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Esters of 4-nitrocinnamic acids and 4-halogene-4’-hydroxyazobenzenes – synthesis, mesogenic and optical studies
摘要： Six new compounds were synthesized that have no alkyl chains in their structure: 4-nitrocinnonates of 4-hydroxyazobenzene, 4-nitro-4'-hydroxyazobenzene, 4-fluoro-4'-hydroxyazobenzene, 4-chloro-4'-hydroxyazobenzene, 4-bromo-4'-hydroxyazobenzene, and 4-iodo-4'-hydroxyazobenzene. Using the polarizing microscopy and differential scanning calorimetry, enthalpies and temperatures of phase transitions were determined. All investigated compounds have an enantiotropic nematic phase. These compounds proved to be extremely thermally stable. Thermal decomposition was observed in temperatures above 300°C. Investigated compounds contain two different chromophore groups (i.e. azo and ethene moieties), which influenced the complex trans–cis isomerization processes of both groups (three time-separated processes were observed). It was shown that the presence of the ethene group significantly shifts the π-π* band towards higher energies. The substituent polarity in the azo group also affected the energy of this absorption band. A weak luminescence effect was observed in the 4-nitrocinnonates of 4-hydroxyazobenzene compound.
关键词： nematic,luminescence,Azobenzenes,trans–cis isomerization,polarizing microscopy,DSC calorimetry
更新于2025-09-23 15:23:52
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Photoresponsive Halogen-Bonded Liquid Crystals: The Role of Aromatic Fluorine Substitution
摘要： A new strategy for controlling the liquid crystalline and photophysical properties of supramolecular mesogens assembled via halogen bonding is reported. Changing the degree of fluorination at the halogen-bond donor of the supramolecular liquid crystal allows for the fine-tuning of the halogen bond strength and thereby provides control over the temperature range of the mesophase. At least three fluorine atoms have to be present to ensure efficient polarization of the halogen-bond donor and the formation of a mesophase. In addition, it was found that stilbazole acceptors are superior to their azopyridine counterparts in promoting stable liquid crystalline phases. The halogen-bond-driven supramolecular liquid crystals between fluorinated azobenzenes and stilbazole/azopyridine acceptors show a rich variety of photoinduced processes driven by azobenzene photoisomerization, dictated not only by the photochemical properties of the molecular components but also by the difference between the operation temperature and the clearing point.
关键词： photoresponsive materials,fluorination,supramolecular chemistry,azobenzenes,halogen bonding,liquid crystals
更新于2025-09-23 15:23:52
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Optically Responsive, Smart Anti-Bacterial Coatings via the Photofluidization of Azobenzenes
摘要： Antibacterial strategies sans antibiotic drugs have recently garnered much interest as a mechanism by which to inhibit biofilm formation and growth on surfaces due to the rise of antibiotic-resistant bacteria. Based on the photofluidization of azobenzenes, we demonstrate for the first time the ability achieve up to a 4 log reduction in bacterial biofilms by opto-mechanically activating the disruption and dispersion of biofilms. This unique strategy with which to enable biofilm removal offers a novel paradigm with which to combat antibiotic resistance.
关键词： photofluidization,azobenzenes,photoresponsive polymers,antibacterial and antifouling strategies,optically responsive materials,antibacterial coatings,smart materials
更新于2025-09-23 15:23:52
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Influence of 4-[(E)-(4′-Heptyloxyphenyl)diazenyl]phthalonitrile on the Properties of a Cyanobiphenyl Liquid Crystal Mixture
摘要： The mesomorphic properties of 4-[(E)-(4'-heptyloxyphenyl)diazenyl]phthalonitrile (7O-AB-CN2) were studied by polarization microscopy and DSC method. Liquid crystalline phase formation was observed over a broad temperature range of 92 to 181°C. The influence of 7O-AB-CN2 on the mesomorphic, dielectric, and optical properties of a liquid crystalline mixture of n-alkyloxycyanobiphenyls was examined. Enhancement of the dielectric anisotropy of the mesomorphic composition due to high polarity of 7O-AB-CN2 and its effective inclusion into the liquid crystalline matrix was revealed.
关键词： dielectric anisotropy,cyanobiphenyls,birefringence,liquid crystals,phthalonitrile,azobenzenes
更新于2025-09-23 15:21:21
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Allosteric Control of Photofoldamers for Selecting between Anion Regulation and Double-to-Single Helix Switching
摘要： Allosteric regulation of protein structure and function is a hallmark of biology. The structures of protein-like abiological foldamers have been subject to allosteric control, however, regulation of their function is rare. We report this behavior using a photoactive foldamer following the discovery that small and large anions select between single and double helical structures, respectively. Correspondingly, these anions activate different functions in the photofoldamer; small anions turn on photoregulation of anion concentrations while large anions turn on chiroptical switching of quaternary structure. For this demonstration, we used an aryl-triazole based photofoldamer in which the light-driven trans-cis isomerization of azobenzenes alters intrastrand π-π contacts while the triazoles define the allosteric anion-binding site. Binding to eleven anions of increasing size was quantified (Cl–, Br–, NO2–, I–, NO3–, SCN–, BF4–, ClO4–, ReO4–, PF6–, SbF6–). Contrary to expectations that single helices will expand to accommodate larger and larger guests, this behavior only occurs for smaller anions (Cl– – NO3–; < 45 ?3) beyond which the larger anions form double helices (SCN– – SbF6–; > 45 ?3). With small anions, the single helix regulates anion concentrations when the azobenzenes are photoswitched. The binding of large anions favors a chiral double helix and activates light-driven switching into racemic single helices thereby modulating the quaternary structure and chiroptical activity. This work shows how complex multifunctional outcomes emerge when allosteric changes in structure are expressed in intrinsically functional foldamers.
关键词： Aryl-triazole,Double-to-Single Helix Switching,Anion Regulation,Allosteric Control,Azobenzenes,Photofoldamers
更新于2025-09-11 14:15:04
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Thermophysical properties of methacrylic polymer films with guest-host and side-chain azobenzene
摘要： The methacrylic polymer films containing azobenzenes with different peripheral substituents in the form of side-chain (P) and guest-host (A) systems were thermally investigated. The azo polymers with thicknesses below 1 μm were deposited on glass substrates using spin coating method. Photothermal radiometry (PTR) and scanning thermal microscopy (SThM) were used for determination of thermophysical properties of polymer samples. The topography of studied compounds was examined by atomic force microscopy (AFM). The results showed the influence of peripheral substituents as well as that of the polymer system on the thermophysical properties of studied azo polymers. Thermal diffusivity (α) extracted from PTR measurements is between 5.56 10-8 m2s-1 and 11.3?10-8 m2s-1 for A samples, 2.76 10-8 m2s-1 and 7.62?10-8 m2s-1 for P samples depending on the substituent. Likewise, thermal effusivity (ε) changes from 474 Ws1/2m-2K-1 to 532 Ws1/2m-2K-1 for A, and from 473 Ws1/2m-2K-1 to 564 Ws1/2m-2K-1 for P samples. The volumetric heat capacity (Cv) and in-depth thermal conductivity (κ) were calculated on the base of PTR results. Local κ obtained from SThM measurements is between 0.15 Wm-1K-1 and 0.22 Wm-1K-1 due to different substituents and polymer system. Thermal studies performed in this work provide valuable information for engineers designing azobenzene polymer thin films based devices and supplement the knowledge of their thermal behavior in the system.
关键词： polymer,nanomaterials,thermophysical properties,thin films,azobenzenes
更新于2025-09-09 09:28:46
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Ultrafast Dynamics of Encapsulated Molecules Reveals New Insight on the Photoisomerization Mechanism for Azobenzenes
摘要： Spatial con?nement can have a profound impact on the dynamics of chemical reactions, especially for isomerization reactions that involve large amplitude structural rearrangement of a molecule. This work uses ultrafast spectroscopy to probe the e?ects of con?nement on trans→cis photoisomerization following ππ? excitation of 4-propyl stilbene and 4-propyl azobenzene encapsulated in a supramolecular host-guest complex. Transient absorption spectroscopy of the encapsulated azobenzene derivative reveals the formation of two distinct excited-state species with spectral signatures resembling the cis and trans isomers. Formation of the cis species indicates a direct excited-state isomerization channel that is not observed in cyclohexane solution. Comparison with the stilbene analogue suggests that this “hot” excited-state isomerization pathway for encapsulated azobenzene involves primarily in-plane inversion, whereas a ten-fold increase of the excited-state lifetime for the trans isomer suggests that crowding in the capsule hinders isomerization from the relaxed S1 geometry of the trans isomer. This work provides new mechanistic insight on the relative roles of inversion and rotation in the ultrafast photoisomerization of azobenzene derivatives.
关键词： Azobenzenes,Encapsulated molecules,Supramolecular host-guest complex,Photoisomerization,Ultrafast dynamics
更新于2025-09-04 15:30:14