Pyrylium Research Articles

Synthesis of highly phenylene substituted p-phenylene oligomers from pyrylium salts

A transition metal free route to phenyl substituted oligophenylenes that tolerates halogens is described.

Many-Photon Dynamics of Photobleaching

A detailed dynamical theory of photobleaching by periodical sequences of laser pulses is presented. The theory is used for interpretation of recent experiments with pyrylium salts. Our simulations are based on first-principles simulations of photoabsorption cross-sections and on empirical rate constants. Two competitive channels of photobleaching, namely, photobleaching from the lowest excited singlet and triplet states and from higher excited states, are found to explain different intensity dependences of the photobleaching rates in different samples. The process includes two-photon excitation from the ground state to the first or second excited singlet states and one-photon excitation from the first singlet or triplet states to higher excited states. The fluorescence follows double-exponential dynamics with two characteristic times. The first and the shorter one is the equilibrium settling time between the ground and the lowest triplet states. The second characteristic time, the time of photobleaching, is responsible for the long-term dynamics. The effective rate of photobleaching from the first excited singlet and lowest triplet states depends differently on the irradiance in comparison with the photobleaching in higher states. The first channel is characterized by a quadratic intensity dependence in contrast to the second channel that shows a cubic dependence. The competition between these photobleaching channels is very sensitive to the rate constants as well as to the repetition rate, the pulse duration, and the peak intensity. The double-exponential decay of the fluorescence is explained by the spatial inhomogeneity of the light beam. The findings in this work are discussed in terms of the possibility of using many-photon-induced photobleaching for new three-dimensional read-write devices.

Pyrylium salts in the synthesis of 2-pyrazoline derivatives and earlier unknown substituted 3,3a,4,7-tetrahydropyrazolo[1,5-a]pyridin-7-ones

New 1,3,5-substituted 2-pyrazoline derivatives were synthesized from 2,6-diphenylpyrylium perchlorate and acylhydrazines. Method for the synthesis of earlier unknown 3,3a,4,7-tetrahydropyrazolo[1,5-a]pyridin-7-one derivatives from pyrylium salts and cyanoacetic acid hydrazide was proposed.

Easy synthesis of heterocyclic carbene complexes by activation of chalcogenopyrones and benzopyrones to pyrylium salts and subsequent addition of carbanion of methoxy(methyl)pentacarbonyltungsten carbene complex

Methylenechalcogenopyran and benzopyran Fischer carbene complexes are easily obtained from commercially available chalcogenopyrones or benzopyrones and carbanion of methoxy(methyl)carbene tungsten complex. The key of the heterocyclic carbene formation is the activation of the carbonyl group by alkylation with alkyl trifluoromethanesulfonate reagent.

Chemistry of 1,5-diketones: I. Halogenation of aryl-substituted pent-2-ene-1,5-diones, pentane-1,5-diones, and their fused analogs

Halogenation of 3-(4-methoxyphenyl)-1,5-diphenylpent-2-ene-1,5-dione, 3-(4-methoxyphenyl)-1,5-diphenylpentane-1,5-dione, and 2-[1-(4-methoxyphenyl)-3-oxo-3-phenylpropyl)-1,2,3,4-tetrahydroaphthalen-one with bromine, chlorine, and dichloro(phenyl)-λ3-iodane leads to formation of the corresponding monobromo-, dichloro-, or trichloro-substituted 1,5-diketones, depending on the conditions. Halogenation of the aliphatic chain and methoxyphenyl substituent can be accompanied by heterocyclization to give pyrylium salts.

Ring transformations of heterocyclic compounds. XXV. Phenanthrene aldehyde imines via ring transformation of pyrylium salts with methylenedihydroisoquinolines—A novel access to the phenanthrene skeleton

Abstractmagnified imageThe ring transformation of 2,4,6‐triarylpyrylium salts 1 with 2‐methylenedihydroisoquinolines 6, generated in situ from the related 2‐methylisoquinolinium salts 2, in the presence of bases is reported. Whereas the transformation of 1 with 2(6) and sodium methoxide in methanol leads to 2‐(2,4,6‐triarylphenyl)isoquinolinium salts, with sodium ethoxide in ethanol the aryl substituted phenanthrene‐9‐carbaldehyde imines 4 are obtained, the structure of which was confirmed by an X‐ray structure determination of the 1‐(4‐methylphenyl) substituted derivative. Acid catalyzed hydrolysis of the imines 4 gives rise to the parent phenanthrene aldehydes. The transformation 1 + 2(6) → 4 represents a novel access to the phenanthrene skeleton.

Involvement of triplet excited states in the electron transfer photodegradation of cinnamic acids using pyrylium and thiapyrylium salts as photocatalysts

The mechanistic pathway for degradation of cinnamic acids using 2,4,6-triphenylpyrylium as well as 2,4,6-triphenyl(thia)pyrylium salts (,) as solar photocatalysts has been unambiguously established. Results obtained in steady-state experiments have been correlated with time-resolved photophysical studies. High percentages of photodegradation (60-70%) were achieved when aqueous solutions of caffeic and ferulic acids (,) as model pollutants were submitted to irradiation in the presence of ,. Electron-transfer quenching of both the singlet and triplet excited states of , by , has been proved, and the quenching rate constants (close to diffusion control) have been determined. However, the percentages of singlet quenching by ,, even at relatively high concentrations of the model pollutants, is lower than 5%. In addition to this, growth of the signal corresponding to the pyranyl radical occurs in the microsecond timescale, incompatible with the singlet state as precursor. Thus, photodegradation of , mainly involves the triplet state of the photocatalysts.

Novel [4 + 2] Cycloaddition between Thiobenzophenone and Aryl-Substituted Alkenes via Photoinduced Electron Transfer

The [4+2] cycloaddition products between thiobenzophenone (1) and arylalkenes (2) were obtained in the presence of (thia)pyrylium salts (sensitizer=3 or 4) as electron transfer photosensitizers. Although both radical cations 1*+ and 2*+ are generated, only the former is involved in the process.

New Thermal Rearrangement of 2,4,6‐Triarylthio(seleno)pyrylium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Selective reactivity of diamino Fischer-type carbene complexes towards 2,6-disubstituted and 2,4,6-trisubstituted pyrylium salts and 2,4,6-trichloro-1,3,5-triazine

The synthesis of new amino Fischer-type carbene complexes 2a– d with amino-containing side chain is presented. The reaction of these complexes with 2,4,6-triarylpyrylium salts gave the corresponding pyridinium salt 4a, 4c– e as expected from the initial attack of the free amino group onto the pyrylium α-carbon. When using the 2,6-diphenylpyrylium salt, a γ-addition of the amino group occurred, leading – after an hydrogen migration and a ring opening step – to the new organometallic unsaturated aminoketone 5. Finally, the reactivity of the diaminocarbene 2b with 2,4,6-trichloro-1,3,5-triazine has been investigated. The new triazine 6 bearing a ferrocenylaminocarbene group was isolated.

Donor‐Functionalized Polydentate Pyrylium Salts and Phosphinines: Synthesis, Structural Characterization, and Photophysical Properties

A series of donor-functionalized pyrylium salts have been prepared by classical condensation reactions which were further converted into the corresponding thienyl- and pyridyl-substituted polydentate lambda(3)-phosphinines by reaction with P(SiMe(3))(3). Further chemical modification of these phosphorus heterocycles with Hg(OAc)(2) in the presence of methanol resulted in the formation of lambda(5)-phosphinines. The photophysical properties of a selected series of thienyl- and pyridyl-functionalized pyrylium salts, lambda(3)- and lambda(5)-phosphinines, were investigated and the results compared and supported by theoretical calculations on the DFT level. Significant fluorescence was observed for the pyrylium salts and lambda(5)-phosphinines. In contrast, the heteroaromatic substituted lambda(3)-phosphinines show very little emission which is consistent with the low oscillator strength predicted by DFT calculations for this pi-->pi* transition. Furthermore, all three classes of compounds show readily observable phosphorescence in solution, which was determined by time-gated detection at low temperature.

Synthesis and Mesophase Properties of Intraanular Functionized Shape-persistent Macrocycles Containing Dibenzo [fg, op] naphthacenes

On the basis of the C-C coupling reactions of dibenzo [fg, op] naphthacene bistriflate, which was obtained by the condensation of phenylacetates with 4-aryl-2,6-bis(2-bromo-4-methoxy-phenyl) pyrylium salts followed by palladium-catalyzed dehydrohalogenation, three shape-persistent macrocycles with dibenzonaphthacene corner pieces, a nanometer interior void, and intraanular oligoalkyl side groups were synthesized by the oxidative cyclization of the corresponding bisacetylenes under high-dilution conditions. Their thermotropic liquid crystalline properties were investigated by using polarizing microscopy and differential scanning calorimetry. All the three compounds showed nematic mesophases and belonged to discotic liquid crystals with inverted topology.

Diels-Alder reaction between indoles and cyclohexadienes photocatalyzed by a (thia)pyrylium salt

Diels-Alder reaction between indoles and cyclohexadienes photocatalyzed by a (thia)pyrylium salt

4-(p-Methylthio)phenyl-2,6-diphenyl phosphinine: The first X-ray crystal structure of a λ3-triaryl-phosphabenzene

The new donor functionalized methylthio-phosphabenzene 3 was synthesized by reaction of the corresponding pyrylium salt with P(SiMe3)3. This compound was characterized crystallographically, showing eight independent molecules in the asymmetric unit. 3 crystallized in the orthorhombic space group Pna21 (no. 33) with cell parameters a=48.3565(8) Å, b=7.64784(7) Å, c=40.8432(4) Å, V=15104.7(3) Å3. This result represents the first crystal structure analysis of a λ3-triaryl-phosphabenzene.

Polynuclear heterocyclic systems based on naphthalene-1,5-diol: I. Reaction of naphthalene-1,5-diol and its derivatives with β-dicarbonyl and α,β-unsaturated carbonyl compounds

Reactions of naphthalene-1,5-diol and its derivatives (5-methoxynaphthalen-1-ol, 2-bromo-5-methoxynaphthalen-1-ol, and 2,6-di-tert-butylnaphthalene-1,5-diol) with ethyl acetoacetate, acetylacetone, and p-methoxycinnamic acid under acidic conditions (HCl, HClO4, CF3CO2H) gave substituted benzo[h]-chromenes, naphtho[1,2-b]pyrylium salts, and 3,4-dihydrobenzo[h]chromenes, respectively. Possible mechanisms were proposed for the observed acid-catalyzed heterocyclizations.

New thermal rearrangement of 2,4,6-triarylthio(seleno)pyrylium salts

It is known that1—3 4H thio(seleno)pyrans and thio pyrylium salts can be oxidized into the corresponding aroylfurans, thiophenes, and selenophenes. In addition, when analyzing pyrylium, thiopyrylium, and seleno pyrylium perchlorates by the GC MS method, we have found that the mass spectra and retention times of the compounds under analysis are completely identical with those of aroylselenophenes, thiophenes, and furans.4 This is in conflict with the previous5 MS data for 2,4,6 tri phenylpyrylium perchlorate: analogous spectra have been explained by the specific character of fragmentation of the heteroaromatic cation.5 We have found that seleno(thio)pyrylium perchlorates 1—3 applied to alumina transform to the corresponding aroylselenophenes and thiophenes 4—6 (Scheme 1) in 42—65% yields on heating to 300 °C in an inert atmo sphere (the yields of crude products reached 85—95%; however, the content of impurities was 10 to 30% (GC MS data)).

Early Excited State Dynamics of 6-Styryl-Substituted Pyrylium Salts Exhibiting Dual Fluorescence

A series of 6-styryl-2,4-diphenylpyrylium salts exhibiting dual fluorescence has been investigated by fluorescence up-conversion in conjunction with quantum chemical calculations. The short-wavelength emission is due to an excited state localized on the pyrylium fragment and the long-wavelength emission arises from a charge-transfer state delocalized over the whole molecule. The two fluorescing states do not exhibit a precursor-successor relationship. The rise time of the short-wavelength fluorescence is smaller than 200 fs, and that of the long-wavelength emission depends on the electron-donating property of the styryl group substituent. The rise is almost prompt with the weaker donors but is slower, wavelength and viscosity dependent with the strongest electron-donating group. A model involving a S(2)/S(1) conical intersection is proposed to account for these observations.

Blue light‐emitting poly(p‐phenylenevinylene) derivative with oxadiazole and carbazole pendant groups

AbstractA blue light‐emitting statistical poly(p‐phenylenevinylene) (PPV) copolymer with hole‐transporting carbazole and electron‐transporting oxadiazole pendant groups attached to the kinked m‐terphenyl unit was prepared by Heck coupling between 1,4‐divinylbenzene and dibromides. The latter were synthesized through pyrylium salts. The polymer had optical band gap of 2.89 eV and emission maximum at 446 nm in THF solution and 434 nm in thin film. It showed a pure blue emission with no aggregates or excimers formed even in solid state because of the long and bulky pendant groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3842–3849, 2006

Lipophilic Pyrylium Salts in the Synthesis of Efficient Pyridinium-Based Cationic Lipids, Gemini Surfactants, and Lipophilic Oligomers for Gene Delivery

Several new classes of pyridinium cationic lipids were synthesized and tested as gene delivery agents. They were obtained through a procedure that generates simultaneously the heterocyclic ring and the positively charged nitrogen atom, using lipophilic pyrylium salts as key intermediates that react with primary amines, yielding pyridinium salts. The choice of the appropriately substituted primary amine, diamine or polyamine, allows the design of the shape of the final lipids, gemini surfactants, or lipophilic polycations. We report also a comprehensive structure-activity relationship study that identified the most efficient structural variables at the levels of the hydrophobic anchor, linker, and counterion for these classes of pyridinium cationic lipids. This study was also aimed at finding the best liposomal formulation for the new transfection agents.

A novel approach for analyzing open Z-scan experiments

In this work, a novel method for analyzing open Z-scan experiments is presented. It is based on the calculation of the nonlinear absorption parameter q directly from the transmittance measurements. Specifically, we have found an analytic formula describing the dependence of the parameter q on the normalized transmittance. The influence of noise has been studied and the method was proved robust even under conditions of relatively high noise. Extension to the general case of an elliptic Gaussian incident beam has also been realized. The technique has been experimentally tested by analyzing transmittance measurements obtained from a recently synthesized pyrylium salt, illuminated by a femtosecond laser system. The results are in very good agreement with those obtained by the standard Z-scan analysis, especially regarding the nonlinear absorption coefficient β.