Stilbene Units Research Articles

Modulation of room temperature emission characteristics of heteroleptic ruthenium-terpyridine complexes via aggregation

In this work, we have thoroughly investigated the modulation of room temperature luminescence characteristics of our recently reported stilbene-appended heteroleptic Ru(II)-terpyridine complexes of the type, [(tpy-PhCH3)Ru(tpy-pvp-X)](ClO4)2, wherein X =naphthalene, anthracene, and pyrene moiety via aggregation through the use of appropriate solvent mixtures. Taking profit of the polyaromatic motif, the complexes display both aggregation-induced emission quenching as well as emission augmentation, depending upon nature of the solvent mixtures. By virtue of the presence of stilbene unit, the complexes undergo trans–cis isomerization upon irradiation of light. We have previously investigated the reversible trans–cis isomerization of the non-aggregated form of the complexes upon alternative treatment of visible and UV light. In the present study, we have also undertaken the trans → cis photoisomerization of the aggregated forms of the complexes. The rate constant and quantum yield of photoisomerization in the aggregated form of the complexes are also estimated and compared with their non-aggregated counterparts.

Novel resveratrol-based hyperbranched epoxy resin suitable for comprehensive modification of epoxy resins

Hyperbranched epoxy resins are efficient modifiers for epoxy resins but still require simultaneous improvements in terms of thermomechanical/mechanical properties and thermal stability. Herein, a novel resveratrol-based hyperbranched polyether epoxy resin (HBPEER) was designed for all-purpose epoxy resin modification. To this end, hyperbranched polyether with terminal phenolic hydroxyl groups was first synthesized from commercially available 1,6-dibromohexane (A2-type monomer) and resveratrol (B'B2-type monomer). Surface modification with epichlorohydrin was afterward implemented to produce hyperbranched polyether with terminal epoxy groups (HBPEER). Next, various HBPEER-modified epoxy thermosets were prepared and characterized. The results suggested that compared to the neat diglycidyl ether of bisphenol A (DGEBA) thermoset, the 6 wt% HBPEER-modified epoxy thermoset showed an increase in impact strength, elongation at break, critical stress intensity factor (KIC), critical crack propagation energy release rate (GIC), flexural strength, tensile strength, storage modulus, glass transition temperature (Tg), and initial thermal decomposition temperature (Td5%) by 69.6 %, 87.0 %, 32.0 %, 68.2 %, 29.3 %, 37.0 %, 8.1 %, 3.5 %, and 1.6 % respectively. Moreover, the dielectric constant and loss of 6 wt% HBPEER-modified epoxy thermoset decreased by 16.2 % and 16.5 %, respectively. Such comprehensive performance modifications were caused by the combined effects of crosslink density improvement, efficient intramolecular cavity, rigid stilbene units, and flexible aliphatic backbone of HBPEER.

Three-step synthesis of flavanostilbenes with a 2-cyclohepten-1-one core by Cu-mediated [5 + 2] cycloaddition/decarboxylation cascade

The first synthesis of flavanostilbenes with a 2-cyclohepten-1-one core was carried out by applying an effective strategy in three steps from abundant polymerized flavanol resources. A key regio- and stereoselective Cu-mediated [5 + 2] cycloaddition/decarboxylation cascade was explored and applied without the use of protecting groups, and water as an environmentally friendly solvent contributed to the cascade. The intramolecular [5 + 2] cycloaddition mechanism, involving oxidation and dearomatization of the flavanol unit as a diene, was proposed and supported by the synthesis of the intermediate. The regioselectivity of the cyclization was found to be dependent on the substitution effects of the stilbene units by the exploration of substrate scope.

Ether Bond Cleavage of a Phenylcoumaran β-5 Lignin Model Compound and Polymeric Lignin Catalysed by a LigE-type Etherase from Agrobacterium sp.

A LigE-type beta-etherase enzyme from lignin-degrading Agrobacterium sp. has been identified, which assists degradation of polymeric lignins. Testing against lignin dimer model compounds revealed that it does not catalyse the previously reported reaction of Sphingobium SYK-6 LigE, but instead shows activity for a β-5 phenylcoumaran lignin dimer. The reaction products did not contain glutathione, indicating a catalytic role for reduced glutathione in this enzyme. Three reaction products were identified: the major product was a cis-stilbene arising from C-C fragmentation involving loss of formaldehyde; two minor products were an alkene arising from elimination of glutathione, and an oxidised ketone, proposed to arise from reaction of an intermediate with molecular oxygen. Testing of the recombinant enzyme against a soda lignin revealed the formation of new signals by two-dimensional NMR analysis, whose chemical shifts are consistent with the formation of a stilbene unit in polymeric lignin.

Stilbene-incorporated platinum(II) di-yne electrocatalysts for generating hydrogen from acetic acid

Molecular hydrogen (H2) is a potential alternative to fossil fuels since it is a green energy source with high energy density and non-polluting combustion materials. We present herein the electrochemical properties and hydrogen evolution reaction (HER) ability of two Pt(II) diynes (Pt-Sb-Pt & Sb-Pt-Sb) bearing stilbene unit. Both complexes catalyzed the HER in acidic media. In addition, density functional theory (DFT) calculation was carried out at B3LYP/LANL2DZ level of theory in gas phases as well as in the solvent (DMF) to delineate the possible mechanism of HER. We demonstrated that the studied Pt(II) electrocatalysts shift the reduction potential noticeably. However, no apparent role of photo-switchable stilbene fragment on electrolysis was observed and the presence of ethynyl moiety was necessary for stabilization of the metal center. To the best of our knowledge, this is the first study highlighting the electrocatalytic HER by platina-ynes.

Facile synthesis of stilbene-derivatized Schiff base ligands and their Cu(II) complexes

Herein we present the synthesis and characterization of three Schiff base ligands derivatized with stilbene groups and their Cu(II) complexes CuL1-3, prepared in only three synthetic steps, from simple aromatic rings to complexes. The ligands L1-3 were synthesized first by the CC coupling of an aryl bromide and styrene via a Heck reaction to produce a stilbene and then, by a condensation reaction between the stilbene and an aliphatic diamine to form tetradentate Schiff base ligands L1-3. CuL1-3 were then easily formed by complexation of Cu(II) ion in ethanolic media and obtained pure and in high yields. The complexes, ligands, and intermediates were fully characterized using FTIR, UV–vis, and NMR spectroscopy, as well as HRMS and XRD. These compounds exhibit two stilbene units, a functional group that has shown high affinity for amyloid plaques, an important biomarker of Alzheimer’s disease. Thus, these compounds have the potential to be studied as radioimaging agents for the diagnosis of Alzheimer's by positron emission tomography (PET) when prepared with the positron-emitting radioisotope Cu-64.

Shrinkable/stretchable bis(calix[4]arenes) comprising photoreactive azobenzene or stilbene linkers

The readily available azobenzene/stilbene-linked bis(calix[4]arenes) undergo longitudinal shrinking/stretching upon irradiation/heating due to E/Z isomerization of both linkers, or may undergo intramolecular [2 + 2]-photocycloaddition.

Rapid Methods of Synthesis of Stilbene and Phenylethynylstilbene Arms

Stilbene and phenylethynylstilbene units are excellent candidates for fluorescent sensor synthesis. In this paper we show a fast and efficient method for the preparation of fluorophores based on biphenyl nuclei with phenylene-vinylene units functionalized by donor groups. Using pallado catalysed coupling reactions of Sonogashira types and Wittig or Wittig-Horner reaction, the stilbene and phenylethylsilbene arms functionalized with O-alkyl and N-alkyl donor groups were synthesized.

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

Energy technical light output of scintillators – problems of assessment and an alternative method for their solution

The paper analyzes the problems that arise when assessing the energy technical light output by existing methods. A modern alternative method for assessing the energy technical light output of various scintillators produced by the Institute of Scintillation Materials of the National Academy of Sciences of Ukraine is described.
 The possibility of evaluating the technical light output of any scintillator by relative comparison with a reference stilbene-based scintillator with a known technical light output is shown. The resulting ratio of responses is recalculated in ph/MeV by taking into account the technical light output of the reference scintillator, equal to 0.023, and the photon formation energy of a particular scintillator.
 The estimation procedure is described. Expressions are given for calculating the values of the technical light yield of scintillators in stilbene units and in ph/MeV. The radioluminescence spectra of the tested scintillators are compared with the sensitivity spectra of the normalized and laboratory photodetectors.
 The technical light yield of scintillators based on single crystals of NaI(Tl), CsI(Tl), CWO, BGO, p-terphenyl, anthracene, stilbene, and a plastic scintillator has been estimated. The values of the responses amplitudes ratio, the spectral normalization coefficients and the tested scintillators technical light output were obtained in stilbene units and in ph/MeV. To check the adequacy of the method the calculation of the tested inorganic scintillators absolute light output was carried out using the light collection coefficients values given in the literature.
 It is shown that with an increase in the scintillators technical light output, in stilbene units, from 0.26 for BGO to 4.3 for NaI(Tl), their technical light output increases from 2500 ph/MeV to 33100 ph/MeV. A decrease in the scintillation photon energy from 2.988 (l = 415 nm) for NaI(Tl) to 2.214 (l = 560 nm) for CsI(Tl) also increases the technical light output of the latter to 35300 ph/MeV. The performed estimates accuracy of scintillators technical light output was 8%.

Light and Cation-Driven Optical Switch based on a Stilbene-Appended Terpyridine System for the Design of Molecular-Scale Logic Devices

A molecular system comprising a terpyridine moiety capable of coordinating with different cations and a photoswitchable stilbene unit has been utilized here for the fabrication of multiply configurable logic systems. Incorporation of a substituted stilbene unit into the terpyridine motif generates an intraligand charge-transfer-sensitive module whose absorption and emission spectral properties are highly sensitive to light as well as cations. On the basis of the optical response profile of the receptor in the presence of selected cations as well as light of a specific wavelength, we are able to demonstrate multiple Boolean logic functions such as INHIBIT, IMPLICATION, OR, NOR, and NAND, as well as various combinations of them. Of particular interest, we utilized the present system for the construction of security keypad locks and memory devices by maintaining a proper sequence of the stimuli and monitoring either absorption or emission spectral response at a specific wavelength as the output signal. In addition to various Boolean logic functions, the present system has also the ability to mimic fuzzy logic operations for generating an infinite-valued logic scheme depending on its emission spectral responses upon varying the concentration of cationic (Fe2+ and/or Zn2+) and anionic (CN-) inputs.

A Track-Based Molecular Synthesizer that Builds a Single-Sequence Oligomer through Iterative Carbon-Carbon Bond Formation

Summary We report an artificial molecular machine that moves along a track, iteratively joining building blocks to form an oligomer of single sequence with a continuous backbone of carbon-carbon bonds. The rotaxane features a macrocycle bearing an aldehyde-terminated chain and an axle containing different phosphonium ylides separated by rigid spacers. Each ylide is large enough to block the passage of the macrocycle, trapping the ring between the stopper at the terminus of original threading and the next ylide along the track. Once a building block is reachable, it is removed from the track through a Wittig reaction that adds it to the terminus of the growing chain. Operation on a four-barrier tetra(phosphonium salt) track produces a tetra(diphenylpropane) of single sequence linked through alkene bonds. The prototype extends the principle for molecular machines that build polymers by moving along tracks to the synthesis of sequence-encoded chains with continuous carbon backbones.

The Leap from Organic Light-Emitting Diodes to Organic Semiconductor Laser Diodes

In recent years, organic light-emitting device technology has expanded from organic light-emitting diodes (OLEDs) to organic semiconductor laser diodes (OSLDs) with the progress of sophisticated mo...

Stilbenes with Potent Protein Tyrosine Phosphatase-1B Inhibitory Activity from the Roots of Polygonum multiflorum

Seven new stilbene glycosides including three dimers (1-3) and four monomers (4-7) were isolated from the roots of Polygonum multiflorum along with nine previously identified stilbenes (8-16). In addition, two deglucosylated stilbenes, 2a and 3a, were also obtained as new dimeric stilbenes. The structures of the purified phytochemicals were elucidated by interpreting their spectroscopic data (NMR, HRMS, and ECD). To the best of our knowledge, this represents the first isolation of a phenylpropanoid (C6-C3) substituted with a stilbene unit (7) from the Polygonaceae family. In an in vitro enzyme assay with human recombinant protein tyrosine phosphatase-1B (PTP1B), compounds 2-5 showed weak PTP1B inhibition with an IC50 value range of 27.4-37.6 μM, while three deglucosylated stilbenes 2a, 3a, and 8a exhibited IC50 values of 2.1, 1.9, and 12.1 μM, respectively. The inhibition modes and binding mechanism of selected inhibitors (2a and 3a) were investigated using kinetic methods and molecular docking simulations.

Supramolecular gels derived from nucleoside based bolaamphiphiles as a light-sensitive soft material.

Light-sensitive Low Molecular Weight Gelators (LMWGs) derived from glyconucleoside bolaamphiphiles containing a stilbene unit displayed gelation abilities in hydroalcoholic mixtures. These materials showed a gel-sol transition under UV irradiation thanks to E-Z isomerization of stilbene and could find potential applications as drug delivery systems.

Effect of ring rize on photoisomerization properties of stiff stilbene macrocycles.

A series of stiff stilbene macrocycles have been studied to investigate the possible impact of the macrocycle ring size on their photodynamic properties. The results show that reducing the ring size counteracts the photoisomerization ability of the macrocycles. However, even the smallest macrocycle studied (stiff stilbene subunits linked by a six carbon chain) showed some degree of isomerization when irradiated. DFT calculations of the energy differences between the E- and Z-isomers show the same trend as the experimental results. Interestingly the DFT study highlights that the energy difference between the E- and Z-isomers of even the largest macrocycle (linked by a twelve carbon chain) is significantly higher than that of the stiff stilbene unit itself. In general, it is indicated that addition of even a flexible chain to the stiff stilbene unit may significantly affect its photochemical properties and increase the photostability of the resulting macrocycle.

Solvent-Free Photoresponsive Artificial Muscles Rapidly Driven by Molecular Machines.

We prepared photoresponsive actuators as both hydrogels and dry gels consisting of 4-arm poly(ethylene glycol) (PEG) cross-linked by a [c2]daisy chain, which is a double-threaded [2]rotaxane dimer with α-cyclodextrin (αCD) and stilbene. The obtained gels showed fast and large deformation triggered by UV irradiation in both wet and dry states. The UV/vis spectroscopy results, NMR measurements and tensile tests on the gels revealed that the actuation is driven by photoisomerization of the stilbene unit in the [c2]daisy chain. The responsiveness of these gels depends on the molecular weight of the 4-arm PEG. These results suggest that αCD recognizes trans-stilbene prior to UV irradiation to maintain the length of the PEG chain in the polymer network and that photoisomerization allows αCD to leave the cis-stilbene moiety and move onto the PEG chain because the association constant of αCD with cis-stilbene is quite low. Thus, the sliding motion of the αCD unit shrinks the [c2]daisy chain, leading to the contraction of the gels. In both wet and dry states, these actuations are repeatable through reversible photoisomerization of the stilbene moiety using different wavelengths of UV-light irradiation and can be used to perform bending and lifting actions (for 15 times heavier weight compared to the dry gel).

Cyanostilbene-Based Supramolecular Polymerization from One-Dimensional to Two-Dimensional Nanostructures via Photoreactions

Stilbene units are extensively used as supramolecular polymer substructures and key light-responsive components whose structures and/or functions are controllable via photochemical reactions. A stilbene unit was used to control the morphologies and properties of supramolecular polymerization via ultraviolet (UV) light. A cyanostilbene-based derivative revealed one-dimensional supramolecular polymerization with J-aggregates in methylcyclohexane, leading to a strong emission. Supramolecular polymerization follows the cooperative nucleation–elongation mechanism. Most importantly, the 1D supramolecular polymer was irradiated by UV light and underwent intermolecular [2 + 2] cycloaddition to produce a two-dimensional sheet structure. Additionally, the thermodynamic parameters of the UV-exposed aggregates were approximately 1.5-fold smaller than those of the nonexposed aggregates. These results demonstrate the utility of such stilbene-based aggregates in case of customizable supramolecular polymerization with UV...

Fluorescent star ATRP initiators and fluorescent star poly(methyl methacrylate)s: Synthesis and photophysical properties

Fluorescent star ATRP initiators containing four and six initiating sites, comprised with stilbene and α-cynostilbene units were synthesized and their photophysical properties were studied thoroughly. These multifunctional ATRP initiators showed solvatochromism. The dipole moment difference between ground state and excited state of the molecules were calculated using Lippert-Mataga equation and found that the molecules were more polar at excited state. The absorption coefficient, absorption and emission wavelength of the initiators prepared with α-cyanostilbene unit were found high compared to that prepared without -CN substituent. On the other hand, fluorescent lifetime of α-cyanostilbene based initiators was found low. The optical band gap energy calculated for the initiators were considerably low in the range of 2.56 eV–2.83 eV. Based on the photophysical properties, the hexa functional ATRP initiator containing α-cyanostilbene unit was used for ATRP of methyl methacrylate monomer to prepare fluorescent star PMMA; CuBr/PMDETA and CuBr/2,2′-bpy were used as catalysts. The molecular weight of star PMMAs ranged between 1.79 × 104 g/mol and 8.42 × 104 g/mol and the polydispersity index were in the range of 1.12–1.48. The linear increase of molecular weight against the monomer conversion indicated the living nature of polymerization. The absorption and emission spectra of polymer solution and film, and observation of polymer in bulk under UV light confirmed the polymer as green fluorescent; the average fluorescence lifetime of the polymer was found to be 0.92 ns.

Synthesis of silicon-containing macrocyclic compounds by using intramolecular [2+2] photocycloaddition reactions of bis-dimethylsilyl-linked styrenes and stilbenes

A method for the synthesis of silicon-containing macrocyclic compounds, using intramolecular [2 + 2] photocycloaddition reactions of bis-dimethylsilyl-linked styrene or stilbene derivatives, is described. Photoirradiation of benzene solutions of o- and m-bis(dimethylsilylmethyl)benzene derivatives, containing two styrene units, promotes efficient formation of intramolecular [2 + 2] photocycloadducts. In contrast, photoreaction of the corresponding para-substituted analog generates only dimers. Photoreactions of bis(dimethylsilylmethyl)benzene derivatives, possessing two stilbene units produce intramolecular [2 + 2] photocycloadducts along with products of cis-trans photoisomerization. The efficiencies of these intramolecular photoreactions depend on the distances between two double bonds undergoing [2 + 2] cycloaddition. Triplet-sensitized photoreactions of the stilbene derivatives lead to cis-trans isomerization exclusively. Finally, photoreactions of the stilbene derivatives in the presence of molecular oxygen produce phenanthrene derivatives as side products.