Photoswitching Properties Research Articles

Synthesis and Self-Assembling Properties of Carbohydrate- and Diarylethene-Based Photoswitchable Molecular Gelators.

Carbohydrate-based low-molecular-weight gelators are interesting new materials with many potential applications. These compounds can be designed to include multiple stimuli-responsive functional groups. In this study, we designed and synthesized several chemically responsive bola-glycolipids and dimeric carbohydrate- and diarylethene-based photoswitchable derivatives. The dimeric glycolipids formed stable gels in a variety of solvent systems. The best performing gelators in this series contained decanedioic and dithienylethene (DTE) spacers, which formed gels in eight and nine of the tested solvents, respectively. The two new DTE-containing esters possessed interesting photoswitching properties and DTE derivative 7 was found to have versatile gelation properties in many solvents, including DMSO solutions at low concentrations. The gels formed by these compounds were stable under acidic conditions and tended to hydrolyze under basic conditions. Several gels were used to absorb rhodamine B and Toluidine blue from aqueous solutions. In this study, we demonstrated the rational design of molecular gelators which incorporated photoresponsive and pH responsive functions, leading to the discovery of multiple effective stimuli-responsive gelators.

Photo-switching and conductive properties of polymeric deep eutectic solvent-based tungsten oxide–zinc oxide nanocomposites

Photo-switching and conductive properties of polymeric deep eutectic solvent-based tungsten oxide–zinc oxide nanocomposites

A series of novel 1H-indole-7-carbohydrazide derivatives with photoswitching and AIE properties: “On-off” fluorescence sensors for Cu2+

In order to exploit novel fluorescent sensors with photoswitching properties, six fluorescent molecules were synthesized via coupling 1H-indole-7-carbohydrazide and corresponding substituted formaldehyde through an acylhydrazone bond. All title compounds were characterized via1H, 13C NMR, and elemental analysis, the single crystal structure of compound IC-PD was obtained via X-ray diffraction. The compounds IC-EL and IC-4PZ exhibited aggregation-induced emission (AIE) characteristics and also with regular responses to temperature and alkalinity in the solvent system dominated via deionized water. Probes IC-PL, IC-4PZ, and IC-PD could be used as fluorescence probes to detect copper (Ⅱ) with the LODs of 0.37, 0.27, and 0.26 μM in concentration of 0–50 μM, especially extraordinary bits of complex IC-PD-Cu2+ could also exhibited bright yellow in tetrahydrofuran (THF), which ensured the convenience of detection for Cu2+ ion. The exploration on the combination mechanism of representative compound IC-PD and Cu2+ ion via FT-IR and 1H NMR, which confirmed that the proton of hydrazide was protonated via Cu2+ ion, resulting in the excited state intramolecular proton transfer (ESIPT) process was interfered. When IC-PD was irradiation to the 302 nm photostationary state (PSS), the fluorescence emission intensity of IC-PD in THF was slightly enhanced, accompanied with the increased sensitivity of detection for Cu2+. Although the improvement was not significant, it was also provided a design foundation for the development of stimuli responsive fluorescent materials with photoswitching properties.

3-Pyridylazoindole derivatives as photoswitches: Synthesis, photoswitching behavior research, and applied to “on–off” fluorescence sensor for Cu2+ combined with theoretical calculations

In order to exploit the compounds with excellent photoswitching properties, a series of 3-pyridylazoindole derivatives were designed and synthesized. The molecular structures were characterized via1H and 13C NMR, the structure of typical compound A6 was also confirmed via single crystal X-ray diffraction. This series of 3-pyridylazoindole derivatives had outstanding characteristics compared with traditional azo photoswitches, such as the red-shifted of maximum absorption wavelength, UV/vis light isomerization in both directions (PSScis: 45–78%; PSStrans: 47–98%) can be achieved easily and broad range of trans-isomer thermal half-lives from minutes to days (0.44–38.4 h). The relationship between structure and properties verified that the photoswiching behavior of azo photoswitches was closely related to the conjugation groups and electronic effects modifying groups. Besides, the frontier molecular orbital and differences of spatial structure calculated by density functional theory (DFT) further explained the performance characteristics of photoswitches. What more, the compound A7 exhibited excellent aggregation-induced emission (AIE) property and could also be used as selective “on–off” fluorescence sensor for Cu2+, which expanded the photochemical properties of 3-pyridylazoindole derivatives.

Circularly polarized luminescence switch based on a photochromic europium(III) helicate derived coordination polymer

Chiroptical switches based on circularly polarized luminescence (CPL) have shown the promising applications in advanced information technologies. Herein, a pair of lanthanide coordination polymer enantiomers [Eu2(LR)3(BTFPO)2]n and [Eu2(LS)3(BTFPO)2]n with light-regulated CPL property are designed, which are assembled by a chiral binuclear triple-stranded Eu3+ helicates [Eu2(LR/S)3] coordinated with two photochromic triphenylphosphine oxides (BTFPO). Upon the alternative UV and 526 nm light irradiation, the complexes show the reversible photochromism, PL and CPL responses. Notably, the luminescence dissymmetry factor, glum of 5D0→7F1 (591 nm) transition shows an obvious increase from 0.19 to 0.29 before and after 275 nm light irradiation. Additionally, the emission from Eu3+ center is not completely quenched in closed-ring state due to the low photocyclization (Фo-c) quantum yield of the polymer. The partial maintenance of emissive intensity is of essential importance for the monitor of CPL signal. More importantly, the CPL photo-switching property of the complexes in solid hybrid film is maintained, and still displays the enhanced CPL emission in photostationary state. Further, the potential applications of the doping film in logic gate and anti-counterfeiting were investigated.

Easily Accessible Substituted Heterocyclic Hemithioindigos as Bistable Molecular Photoswitches.

Thioaurone chromophores, part of the indigoid family and commonly named hemithioindigos, have recently gained attention due to their interesting photoswitching properties. The study focuses on heterocyclic hemithioindigos (Het-HTIs) and investigates their synthesis using electron-rich and electron-poor heterocycles and modifications to the thioindigo moiety. Furthermore, it aims to evaluate the photoswitching performances of these synthesised compounds, with a particular emphasis on the influence of the heterocycles on the photoisomerization capabilities, which was found to be more prominent than the modifications made to the thioindigo moiety. Among the 44 Het-HTIs tested, several exhibited highly efficient photoswitchable properties, demonstrating Z-to-E photoisomerization in the blue region, and E-to-Z photoisomerization in the green or the red regions. Additionally, the metastable E-isomer displayed an impressive half-life of up to 54 days in a polar solvent (DMSO). These results suggest that heterocyclic hemithioindigos hold great promise as photoswitches for researchers interested in light-controlled molecular mechanisms.

The photodetection properties of a ruthenium electro-optic device for organic material-based device industry

The electrical properties and effect of illumination on the photodetection properties were investigated for the fabricated device with Ru(II)-pydim complex interface layer. The Ru(II)-pydim interface was deposited by spin coating technique on a p-silicon substrate. The electrical and optoelectrical parameters of photodiode were analyzed via the current-voltage (I–V), capacitance/conductance-voltage (C/G-V) measurements under dark and different illumination power. The fabricated device has good electrical parameters such as the rectification ratio of 2.726 × 104, the ideality factor of 1.328, and barrier height of 0.805 eV under the dark condition. The current values of the device with Ru(II)-pydim interface at reverse bias were strongly dependent on the illumination intensities, confirming its photoconduction behavior. The I–V measurements under different solar illuminations present that the electro-optic device with Ru(II)-pydim complex as an interface has good photodiode parameters with the responsivity of 131 mA/W, and the detectivity of 1.63 × 1011 Jones at 100 mW/cm2. The photo transient measurements demonstrate that the Ru(II)-pydim complex based photodiode presents the desired photo-switching property. Therefore, the prepared Ru(II)-pydim based device can be used for electro-optic and photonic applications, particularly in the rapidly developing organic material-based device industry.

Novel salicylic acid derivatives connecting to five-membered cycle through an acyl hydrazone bond as multi-stimuli responsive fluorescent smart materials with photoswitching properties

In order to exploit novel multi-stimuli responsive fluorescent materials, a series of novel fluorescent molecules of salicylic acid derivatives were designed and synthesized via introducing pyrazole or cyclopentane to the salicylic acid scaffold through a special Schiff base–acylhydrazone, and the molecular structures of representative compounds A2 and A4 were verified via single crystal X–ray diffraction. All title molecules could exhibit obvious solvatofluorochromism from cyan to indigo in several solutions with different polarity. The fluorescence titration data exhibited compound A2 and complex A2-Cu2+ with prime detection limits to Cu2+ (0.24 μM) and S2- ions (2.83 μM). The sensitive recognition of A2 to trifluoroacetic (TFA) and A2-TFA to triethylamine (TEA) were also confirmed via fluorescent titration experiments in various solutions, respectively. What’s more, the 1H NMR and UV/Vis absorption spectra further explained the mechanism between molecules and ions or molecules and TFA/TEA. Besides, the photoswitching properties of the compounds A2 and A3 could be demonstrated via the irradiation of special wavelength light or heating accompanied with changes in quantum yields. In addition, these phenomena of multiple responses were explained via Density Functional Theory (DFT) based on the Gaussian calculations. Thus, this work provided a preliminary basis for the research of multi-stimuli responsive fluorescent molecules with photoswitching properties.

Reversible Light-Induced Dimerization of Secondary Face Azobenzene-Functionalized β-Cyclodextrin Derivatives.

β-cyclodextrin (βCyD) derivatives equipped with aromatic appendages at the secondary face exhibit tailorable self-assembling capabilities. The aromatic modules can participate in inclusion phenomena and/or aromatic-aromatic interactions. Supramolecular species can thus form that, at their turn, can engage in further co-assembling with third components in a highly regulated manner; the design of nonviral gene delivery systems is an illustrative example. Endowing such systems with stimuli responsiveness while keeping diastereomeric purity and a low synthetic effort is a highly wanted advancement. Here, we show that an azobenzene moiety can be "clicked" to a single secondary O-2 position of βCyD affording 1,2,3-triazole-linked βCyD-azobenzene derivatives that undergo reversible light-controlled self-organization into dimers where the monomer components face their secondary rims. Their photoswitching and supramolecular properties have been thoroughly characterized by UV-vis absorption, induced circular dichroism, nuclear magnetic resonance, and computational techniques. As model processes, the formation of inclusion complexes between a water-soluble triazolylazobenzene derivative and βCyD as well as the assembly of native βCyD/βCyD-azobenzene derivative heterodimers have been investigated in parallel. The stability of the host-guest supramolecules has been challenged against the competitor guest adamantylamine and the decrease of the medium polarity using methanol-water mixtures. The collective data support that the E-configured βCyD-azobenzene derivatives, in aqueous solution, form dimers stabilized by the interplay of aromatic-aromatic and aromatic-βCyD cavity interactions after partial reciprocal inclusion. Photoswitching to the Z-isomer disrupts the dimers into monomeric species, offering opportunity for the spatiotemporal control of the organizational status by light.

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli

Impact of terminal group on azobenzene liquid crystal dimers for photo-responsive optical storage devices

Three new series of photo responsive dimers bearing different terminal functional groups (-CN, -COOEt, -OMe) and variable aliphatic spacers have been synthesized and investigated in detail. The molecular structures of the new materials were proved using different spectroscopic techniques and their liquid crystal self-assembly was characterized using differential scanning calorimetry (DSC), polarized light microscope (POM) and X-ray diffraction (XRD). Moreover, their photo switching behaviour was investigated in details in solution. The results revealed that, almost all members of the dimeric materials are mesomorphic exhibit either nematic or both smectic A and nematic phases. Under UV illumination the materials show interesting photo-switching properties, reaching a photo-stationary state in 40 s and a thermal back-relaxation time of approximately 35 h in solution. Finally, a fabricated device authenticates the potential of the reported materials for optical storage devices.

Simultaneous S-scheme promoted Ag@AgVO3/g-C3N4/CeVO4 heterojunction with enhanced charge separation and photo redox ability towards solar photocatalysis

Photocatalytic removal of toxic contaminants is one of the emerging techniques for water remediation, but it suffers from low redox ability, charge recombination and poor light harvesting efficiency. The present work reports a simultaneous S-scheme promoted by CeVO4/g-C3N4/Ag@AgVO3. The formation of the S-scheme mechanism enhanced the generation of photogenerated carriers and also improved the redox ability of the electrons and holes in the reduction and oxidation photocatalysts. The ternary demonstrated remarkable photo switching properties along with efficient charge separation which was achieved through dual interfacial interaction within the ternary (Ag@AgVO3/g-C3N4 and CeVO4/g-C3N4). The heterojunction formation was verified through the shift in binding energy spectra in the X-ray Photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy analysis (HR-TEM). The ternary demonstrated reduced PL intensity, width of space charge region and an upsurge in photogenerated current density in the order of 93 μA/cm2 (∼6X higher than all the pristine). This resulted in efficient removal of methyl orange, methylene blue and endocrine disruptive bisphenol-A with a removal rate of 0.02 min−1, 0.03 min−1 and 0.0087 min−1 and an apparent quantum yield of 4.6 × 10−9 (Methylene Orange), 6.89 × 10−9 (Methylene Blue) and 2 × 10−9 (Bisphenol A/H2O2).

Photo‐responsive Single‐Molecule Magnet Showing 0D to 1D Single‐Crystal‐to‐Single‐Crystal Structural Transition and Hysteresis Modulation

AbstractPhoto‐responsive lanthanide‐based single‐molecule magnets (SMM) hold great promise for future switching and memory devices. Herein, we report a dysprosium phosphonate [DyIII(SCN)2(NO3)(depma)2(4‐hpy)2] (1Dy), which features a supramolecular framework containing layers of hydrogen‐bonding network and pillars of π–π interacted anthracene units. The photocycloaddition reaction of anthracene pairs led to a rapid and reversible single‐crystal‐to‐single‐crystal (SC–SC) structural transition to form the 1D coordination polymer [DyIII(SCN)2(NO3)(depma2)(4‐hpy)2]n (2Dy), accompanied by photoswitchable SMM properties with the reduction of effective energy barrier by half and the narrowing of the butterfly‐like hysteresis loop. The diluted sample showed a photo‐induced switch of the blocking temperature (TB) from 3.8 K for 1Dy@Y to 2.6 K for 2Dy@Y. This work may inspire the construction of lanthanide‐based molecular materials with targeted photo‐responsive magnetic properties.

Photo-responsive Single-Molecule Magnet Showing 0D to 1D Single-Crystal-to-Single-Crystal Structural Transition and Hysteresis Modulation.

Photo-responsive lanthanide-based single-molecule magnets (SMM) hold great promise for future switching and memory devices. Herein, we report a dysprosium phosphonate [DyIII (SCN)2 (NO3 )(depma)2 (4-hpy)2 ] (1Dy), which features a supramolecular framework containing layers of hydrogen-bonding network and pillars of π-π interacted anthracene units. The photocycloaddition reaction of anthracene pairs led to a rapid and reversible single-crystal-to-single-crystal (SC-SC) structural transition to form the 1D coordination polymer [DyIII (SCN)2 (NO3 )(depma2 )(4-hpy)2 ]n (2Dy), accompanied by photoswitchable SMM properties with the reduction of effective energy barrier by half and the narrowing of the butterfly-like hysteresis loop. The diluted sample showed a photo-induced switch of the blocking temperature (TB ) from 3.8 K for 1Dy@Y to 2.6 K for 2Dy@Y. This work may inspire the construction of lanthanide-based molecular materials with targeted photo-responsive magnetic properties.

Deep-tissue photoacoustic imaging of photoswitchable transgenic mouse models

Compared with visible light, near-infrared (NIR) light (700–1300 nm) is capable of deep-tissue penetration because of low tissue attenuation, and thus holds great promise for deep-tissue optical manipulation and imaging. In this work, we take advantages of the NIR Rhodopseudomonas palustris bacterial phytochrome photoreceptors (BphP1) and generate a loxP-BphP1 photoswitchable transgenic mouse model that enables Cre-dependent temporal and spatial targeting of BphP1 expression at the whole-body scale in vivo. This BphP1 phytochrome incorporates biliverdin chromophore and reversibly switches between the ground state and activated state, which enabled the light-controlled manipulation of gene expression and differential detection in photoacoustic tomography (PAT). We first validated the optogenetic performance of BphP1 that binds its engineered protein partner QPAS1 to trigger gene transcription in primary cells and living mice, and demonstrated its superior capability of deep-tissue optogenetics over the existing visible-light proteins. Then, by taking advantage of PAT's deep-tissue non-invasive imaging ability and the BphP1's photoswitching properties, we can suppress the non-switching signals from background blood and improve the molecular detection sensitivity by three orders of magnitude. This study shows the BphP1-encoded photoswitchable transgenic mouse model can be used for both NIR optogenetic manipulation and deep-tissue PAT.

Photoswitchable Nanoporous Metal–Organic Framework Monolayer Film for Light-Gated Ion Nanochannel

Two-dimensional metal–organic framework (MOF) monolayer films, which can be considered as large-area, periodically ordered thin films with atom- or single-unit thickness, have attracted extensive attention due to their special properties and wide range of potential applications. However, the preparation of MOF monolayer films is still a great challenge, and the introduction of functional groups into MOF monolayer films is seldom reported. Here, we report the first centimeter-scale, photo-switchable, free-standing MOF monolayer film formed by self-assembly of poly(methyl methacrylate-co-acrylamidoazobenzene)-coated MOF nanoparticles at the water–air interface. This self-assembled MOF monolayer film is extremely thin (∼220 or 50 nm) and has a high MOF loading (85 wt %), while exhibiting remarkable reversible photoswitching properties under alternating exposure to 365 nm UV and white light. Inspired by this, a light-gated ion nanochannel device is fabricated, which enables reversible ″OFF–ON″ changes of the ionic flux and has promising applications in the field of photoelectric conversion. This provides a modular route to design large-area, free-standing functional MOF monolayer films.

Thiacalixarene Appended Azo-based Supramolecular Systems: Self-assembly and Photo Tuning Reversible Liquid Crystalline Properties.

Four new azo-based supramolecular materials containing thiacalixarene core substituted by variable alkoxy groups (TFA1 -TFA4 ) have been designed and synthesized for the mesomorphic and photoswitching properties. The liquid crystalline behavior were accomplished by using DSC, POM, and XRD studies. All azo-based thiacalixarene based materials with short and higher chain length display columnar hexagonal mesophase with broad temperature range. The thermal behavior of all the materials was investigated by DSC and TGA study. The structural and conformational study of the lower rim functionalized materials was confirmed by using different techniques. These thiacalixarene moulded liquid crystalline compounds shows columnar self-assembly type behavior and higher thermal stability. The introduction of bi-substituted azo-ester network towards the lower rim of thiacalixarene core has impact on the electron delocalization and liquid crystalline properties. The photoswitching properties suggested cis and trans azo-isomerization under radiation of UV light and higher thermal back relaxation time. The mesogenic behaviour of compound TFA2 and TFA4 were demolished by the influence of cis and trans isomerization. The structure-property correlation is studied to understand the variation in mesogenic properties with the substitution of variable alkoxy side chain.

Expanded furan-containing helicene π-systems: Synthesis, crystal analyses, physical and photoswitching properties

Two novel expanded furan-containing helicene derivatives 6a and 12a have been conveniently synthesized and fully characterized. Compared with the precursors 5 and 11, the cyclized molecules 6a and 12a exhibit red-shifted absorption and emission. The former 6a can form radical cations in the presence one-electron oxidant AgSbF6 but the latter 12a cannot be oxidized. Besides, compounds 6a, 12a and their precursors 5, 11 presents promising photoswitching responses.

Polythiophene-g-poly(methacrylic acid) and perylene diimide appended peptide conjugates with tuneable photoluminescence, OMEIC, and photo-switching properties

Polythiophene-g-poly(methacrylic acid) conjugates with protonated perylene diimide appended dipeptide show both AIE and AIQ in fluorescence, enhancement of dc-conductivity, generate OMEIC property, and exhibit tuneable photo-switching behaviour.

Design rules for optimization of photophysical and kinetic properties of azoarene photoswitches.

Azoarenes are an important class of molecular photoswitches that often undergo E → Z isomerization with ultraviolet light and have short Z-isomer lifetimes. Azobenzene has been a widely studied photoswitch for decades but can be poorly suited for photopharmacological applications due to its UV-light absorption and short-lived Z-isomer half-life (t1/2). Recently, diazo photoswitches with one or more thiophene rings in place of a phenyl ring have emerged as promising candidates, as they exhibit a stable photostationary state (98% E → Z conversion) and E-isomer absorption (λmax) in the visible light range (405 nm). In this work, we performed density functional theory calculations [PBE0-D3BJ/6-31+G(d,p)] on 26 hemi-azothiophenes, substituted with one phenyl ring and one thiophene ring on the diazo bond. We calculated the E-isomer absorption (λmax) and Z-isomer t1/2 for a set of 26 hemi-azothiophenes. We compared their properties to thiophene-based photoswitches that have been studied previously. We separated the 26 proposed photoswitches into four quadrants based on their λmax and t1/2 relative to past generations of hemi-azothiophene photoswitches. We note 8 hemi-azothiophenes with redshifted λmax and longer t1/2 than previous systems. Our top candidate has λmax and a t1/2 approaching 360 nm and 279 years, respectively. The results here present a pathway towards leveraging and optimizing two properties of photoswitches previously thought to be inversely related.