Stilbene-like Molecules Research Articles

Direct prediction of the solid-state fluorescence wavelength of 1-furyl/thienyl-2-arylethylene with the push-pull effect determined by NMR

Although it is known that push-pull effect of substituents affect the fluorescence emission of D-π-A molecules, the quantitative relationship between the push-pull effect and the fluorescence emission wavelength Em (or wavenumber νem) has not been reported up to now. Here we report the direct predicting the solid-state fluorescence wavelength of a kind of D-π-A molecules via using the push-pull effect of substituents determined by NMR. Starting from the stilbene-like molecules, 1-furyl/thienyl-2-arylethylene XCH = CHArY (abbreviated XAEY), the push-pull effect were determined via the chemical shifts difference ΔδC of the carbon in bridging bond CHCH. Then the solid-state fluorescence wavenumber νem of XAEY were correlated to the push-pull effect. The results show: (1) The νem of XAEY can be directly predicted with the push-pull effect ΔδC of the substituents. (2) The influence of ΔδC originating from para-Y on the νem is different from that of ΔδC originating from meta-Y on the νem. (3) Compared with the para-Y, the influence of the ΔδC of meta-Y on the νem is more potent.

Quantum Chemistry Calculation-Aided Structural Optimization of Combretastatin A-4-like Tubulin Polymerization Inhibitors: Improved Stability and Biological Activity

A potent combretastatin A-4 (CA-4) like tubulin polymerization inhibitor 22b was found with strong antitumor activity previously. However, it easily undergoes cis-trans isomerization under natural light, and the resulting decrease in activity limits its further applications. In this study, we used quantum chemistry calculations to explore the molecular basis of its instability. Aided by the calculations, two rounds of structural optimization of 22b were conducted. Accelerated quantitative light stability testing confirmed that the stability of these designed compounds was significantly improved as predicted. Among them, compounds 1 and 3b displayed more potent inhibitory activity on tumor cell growth than 22b. In addition, the potent in vivo antitumor activity of compound 1 was confirmed. Quantum chemistry calculations were used in the optimization of stilbene-like molecules, providing new insight into stilbenoid optimization and important implications for the future development of novel CA-4-like tubulin polymerization inhibitors.

Isocratic chromatography of resveratrol and piceid after previous generation of fluorescent photoproducts: Wine analysis without sample preparation

Resveratrol and its 3-glucoside (piceid), are stilbene-like molecules produced by plants. Both of them are weakly fluorescent, but highly fluorescent compounds are obtained when their hydroethanolic solutions are UV-irradiated, which implies a substantial improvement in the sensitivity of analytical methods. Experimental design (central composite design) together with the response surface methodology have been used to find optimum conditions for the fast, sensitive, and precise chromatographic analysis (with isocratic elution) of resveratrol and piceid in wine samples. These compounds have been UV-transformed into their respective photoproducts, which have been separated in a C18 column (Novapack C(18) 150x3.9 mm, 4 microm) by isocratic elution, using a mobile phase made up of acetonitrile and 4.1 vol% aqueous acetic acid, 19:81 v/v, at a flow rate of 0.8 mL/min, and fluorimetrically detected at 364 nm (lambda(exc) = 260 nm). Detection limits (S/N = 3) are 0.29 and 0.28 microg/L for resveratrol and piceid, respectively. The method has been applied to the analysis of these compounds in wine samples without a clean-up step. The analysis is completed in only 20 min. The standard addition method has been applied to the analysis of a commercial red wine and average recoveries near 100% were obtained for resveratrol and piceid. Three wine pools were satisfactorily analysed by external calibration.

Stilbene-Like Molecules as Fluorescent Probes Applied for Monitoring of Polymerization Process

2-(p-N,N-dimethylaminostyryl)benzoxazole (OS), 2-(p-N,N-dimethylaminostyryl)-benzothiazole (SS) and 2-(p-N,N-dimethylaminostyryl)naphtiazole (PS) were prepared and their absorption and fluorescence spectra were measured in various solvents at room temperature. On the basis of the solvatochromic behavior the ground state (mu(g)) and excited state (mu(e)) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (mu(g) and mu(e)) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of the dielectric constant (epsilon) and refractive index (n) of applied solvents. The absorption spectra only slightly are affected by the solvent polarity in contrast to the fluorescence spectra that are highly solvatochromic and display a large Stokes shift. The analysis of the solvatochromic behavior of the fluorescence spectra as function of Deltaf (epsilon, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment change along with the strongly red-shifted fluorescence, as the solvent polarity is increased, demonstrate the formation of an intramolecular charge transfer state (ICT). Compounds under the study were used as fluorescence probes for monitoring the kinetics of polymerization. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate (MMA) and during photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA).

Excited-State Behavior of trans and cis Isomers of Stilbene and Stiff Stilbene: A TD-DFT Study

The first part of the isomerization path on the two lowest excited states of trans and cis isomers of stilbene and stiff stilbene is investigated by means of TD-PBE0 calculations in the gas phase and in heptane solution. Solvent effects are taken into account by the PCM model. The excited-state optimized structures and the computed absorption and emission frequencies are in good agreement with the available experimental results. In all of the examined compounds, the isomerization process before barrier crossing occurs on the HOMO --> LUMO bright state, whereas the role played by other single-excitation states appears negligible. The relative energy barriers on the isomerization paths are consistent with the experimental excited-state lifetimes, suggesting a unifying picture of the isomerization process in stilbene-like molecules.

Photoelectron Spectra, Electronic Structures, and Conformational Properties of Substituted 2-Styrylpyrroles

The UV photoelectron spectra of three pairs of cis/trans-isomers of 2-(2-methylstyryl)pyrroles (1-6) have been recorded and analysed, making use of density functional theory (DFT) calculations at the B3LYP level. Compounds 1 and 2 have no further substituents in the pyrrole ring. In the other compounds the pyrrole ring is substituted by a methyl group in the 1-(3,4) or 5-position (5,6). Twisted conformations were calculated for 1-6 in which the toluene ring is generally much more distorted from the plane of the central C=C double bond than the pyrrole ring. In the cis-isomers (2, 4, 6) the torsion angle of the toluene groups amounts to about 50 o, while in the trans-isomers (1, 3, 5) the torsional angle is only about half as large. The energy difference delta IP values of the ionization bands associated with the molecular orbitals (MOs) pi7 and pi3 is related to torsion. Calculated delta IP values are generally 5-10 % larger than the experimental values, indicating that torsional vibrations contribute to the apparent distortion of the molecules. The results clearly indicate that PE spectroscopy - in combination with high-level quantum chemical calculations - is a verasatile method to distinguish E/Z isomers of heterocyclic stilbene-like molecules.

Photoelectron Spectra, Electronic Structures, and Conformational Properties of (E)-Stilbene, Styrylthiophenes, and (Thienylethenyl)pyridines

The UV photoelectron spectra of two isomeric styrylthiophenes (5, 6) and six isomeric (thienylethenyl)pyridines (7−12) have been recorded and analyzed, making use of DFT Becke3LYP calculations. The spectra were compared with those of (E)-stilbene (1e) and the isomeric styrylpyridines (2−4), which are π-isoelectronic with 5−12. Using quantum chemical analyses, planar molecular structures were obtained for all these compounds. However, from the separation ΔIP of the ionization bands associated with the π7 and π3 MOs, it is possible to make a distinction between planar and twisted molecular structures. Accordingly in these compounds, 2-substituted pyridine rings and 3-substituted thiophene rings are nearly untwisted, whereas phenyl rings, 3- and 4-substituted pyridine, and 2-substituted thiophene rings are twisted to an extent similar to that in 1e. The apparent distortion of the molecules is probably caused by torsional vibrations, so that twisted average geometries correspond to planar equilibrium structures. The B3LYP data permit detailed conclusions to be drawn with regard to the conformational preferences of 2- and 3-substituted thiophene and pyridine rings in heterocyclic analogues of 1e, as well as the to relative stabilities of isomers 7−12. The results clearly indicate that PE spectroscopy is a powerful method for analysis of conformational properties of stilbene-like molecules.

Effect of pyridyl and thienyl groups on the excited state properties of stilbene-like molecules

The relaxation properties of the lowest excited states of singlet and triplet multiplicity of sometrans-stilbene-like molecules with two-ring or three-ring polycyclic groups containing nitrogen and sulphur heteroatoms have been studied by stationary and pulsed fluorimetric and photolytic techniques. The kinetic parameters of the competitive relaxation processes, derived from the measured quantum yields and lifetimes, have been compared with the corresponding values of the hydrocarbon analogues to have information on the heteroatom effect on the photoisomerization mechanism. Then, π* states introduced by the nitrogen atom can play a deactivating role, mainly through vibronic coupling and consequent internal conversion to the ground state. The heavy atom introduced with the thiophene ring favours the spin-orbit coupling and then the rate of intersystem crossing to the triplet manifold. In any case, the position of the heteroatom is an important factor affecting the nature of the lowest excited states and then the radiative and reactive behaviour of these compounds. The presence of polycondensed rings leads to a decrease in the quantum yield of photoisomerization to thecis isomers, as reported for the corresponding hydrocarbons, owing to an increase in the torsional energy barrier. The latter is drastically reduced in the polar solvents.

Stilbene-like molecules: sulfur- and selenium-heterosubstituted indolo[ 3,2-b]indoles

In a series of molecules based on indolo [ 3,2-b ] indole, the sulfur and selenium heteroderivatives exhibit signs of deviation from planarity on excitation. A simple model is proposed to explain the photophysical behavior. For stilbene-like molecules, the distortion can be treated in terms of the torsional motion about the central CC bond. The torsion may facilitate spin-orbit coupling between states of ππ ∗ character. Analysis of the electronic matrix elements and Franck-Condon factors responsible for the radiative and non-radiative transitions leads to predictions concerning the correlations between the different rate constants, which are in agreement with the experimental data.

Role of charge transfer interactions in photoreactions. VII: Exciplexes of stilbene-like molecules with electron acceptors

The fluorescence quenching of six trans diarylethylenes (stilbene, 1- and 2-styrylnaphthalene, two aza-analogues of the latter, and 9-styrylphenanthrene) by electron acceptors was studied in three solvents together with the effect of charge-transfer interaction on the trans → cis photoisomerization. The fluorescence of the exciplexes has a relatively high quantum yield in non-polar solvents. The induced isomerization has a quantum yield higher than the intrinsic value in all solvents, particularly in the case of 2-styrylnaphthalene and its 3′-pyridyl derivative. Laser flash photolysis measurements on 9-styrylphenanthrene allowed spectral and kinetic characterizations of the triplet intermediate. The effect of the acceptors is discussed and compared with that previously observed for similar diarylethylenes in the presence of amines as electron donors.

ChemInform Abstract: Phosphorescence of trans‐Stilbene, Stilbene Derivatives, and Stilbene‐Like Molecules at 77 K.

ChemInformVolume 20, Issue 24 Physical Organic Chemistry ChemInform Abstract: Phosphorescence of trans-Stilbene, Stilbene Derivatives, and Stilbene-Like Molecules at 77 K. H. + GOERNER, H. + GOERNER MPI Strahlenchem., D-4330 Muelheim/R.Search for more papers by this author H. + GOERNER, H. + GOERNER MPI Strahlenchem., D-4330 Muelheim/R.Search for more papers by this author First published: June 13, 1989 https://doi.org/10.1002/chin.198924050AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume20, Issue24June 13, 1989 RelatedInformation

Phosphorescence of trans-stilbene, stilbene derivatives, and stilbene-like molecules at 77 K

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhosphorescence of trans-stilbene, stilbene derivatives, and stilbene-like molecules at 77 KHelmut GoernerCite this: J. Phys. Chem. 1989, 93, 5, 1826–1832Publication Date (Print):March 1, 1989Publication History Published online1 May 2002Published inissue 1 March 1989https://doi.org/10.1021/j100342a027RIGHTS & PERMISSIONSArticle Views526Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (858 KB) Get e-Alerts

Absorption and emission anomalies in solutions of trans-azastilbenes and related compounds possibly caused by association

Absorption and emission anomalies have been investigated for trans-styrylpyridines, dipyridylethylenes, and some other aza-analogues of stilbene-like molecules in aliphatic hydrocarbon solvents at low temperatures. Fluorescence spectra, quantum yields, and lifetimes have been measured at different excitation and emission wavelengths. On cooling, the structured fluorescence spectrum of the monomer is gradually replaced by a new broad red-shifted band which becomes prominent when irradiation is carried out at the red tail of the absorption spectrum. Its intensity decay is multi-exponential and the measured lifetimes depend on both λex and λem, reflecting a continuum of new species of longer lifetime than the monomeric compounds. The extent of these anomalies depends on solvent, concentration, temperature, rate of cooling, and structure of the olefin. The emission spectra of the crystalline azastilbenes differ from the broadband emission which is tentatively assigned to association products with a more or less narrow size distribution.

Role of charge transfer interactions in photoreactions III: inorganic anion-induced intersystem crossing of stilbene-like molecules

The effect of halide and thiocyanate anions on the fluorescence and photoisomerization of trans-stilbene, styrylnaphthalenes and their monosubstituted aza analogues was studied in a 2:3 acetonitrile; water mixture. The quenching of the fluorescence depends on the oxidation potential of the perturbers and is generally accompanied by anion-induced population of the reactive triplet state of the fluorescers. The limiting induced quantum yield for the trans → cis photoisomerization in the triplet manifold reachrs its maximum value of about 0.5 for the iodine anion which has the best heavy atom and electron donor properties.

Photophysical and photochemical behaviour of stilbene-like molecules and their aza-analogues

Abstract

Role of charge-transfer interactions in photo reactions. 2. Exciplexes between stilbene-like molecules and amines

Role of charge-transfer interactions in photo reactions. 2. Exciplexes between stilbene-like molecules and amines

Cis-4,4'-Stilbenediols. Synthesis from dienestrol, structure, and photocyclization to dihydrophenanthrenes

Diels--Alder cycloaddition reactions between dienestrol or its diacetate and dienophiles maleic anhydride, 4-phenyl-1,2,4-triazoline-3,5-dione, dimethyl maleate, 1,4-naphthoquinone, and tetracyanoethylene yielded adducts representing 4,4'-stilbenediols with obligate cis configuration. These compounds are ideally suited for studying the photochemical conversion of stilbene-like molecules to dihydrophenanthrenes without interference from the trans-stilbene isomers. The structures and stereochemistry of the Diels--Alder adducts were established by detailed interpretation of their NMR and mass spectra. UV irradiation of the synthesized cis-stilbenes caused photocyclization to the respective 4a,4b-dihydrophenanthrenes without interfering side reactions and with quantum yields in excess of 0.85.