity, fast response time, and extremely large on/off ratio upon visiblelight irradiation. This approach might provide a platform for creating emerging smart protonic solids with potential applications in the remote-controllable chemical sensors or protonconducting field-effect transistors.Many biological structures in nature can manipulate the substance transportation and signal transduction with the unique responsiveness to external stimuli, especially light. [1] An intriguing example is provided by bacteriorhodopsin (bR), a membrane protein known as light-activated proton pumps, which harvests energy from the light and generates proton gradients across the membrane to drive ATP production. [2] In contrast to biological materials, the artificial ones with better stability and modularity can be applied as biomimetics of light-driven proton pump and work under tough conditions. [3] Meanwhile, these abiotic materials can be utilized for the potential applications of fuel cells, chemical sensors, and electronic devices. Thus, developing protonic solids with light-responsivity has elicited unprecedented interest in the field of electronics and biology. [4] Nevertheless, the choice of appropriate materials is of great importance in order to endow artificial structure proton channels with more similar qualities to their biological counterparts.Metal-organic frameworks (MOFs) are a class of crystalline, porous materials with the structural feature of large specific surface areas, diverse skeleton composition, and tailorable pore chemistry and pore channels. [5] These appealing merits make MOFs hold great promise not only as the matrix for the multifunctional composites, but also as the platform for transporting channel of molecules and protons. [6] The applications of MOFs for proton conduction have been widely studied recently, and high proton conductivities (that is, 10 À4 -10 À1 S cm À1 ) have been achieved. [7] Current researches on proton-conducting MOFs have been mainly focused on the enhancement of proton conductivities for the potential fuel cell applications while light-responsive protonic conductive crystalline materials has been rarely explored.Very recently, a melting coordination polymer (CP) crystal ([Zn(HPO 4 )(H 2 PO 4 ) 2 ](ImH 2 ) 2 , ImH 2 = monoprotonated imidazole), as the grain-boundary-free processable materia...

Structural, dynamical, and photochemical properties ofortho-tetrafluoroazobenzene inside a flexible MOF under visible light irradiation

“…gas adsorption, 18,19 separation of gases 20,21 and liquids, [21][22][23] drug encapsulation and delivery, 24,25 incorporation of uorescent dyes, 26,27 photoconductivity, 28 or implementation in electronic devices, 29,30 this substance class has gained increasing attention in photoactive guest encapsulation. [31][32][33][34][35] Particularly, it was focused on the incorporation of the photochromic moiety as non-covalently attached guest molecules with stilbenes, 16 2-(phenylazo)pyridine (denoted as PAP in the following), 36,37 azobenzenes and (uorinated) derivatives (denoted as (xF-)AZB), [38][39][40][41][42][43] diarylethenes, 44 spiropyrans, [45][46][47][48] or spirooxazines. 49 Several functional materials with promising properties were obtained, e.g.…”

Tracking the light-induced isomerization processes and the photostability of spiropyrans embedded in the pores of crystalline nanoporous MOFs via IR spectroscopy

“…Re-conversion to the ground state is either achieved by visible light exposure or by heat treatment, which makes spiropyrans T-type chromophores. [2] N To enable photoswitching in the solid state, metal-organic frameworks (MOFs) [7] have recently been applied as porous host materials not only for spiropyrans [8][9][10][11] but for various photochromic molecules. [12][13][14][15][16][17][18] MOFs are composed of inorganic nodes and organic linker molecules that form 3 D frameworks with potential voids.…”

“…With respect to the embedment of photochromic molecules as non-covalently attached guest molecules, many functional materials with promising properties were obtained. Here, stilbenes [41] , 2-(phenylazo)pyridine [42,43] , azobenzenes and (fluorinated) derivatives [44][45][46][47][48][49] , diarylethenes [50] , spiropyrans [8][9][10][11] and spirooxazines [51] were applied and extrinsically introduced into different MOF host scaffolds.…”

Construction of Metal‐Organic Frameworks (MOFs)–Based Membranes and Their Ion Transport Applications

“…Most recently, Liang et al developed light‐switchable proton‐conductive MOF hybrid membranes, which were fabricated by the in situ encapsulation of photoactive molecular valves (sulfonated spiropyran (SSP)) into the cavities of ZIF‐8 (Figure 6b). [ 80 ] The configuration of SSP can be changed and switched reversibly in response to light, generating different mobile acidic protons. Notably, the SSP@ZIF‐8 membrane exhibited fast response time and outstanding gating properties with an ultrahigh on/off ratio of 2.8 × 10 4 upon visible light irradiation.…”