Controlling azobenzene photoswitching through combined <i>ortho</i>-fluorination and -amination

Ahmed, Zafar; Siiskonen, Antti; Virkki, Matti; Priimägi, Arri

doi:10.1039/c7cc07308a

Cited by 62 publications

(80 citation statements)

References 34 publications

(6 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This might be because the cis state of o-Fbs is more stable as reported previously and thus needs more time for back-isomerization. [23,57] Data for LCEs containing the o-Fb crosslinker 5 are shown in Table 2.…”

Section: Investigation Of Thermal and Photochemical Actuation Propertmentioning

confidence: 99%

“…[51] This is why much effort has been made to separate these n → π* bands, but also to boost visible light absorption and control cis lifetimes, through substitutions in the ortho-and para-positions of azobenzene structures. [51,[56][57][58][59] The Hecht group developed and investigated ortho-fluoroazobenzenes (o-Fbs). [51,56] The fluorine atoms in ortho-positions lower the energy of the n-orbital of the Z-isomer by reducing the electron density near the NN bond and as a result, cause a separation of the n → π* absorption band in the visible range of spectrum.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

Ditter

Braun

Zentel

2019

Macro Chemistry & Physics

View full text Add to dashboard Cite

In general, LCEs have gained great interest as stimuli-responsive and actuator materials in the last decades. [7-16] They consist of shape anisotropic molecules (mesogens) that are incorporated in a weakly crosslinked polymeric network (an elastomer). Therefore, they show the entropy elasticity of elastomers as well as the anisotropic characteristics of liquid crystals. Mesogens are either incorporated into the polymer backbone (main-chain LCE) or linked to it via flexible spacers (side-chain LCE). [17-20] They cause the molecular selforganization in liquid crystalline (LC) phases (mesophases). In nematic phases, for example, rod shaped mesogens align with their long axis roughly parallel to a common director and thus have directional but no positional order. [21,22] Integrated in a polymeric network, they act as an anisotropic environment for the polymer chains and stretch them to some extent in the mesophase. [7,13-16,23] On the other hand, in the isotropic state the order is lost and polymers can adopt their favored isotropic coil conformation. Switching between these states results in a macroscopic shape change if the LC state is present as a monodomain within the LCE sample. Shrinkage parallel to the director and expansion in the perpendicular direction are observed while the volume is kept constant. [13-16,24] These actuation properties had already been predicted by de Gennes in 1975. [25,26] So far, actuations up to 400% [27] could be observed for main-chain LCEs while side-chain LCEs could achieve actuations of up to 70% [26,28] corresponding to the increase in length. [7] To obtain a monodomain, LCE samples need to be pretreated to align mesogens before crosslinking. This is usually done in magnetic [29,30] or electric fields, [31] with the help of photoalignment layers [32,33] or by mechanical stretching of prepolymerized samples. [7,10] After alignment, crosslinking can occur via covalent or physical netpoints. [7,8,34] To investigate actuation properties of LCEs, it is necessary to switch between the liquid crystalline and the isotropic state. This requires an external stimulus. Such stimulus can be, for example, a change of temperature, [35] irradiation with light, [36,37] a pH change, [38] or the use of electric or magnetic fields. [39,40] Most attention has been paid to temperature changes. This often requires temperatures far beyond ambient temperature and mostly the whole actuator device has to be heated which results in high energy consumption. In contrast, light as a Actuation Systems In this article, the influences of ortho-fluoroazobenzenes (o-Fbs) on liquid crystalline (LC) phase stability and actuation properties of liquid crystalline elastomers (LCEs) are presented. Such o-Fbs find interest because they allow full photoswitching with visible light (no ultraviolet (UV) radiation). Novel o-Fb monomers and crosslinkers are synthesized and characterized. Different amounts of an LC mixture are replaced with synthesized o-Fbs successively and their influences on the LC phase stability in the cis...

show abstract

Section: Investigation Of Thermal and Photochemical Actuation Propertmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

Ditter

Braun

Zentel

2019

Macro Chemistry & Physics

View full text Add to dashboard Cite

show abstract

“…[b] Determined at 25 μ m in 50 m m Tris‐HCl pH 7.4 buffer + 1 % [D 6 ]DMSO. [c] Thermal relaxation half‐life times, as determined by the method of Ahmed et al . in 50 m m Tris‐HCl pH 7.4 buffer + 1 % [D 6 ]DMSO, extrapolating to 20 °C.…”

Section: Figurementioning

confidence: 99%

A Photoswitchable Agonist for the Histamine H₃ Receptor, a Prototypic Family A G‐Protein‐Coupled Receptor

et al. 2019

View full text Add to dashboard Cite

Spatiotemporal control over biochemical signaling processes involving G protein‐coupled receptors (GPCRs) is highly desired for dissecting their complex intracellular signaling. We developed sixteen photoswitchable ligands for the human histamine H3 receptor (hH3R). Upon illumination, key compound 65 decreases its affinity for the hH3R by 8.5‐fold and its potency in hH3R‐mediated Gi protein activation by over 20‐fold, with the trans and cis isomer both acting as full agonist. In real‐time two‐electrode voltage clamp experiments in Xenopus oocytes, 65 shows rapid light‐induced modulation of hH3R activity. Ligand 65 shows good binding selectivity amongst the histamine receptor subfamily and has good photolytic stability. In all, 65 (VUF15000) is the first photoswitchable GPCR agonist confirmed to be modulated through its affinity and potency upon photoswitching while maintaining its intrinsic activity, rendering it a new chemical biology tool for spatiotemporal control of GPCR activation.

show abstract

“…“Orange” amino‐substituted azobenzenes have an intermediate cis lifetime of minutes and slight redshift in the trans absorption band into the near‐UV or deep blue, while “red” pseudostilbenes have a very fast thermal reconversion to trans (seconds or milliseconds) and a far redshifted absorption well into the blue‐green or even low‐energy yellow visible spectral regions, and are thus by far the most attractive candidates for photoreversible biomaterials . This high variability in photochemical properties gives azobenzene a versatility advantage over other chromophores, as chemical substitution via a variety of possible synthetic routes affords a great deal of control over the resultant photophysical properties, and allows one to tune the absorption wavelengths away from high energy damaging UV, to far deeper into the low‐energy and more biologically benign visible region, yet still with 2 day cis half‐lives or longer (Figure b–d) . As long as the irradiation is kept to wavelengths in the visible or near‐UV, and limited to “sunlight‐like” intensities of 100 mW cm −2 or less, in general azo molecules are stable to photobleaching or other light degradation over time.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photoreversible Soft Azo Dye Materials: Toward Optical Control of Bio‐Interfaces

Chang

Fedele

Priimägi

et al. 2019

Advanced Optical Materials

View full text Add to dashboard Cite

systems interact with artificial materials, researchers have now assembled a versatile toolkit of materials and processes that allows one to fine-tune interactions at the interface, tailoring specific biological responses on demand. These strategies for biocontrol can be broadly categorized as chemical (charge, ligand presence, surface groups), material changes (moisture content, stiffness), or morphological changes (molecular orientation, surface topography, or mechanical actuation). Rational design of materials for biological interface applications has a unique set of challenges due to the unique requirements of a wide range of biological systems, since different tissues present specific compositions, with their own elasticity, structural organization, and triggering mechanisms. Even within a single organ or tissue, mechanical properties can vary widely depending on the region. A recent study of viscoelasticity in live mouse brain tissue for example found a tenfold difference within the brain depending on the region and morphological structure studied. [2] However, most biological tissues are far less stiff, and far more viscoelastic than typical artificial materials employed at their interface, especially early artificial cell culture materials, which can be much stiffer than in vivo extracellular matrix by many orders of magnitude. [3] In vivo, cells interface with a surrounding microenvironment consisting of an intricate macromolecular network of proteins and sugars swollen in an aqueous media gel. Therefore, the interaction between cells and the extracellular matrix (ECM) in the body is complex and involves a variety of cues related to topography, chemical markers, protein composition, solubility factors, and mechanical properties such as stiffness and elasticity (Figure 1a). [4] Yet much research over the past decades was focused on studying in vitro the effects of each of these signals on cell behavior, with a particular interest on the chemical factors, whereas only recently more advanced biomaterials with controlled physicomechanical properties have been developed, such as those with tunable and variable stiffness, alignment and orientation of key functional groups, and mechanical actuation. There is a large range of stiffness in human tissue, where bone (≈100 GPa) is nine orders of magnitude harder than brain tissue (≈0.1 kPa). [4] Therefore, biomaterial researchers assume a complex task of providing materials and processing technologies for controlling stiffness and micro-and nanostructures in Photoreversible optically switchable azo dye molecules in polymer-based materials can be harnessed to control a wide range of physical, chemical, and mechanical material properties in response to light, that can be exploited for optical control over the bio-interface. As a stimulus for reversibly influencing adjacent biological cells or tissue, light is an ideal triggering mechanism, since it can be highly localized (in time and space) for precise and dynamic control over a biosystem, and low-power visible light...

show abstract

Controlling azobenzene photoswitching through combined ortho-fluorination and -amination

Cited by 62 publications

References 34 publications

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

A Photoswitchable Agonist for the Histamine H₃ Receptor, a Prototypic Family A G‐Protein‐Coupled Receptor

Photoreversible Soft Azo Dye Materials: Toward Optical Control of Bio‐Interfaces

Contact Info

Product

Resources

About

Controlling azobenzene photoswitching through combined ortho-fluorination and -amination

Cited by 62 publications

References 34 publications

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

A Photoswitchable Agonist for the Histamine H3 Receptor, a Prototypic Family A G‐Protein‐Coupled Receptor

Photoreversible Soft Azo Dye Materials: Toward Optical Control of Bio‐Interfaces

Contact Info

Product

Resources

About

A Photoswitchable Agonist for the Histamine H₃ Receptor, a Prototypic Family A G‐Protein‐Coupled Receptor