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In advanced photonics, there is a growing interest in piezochromic luminescent materials that exhibit multicolor switching, driven by their potential applications in optical recording, memory, and sensors. Here, the piezochromic behavior of 2,4,6‐triphenylpyrylium tetrachloroferrate (Py‐FeCl4) under high pressures from 0 to 9 GPa is reported. The observed multicolor changing properties of Py‐FeCl4 (yellow–orange–red–maroon–black) are found to be fully reversible upon decompression to ambient conditions. The mechanism of Py‐FeCl4 piezochromism is investigated via Raman, infrared, and UV–vis spectroscopy combined with powder X‐ray Diffraction. The absence of structural phase transitions as well as the abrupt shifts of bandgap values together with characteristic Raman and IR peaks within 0‐9 GPa suggests that the Py‐FeCl4 multicoloring switching behavior is driven by an electron transfer between the inorganic FeCl4− anion and the organic pyrylium cation. The obtained results demonstrate that Py‐FeCl4 dye is a good candidate for developing high‐pressure sensing technologies designed to function in extreme environments. Moreover, due to the inherent role of molecular‐structure relationships in the pyrylium salt's photophysical properties, findings suggest the potential discovery of piezochromic behavior in other pyrylium compounds. [ABSTRACT FROM AUTHOR]

We report a near‐IR fluorescence turn‐on chemosensing system for the selective detection of HSO4− anion in aqueous media. This system utilizes the equilibrium between the fluorescent pyrylium salt and its non‐fluorescent diketone form. The pyrylium compound we synthesized (λflo=674 nm) rapidly converts to its diketone form in the aqueous medium (ethanol‐water 4 : 1). HSO4− anion provides proton to diketone form inducing its conversion to pyrylium. Therefore, the sensor system responds to the presence of HSO4− by an increase in fluorescence. The change in the fluorescence increase is linear within the 20–55 μM range with a limit of detection of 12.8 μM. The system demonstrates high selectivity for HSO4− over other anions, as validated through fluorimetric titration studies. Additionally, interference studies highlight the minimal impact of common anions on bisulfate detection. Reversibility tests reveal the pronounced reversibility of the sensor system, with over 90 % recovery of fluorescence intensity achieved in subsequent iterations. [ABSTRACT FROM AUTHOR]

Pyrylium compounds are structures based on an oxonium heterocycle that has been extensively studied thanks to their superior absorption and fluorescence properties. In this study, pyrylium salts were first shown to be obtained in the solvent-free medium. Six pyrylium compounds, three of which were novel, were synthesized using this method. These compounds have different auxochromes on the phenyl groups at the 2,4 and 6 positions. In the final step, the photophysical properties of these compounds were examined and the effects of basic auxochromes on pyrylium photophysics were revealed. [ABSTRACT FROM AUTHOR]

• Pyrylium compound bearing auxochromes has been synthesized as a chemosensor. • The reactions of the chemosensor with each analyte yield different products with different photophysical properties. • Using the chemosensor, cyanide, propylamine, ammonia, and hydrazine can be discriminated from each other. Pyrylium salts are well known to react with different nucleophiles to form many different types of products like pyridinium salt, pyridine, cyanodienone, thiopyrylium, isoxazoline, N-aminopyridinium salt or 1,2-diazepine, depending on the nucleophile used. This property of pyrylium salts could be used to develop a multi-analyte chemosensor for the species having nucleophilic character. On this idea, we synthesized a pyrylium compound (PyrSen) bearing auxochromes and studied its photophysical responses to different nucleophiles. Different absorption spectra were observed to emerge upon the separate addition of cyanide, propylamine, ammonia, and hydrazine to the aqueous solution of PyrSen (ethanol-water 5:1). In the solutions containing ammonia and hydrazine were also observed fluorescence at different wavelengths. The products responsible for these photophysical properties were isolated and characterized. The developed sensor was proved to be usable for the discrimination and quantification of these four species in aqueous solutions. [ABSTRACT FROM AUTHOR]

The photophysical properties of molecular layers on dielectric support are studied for two pyrylium compounds, characterized by the presence or absence of a long styrene fragment in a molecule. It is shown that in the absence of a styrene fragment the layer absorption spectrum is significantly broadened in comparison with the spectrum of the solution of the starting compound and the Stokes shift is increased fivefold owing to a long-wavelength shift in the fluorescence maximum. Exposure of the layers to a high-power laser radiation also leads to a long-wavelength shift of the fluorescence spectrum and shows that the molecular layers exhibit high photoresistance compared to solutions of the same compounds. The orientation angles of the absorption transition dipole moments in the molecules of pyrylium compounds are estimated and change in the orientation angles in the course of successive irradiations by a series of nanosecond laser pulses is determined. [ABSTRACT FROM AUTHOR]

Pyrylium dyes having the same basic chemical structure, differing only to a specific substituent, have been used as novel materials for multiphoton three-dimensional data storage. Electronic absorption spectra, two-photon and three-photon absorption properties of this class of pyrylium dyes, have been studied theoretically and compared to experimental results. The effects of the counteranion, the surrounding solvent, and electron releasing and electron withdrawing groups in specific positions of the basic structure have been explored in detail. It is argued that on grounds of the quality of experimental spectroscopic agreement, the computed two- and three-photon data may be used in pulse propagation simulations of three-dimensional recording in optical memories. [ABSTRACT FROM AUTHOR]

A general and highly enantioselective synthesis of oxygen heterocycles from readily available in situ generated pyrylium derivatives has been realized by embracing a multi‐coordination approach with helical anion‐binding tetrakistriazole catalysts. The high activity of the tetrakistriazole (TetraTri) catalysts, with distinct confined anion‐binding pockets, allows for remarkably low catalyst loadings (down to 0.05 mol %), while providing a simple access to chiral chromanones and dihydropyrones in high enantioselectivities (up to 98:2 e.r.). Moreover, experimental and theoretical studies provide new insights into the hydrogen‐donor ability and key binding interactions of the TetraTri catalysts and its host:guest complexes, suggesting the formation of a 1:3 species. CApTive lock‐key model: Oxygen heterocycles were synthesized in high enantioselectivities from pyrylium derivatives by embracing a multi‐coordination approach with helical anion‐binding tetrakistriazole catalysts. New insights into the hydrogen‐donor ability and key binding interactions suggest the formation of a high‐order host:guest complex. [ABSTRACT FROM AUTHOR]

A convergent approach allowed total synthesis of (±)‐Englerin A, and its truncated analogues, employing a thermal 1,3‐dipolar cycloaddition of a highly substituted pyrylium ylide with vinyl acetate as the key step. The key intermediate, a 8‐oxabicyclo[3,2,1]octane oxygenated at the C6 position, was directly converted into a truncated Englerin A analogue. CuI catalyzed conjugate addition of vinyl Grignard to an enone, ozonolysis, and epimerisation of the resulting aldehyde allowed stereoselective introduction of the side‐chain leading to a total synthesis of the racemic natural product. The developed chemistry will allow synthesis of more complex analogues of the natural product based on the use of the key bicyclo[3,2,1]octane scaffold. Total synthesis of (±)‐Englerin A and a number of truncated analogues was developed based on a 1,3‐dipolar cycloaddition of a substituted pyrylium ylide. The bicyclic enone scaffold was further converted into a truncated analogue and the natural product. Interesting stereochemical effects of the bridgehead substituents on the reactivity of the 8‐oxabicyclo[3.2.1]octanes were uncovered. [ABSTRACT FROM AUTHOR]

Abstract Enzymatic 18O exchange, the well-established approach in comparative proteomics, has some disadvantages such as back exchange of labeled oxygen and overlapping the peak of a labeled peptide with isotopic peaks of an unlabeled one. Herein we demonstrated a simple procedure in which samples digested with a trypsin (with and without H 2 18O) were reacted with unlabeled and quadrupled 13C-labeled pyrylium salt respectively which results in formation of pyridinium cations. Thus, each isobarically labeled peptide containing zero or four 13C atoms in the mass reporter group, during tandem MS/MS forms an unique reporter ion useful for a relative quantitation. Such a sample treatment improves the signal to noise ratio, reduces overlapping of the isotopic peaks and completely eliminates the back exchange problem. Graphical abstract Image 1 Highlights • Formation of the isobaric peptides derivatives (duplex) in two samples compared. • A combination of enzymatic incorporation of 18O and reaction with 13C pyrylium salt. • The MS/MS experiment generates diagnostic ions shifted by 4 Da. • It solves the problem of overlapping of the isotopic peaks in the 18O approach. • Method eliminates the risk of back-exchange and increase of the ionization efficiency. [ABSTRACT FROM AUTHOR]

Abstract Here, we discuss the formation of several heterocyclic benzopyrylium compounds via joint experimental-theoretical efforts, in order to obtaining a better understanding of the diverse properties of these interesting organic species. Our results suggest these benzopyrylium dyes as interesting sensitizers in the novel design of new solar cells from the basis of their optical properties and pH-dependent characteristics. The role of aromatic stability of the pyrylium compounds in the obtained properties is discussed in terms of both NBO and analysis of the induced magnetic field toward the isotropic respond. Furthermore, optical properties were analyzed in the framework of TD-DFT methodologies. Noteworthy changes in red-shift and absorptions λ max are observed that contribute toward the interesting DSSCs applications. Additionally, the emission profile of 2a derivative was obtained in agreement to both theoretically and experimental strategy. We expect that our results can be informative for further development of heterocyclic benzopyrylium compounds and their application in DSSCs devices. Graphical abstract Image 1 Highlights • Formation of benzopyrylium compounds via joint experimental-theoretical efforts. • Benzopyrylium dyes as interesting sensitizers in the novel design of new solar cells. • Optical properties were analyzed in the framework of TD-DFT methodologies. • Aromatic stability in terms of NBO and induced magnetic field to isotropic respond. [ABSTRACT FROM AUTHOR]

Resonant chalcogenpyrylium nanotags demonstrate an exceptional surface enhanced Raman scattering (SERS) performance for use in SORS applications. Using surface enhanced spatially offset Raman spectroscopy (SESORS), nanotags modified with a chalcogenpyrylium dye were observed at concentrations as low as 1 pM through 5 mm of tissue. Calculated limits of detection suggest that these SERS nanotags can be detected at 104 fM using surface enhanced spatially offset resonance Raman scattering (SESORRS) demonstrating their potential for in vivo applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Py-Tag allows quantification analysis due to wide mass differences of 6 Da using 13C. • Py-Tag as a new stable isotope tag can specifically react with primary amino groups. • Concurrent MS analysis of multiple samples is possible by both MALDI- and LC–MS. Abstract The quantification of amino acids, peptides and proteins are important in fundamental science to understand intravital event, as well as in applied fields such as biological, medical, and pharmaceutical sciences. Py-Tags (Py0, Py6 and Py12) are primary amine-reactive isotope-labelled tagging reagents. Py-Tags can selectively and efficiently react with the primary amino group which has more than a two-carbon chain from the alpha-carbon of the target sample by the reaction of pyrylium salts with nucleophiles under alkaline conditions, thereby increasing the mass by 175.15, 181.17, and 187.19 Da, respectively, and generating positive ions. We used Py-Tags to label not only the amino acids but also peptides with a lysine residue(s), fragment peptides with a lysine(s), digested proteins, and intact proteins. All Py-Tag-labelled peptide sets showed similar mass differences. Thus, we could easily analyze expression ratio by single measurement. Furthermore, the ratio of the measured ion intensities was representative of the relative amount of each material. [ABSTRACT FROM AUTHOR]

Electrochromism (electric-field-modulated absorption) spectra are reported for a thiapyrylium dye in a polycarbonate host. When the dye is homogeneously dissolved in the polymer, excitation to the first excited singlet state changes its dipole moment by approximately 6 D (2×10-29 C m). When the dye is aggregated with the host polymer, the structure of the aggregate is believed to consist of layer of the dye associated with layers of the polymer. The electrochromism spectrum indicates that the aggregate possesses two (or more) excitonic states separated by ∼450 cm-1, of which only the lower contributes to the absorption spectrum in the absence of an electric field; application of a field mixes and shifts these states and transfers intensity between them. The near degeneracy is believed to be a consequence of weak Davydov interactions between the exciton states of pairs (or larger stacks) of dye layers. [ABSTRACT FROM AUTHOR]

In this study, we developed a flatbed-scanner-based Cu 2+ -selective signaling method using a coumarin–benzopyrylium conjugated dye platform. The designed sensors ( CB-1 and CB-2 ) were readily synthesized by the reaction of coumarin–benzopyrylium hydrazide with salicylaldehyde or 2-hydroxynaphthaldehyde, respectively. Sensor CB-1 exhibited pronounced colorimetric and fluorescence signaling behaviors toward Cu 2+ ions in 50% aqueous acetate buffered (pH 4.7) acetonitrile solution. The Cu 2+ signaling of the developed sensor was not affected by the presence of environmentally relevant metal ions. The detection limit of sensor CB-1 for Cu 2+ ions was estimated to be 4.0 × 10 −8  M (2.5 ppb). In addition, to develop a convenient and straightforward Cu 2+ detection method for nonprofessional personnel and practical field applications, the colorimetric determination of Cu 2+ ions using a flatbed scanner, a readily available IT device, was investigated. Using simulated semiconductor wastewater as a practical sample, the Cu 2+ levels were readily determined by a flatbed scanner in transmittance mode with a sensitive detection limit of 2.9 × 10 −7  M (18 ppb). [ABSTRACT FROM AUTHOR]

Abstract: The functionalization of aminoheterocycles by using a pyrylium tetrafluoroborate reagent (Pyry‐BF4) is presented. This reagent efficiently condenses with a great variety of heterocyclic amines and primes the C−N bond for nucleophilic aromatic substitution. More than 60 examples for the formation of C−O, C−N, C−S, or C−SO2R bonds are disclosed herein. In contrast to C−N activation through diazotization and polyalkylation, this method is characterized by its mild conditions and impressive functional‐group tolerance. In addition to small‐molecule derivatization, Pyry‐BF4 allows the introduction of functional groups in a late‐stage fashion to furnish highly functionalized structures. [ABSTRACT FROM AUTHOR]

Advanced oxidation processes are useful methodologies to accomplish abatement of contaminants; however, elucidation of the reaction mechanisms is hampered by the difficult detection of the short-lived primary key species involved in the photocatalytic processes. Nevertheless, herein the combined use of an organic photocatalyst such as triphenylpyrylium (TPP + ) and photophysical techniques based on emission and absorption spectroscopy allowed monitoring the photocatalyst-derived short-lived intermediates. This methodology has been applied to the photocatalyzed degradation of different pollutants, such as acetaminophen, acetamiprid, caffeine and carbamazepine. First, photocatalytic degradation of a mixture of the pollutants showed that acetaminophen was the most easily photodegraded, followed by carbamazepine and caffeine, being the abatement of acetamiprid almost negligible. This process was accompanied by mineralization, as demonstrated by trapping of carbon dioxide using barium hydroxide. Then, emission spectroscopy measurements (steady-state and time-resolved fluorescence) allowed demonstrating quenching of the singlet excited state of TPP + . Laser flash photolysis experiments with absorption detection showed that oxidation of contaminants is accompanied by TPP + reduction, with formation of a pyranyl radical (TPP ), that constituted a fingerprint of the redox nature of the occurring process. The relative amounts of TPP detected was also correlated with the efficiency of the photodegradation process. [ABSTRACT FROM AUTHOR]

A series of substituted, pyridyl-functionalized 2,4,6-triarylpyrylium salts were prepared and investigated for their light absorption and emission properties. After reaction with P(SiMe3)3, the corresponding λ3-phosphinines were obtained, which carry on the 4- or 6-aryl ring ±I and ±M substituents. Supported by DFT calculations, a systematic evaluation of the σ-donor and π-donor as well as π-acceptor properties of these low-coordinate P,N-hybrid ligands was performed. The modular synthetic approach allowed us at the same time to synthesize the structurally related bipyridine derivatives for comparison reasons. Reaction of the chelating ligands with [W(CO)6] in THF afforded the corresponding [(P^N)W(CO)4] and [(N^N)W(CO)4] complexes. A crystallographic characterization of selected coordination compounds revealed significant structural differences between the pyridyl-phosphinine- and the bipyridine-based compounds. Their characterization by means of IR-spectroscopy gave experimental insight into the electronic properties of the respective ligands. [ABSTRACT FROM AUTHOR]

Abstract: Organocatalytic synthesis of bi‐ and tricyclic fused 1,2,4‐oxadiazolines is reported. The reaction proceeds through oxidative cyclization of the corresponding amidoxime using 2,4,6‐tris(4‐fluorophenyl)pyrylium tetrafluoroborate (T(p‐F)PPT) as the organocatalyst, and molecular oxygen as the green oxidant. During the transformation, T(p‐F)PPT acts as both the electrophilic catalyst and photocatalyst, and the reaction is promoted by irradiation with visible light. The method introduced herein offers a straightforward route to the preparation of 1,2,4‐oxadiazolines with different functionalities, and is highly atom economical. [ABSTRACT FROM AUTHOR]

Abstract: Gaining temporal control over chain growth is a key challenge in the enhancement of controlled living polymerizations. Though research on photocontrolled polymerizations is still in its infancy, it has already proven useful in the development of previously inaccessible materials. Photocontrol has now been extended to cationic polymerizations using 2,4,6‐triarylpyrylium salts as photocatalysts. Despite the ability to stop polymerization for a short time, monomer conversion was observed over long dark periods. Improved catalyst systems based on Ir complexes give optimal temporal control over chain growth. The excellent stability of these complexes and the ability to tune the excited and ground state redox potentials to regulate the number of monomer additions per cation formed allows polymerization to be halted for more than 20 hours. The excellent stability of these iridium catalysts in the presence of more nucleophilic species enables chain‐end functionalization of these polymers. [ABSTRACT FROM AUTHOR]

A novel symmetrical 2,10-bis-styryl-1-benzopyrylium dye was synthesized through two steps: In the first reaction an aldol condensation between 2,4,6-trihydroxybenzaldehyde and 3,4-dihydroxymethylstyrylketone gave 5,7,3',4'-tetrahydroxy-2-styryl-1-benzopyrylium; and in the second step this latter reacted with the same ketone by a cycloaddition reaction yielding the symmetrical 2,10-bis(3,4-dihydroxystyryl)- pyrano-7-hydroxy-1-benzopyrylium. The dye was fully characterized by LC-DAD/ESI-MS and NMR 1D and 2D techniques, and a formation pathway was proposed. The novel dye obtained revealed extended π-conjugation (λmax 556 nm) and catechol groups in its composition, which is very important for applications as a photosensitizer for dye-sensitive solar cells (DSSCs). [ABSTRACT FROM AUTHOR]

The following review article provides an overview of oxidopyrylium [5+2] cycloaddition chemistry, with a particular emphasis placed on seminal historical developments and advancements made over the last decade. It is our hope this review serves as a valuable resource to those interested in the oxidopyrylium cycloaddition chemistry, and helps inspire future advancements. [ABSTRACT FROM AUTHOR]

ABSTRACT: A dense membrane (MS) based on vinyl polymers and containing a pyrylium salt [2,6‐diphenyl‐4(p‐methacryloyloxy)phenylpyryliumtetrafluoroborate] was prepared. The MS has hydrophilic and sensory properties that make it a good material for the selective colorimetric detection of trimethylamine (TMA) vapors, a biogenic amine of great importance in food safety. The polymeric sensor changes from yellow to an intense pink color with increasing concentrations of TMA. The material could be reused in the presence of HCl vapors for at least 10 times. The detection and quantification limits were determined by ultraviolet–visible absorption spectroscopy (4.42 and 13.40 ppm, respectively) and by the RGB parameters of digital color (3.37 and10.22 ppm, respectively). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46185. [ABSTRACT FROM AUTHOR]

Ylide-type reactivity of diazo compounds is exploited in a new way to prepare benzo[b]oxepines thanks to the formation of three chemical bonds and two contiguous and highly substituted stereocenters in a single pot. This cationic reaction cascade first involves addition of a donor-acceptor-substituted diazo compound to a benzopyrylium. Selective 1,2 migration of the endocyclic C-C bond then results in a ring-expansion and generates a second oxocarbenium that is trapped by a nucleophile added sequentially. [ABSTRACT FROM AUTHOR]

A series of new pyrylium salts that bear sulfonate and phosphonate groups were obtained from the reactions between 2,6-diphenyl-4 H -pyran-4-one, sulfonic anhydride, and chlorophosphates, and analyzed spectroscopically. Furthermore, treatment of 2,6-diphenyl-4 H -pyran-4-one with phosphoryl chloride or bromide afforded the corresponding 4-chloro- and 4-bromopyrylium tetrafluoroborates in good yield. Subsequently, the synthesis of the corresponding 4-chloro- and 4-bromophosphinines was accomplished by treating the respective chloro- and bromopyrylium tetrafluoroborates with tris(trimethylsilyl)phosphine. [ABSTRACT FROM AUTHOR]

The first catalytic enantioselective [5 + 2] dipolar cycloaddition of a 3-hydroxy-4-pyrone-derived oxidopyrylium ylide is described. These studies leveraged the recently recognized ability of oxidopyrylium dimers to serve as the source of ylide, which was found to be key to increasing yields and achieving enantiomeric excesses up to 99%. General reaction conditions were identified for an array of α,β-unsaturated aldehyde dipolarophiles. Reaction products possess four stereocenters, and subsequent reduction introduced a fifth contiguous stereocenter with total stereocontrol. [ABSTRACT FROM AUTHOR]

Described herein is the synthesis of stable oxonium-doped polycyclic aromatic hydrocarbons (PAHs) by the rhodium-catalyzed C−H activation/annulations of naphthalene-type aldehydes with internal alkynes. This protocol provides four divergent reaction types, including two unexpected annulations with an oxygen transposition process, which lead to diverse types of phenalenyl-fused pyrylium cations comprising a four-, five-, or six-ring-fused π-conjugated core. The annulations exhibit an exquisite regioselectivity and a high tolerance of sensitive functional groups. These PAHs feature intriguing photophysical properties such as full-color tunable fluorescence emission, high quantum yield, and positively charged core, and can be reduced easily to the phenalenyl radicals. [ABSTRACT FROM AUTHOR]

An optical detection of volatile organic compounds (VOCs) using nanosized zeolites functionalized with pyrylium salts is presented. Nanosized zeolite crystals firstly are functionalized with pyrylium salt (para-dimethylamino-2,4,6-triphenylthiopyrylium tetrafluoroborate, PNS). Then the optical response of the pyrylium-functionalized nanozeolites towards volatile organic compounds is investigated. Two possible modes of zeolite functionalization are proposed based on: (1) ion exchange between the pyrylium and sodium cations (Na + ) in the zeolite (Si-O − -Al active sites), and (2) adsorption via electrostatic interaction between the electron lone-pair of amine of the PNS and the orbital vacancy of Al on the zeolite surface (Lewis acid sites). The experimental results verify that the great number of Lewis acid sites of the nanozeolites led to a significant adsorption of the PNS (mode 2) causing the hypsochromic (band shift to lower wavelength) shift in the visible light absorbance. Pyrylium-functionalized nanozeolites demonstrate a good sensitivity and reversibility toward volatile organic compounds investigated in this work. [ABSTRACT FROM AUTHOR]

We present here a complete study on four synthetic environmentally friendly flavylium salts employed as sensitizers for dye-sensitized solar cells (DSSCs). The effect of several donor groups on the molecular structure of flavylium ions was investigated by combining electrochemical, spectroscopic and computational means. The computational investigation indicated that these molecules can interact strongly with the TiO2 surface by a single OH group of the dihydroxybenzene moiety, and can efficiently inject electrons into the TiO2 following the excitation of their lowest singlet states exhibiting charge transfer (CT) character. In general, all dyes within the explored series exhibited quite good regeneration efficiencies, often ≥70%, in the presence of an iodide electron donor, explaining the high IPCEs and photocurrents recorded in the presence of high lithium content electrolytes. The combination of molecular orbital calculations and electrochemical measurements has also revealed that the introduction of donor groups on the benzopyrylium ring has a generally positive effect resulting in an extended low energy light harvesting and in a potential improvement of the photoinduced charge separation at the semiconductor/dye/electrolyte interface. It also increases the reversibility of the oxidative redox processes of these bio-inspired species, a feature in favour of their long-term stability. At present the best dye within the explored series is 7-(N,N-diethylamino)-3′,4′-dihydroxyflavylium chloride based on a dialkylamine donor which is capable of delivering, under optimized conditions, a short-circuit current density of 15 mA cm−2. This is the highest value so far obtained for synthetic analogues of anthocyanins. [ABSTRACT FROM AUTHOR]

Density functional theory calculations were carried out in order to determine the viability of putative mechanistic pathways for formation of the diterpenoid (+)-chatancin. It was found that a cycloaddition involving a pyrylium ion would have a lower energetic barrier than previously proposed cycloadditions involving a 2H-pyran or furan. All three reactions are predicted to be concerted. [ABSTRACT FROM AUTHOR]

Pyrylium salts combined with vinyl ethers are shown to act as new versatile dual-cure initiating systems for both photochemical and thermal initiation of oxirane monomers. The combination of both possibilities allows the curing of thick samples through photoinduced frontal polymerization. On the basis of quantum calculations and photochemical experiments, some clues are given about the reaction mechanisms involved. Interestingly, a sequential kick-starting effect is observed in the presence of vinyl ether enabling the curing of oxetane monomers. Thereby, this communication presents a short overview of potential of pyrylium salts in cationic polymerization of oxiranes. [ABSTRACT FROM AUTHOR]

We report the exploration into photoredox generation of carbonyl ylides from benzylic epoxides using newly designed 4-mesityl-2,6-diphenylpyrylium tetrafluoroborate (MDPT) and 4-mesityl-2,6-di-p-tolylpyrylium tetrafluoroborate (MD(p-tolyl)PT) catalysts. These catalysts are excited at visible wavelengths, are highly robust, and exhibit some of the highest oxidation potentials reported. Their utility was demonstrated in the mild and efficient generation of carbonyl ylides from benzylic epoxides that otherwise could not be carried out by current common photoredox catalysts. [ABSTRACT FROM AUTHOR]

The effects of oxygen addition on a helium-based flowing atmospheric pressure afterglow (FAPA) ionization source are explored. Small amounts of oxygen doped into the helium discharge gas resulted in an increase in abundance of protonated water clusters by at least three times. A corresponding increase in protonated analyte signal was also observed for small polar analytes, such as methanol and acetone. Meanwhile, most other reagent ions (e.g., O , NO, etc.) significantly decrease in abundance with even 0.1% v/v oxygen in the discharge gas. Interestingly, when analytes that contained aromatic constituents were subjected to a He:O-FAPA, a unique (M + 3) ion resulted, while molecular or protonated molecular ions were rarely detected. Exact-mass measurements revealed that these (M + 3) ions correspond to (M - CH + O), with the most likely structure being pyrylium. Presence of pyrylium-based ions was further confirmed by tandem mass spectrometry of the (M + 3) ion compared with that of a commercially available salt. Lastly, rapid and efficient production of pyrylium in the gas phase was used to convert benzene into pyridine. Though this pyrylium-formation reaction has not been shown before, the reaction is rapid and efficient. Potential reactant species, which could lead to pyrylium formation, were determined from reagent-ion mass spectra. Thermodynamic evaluation of reaction pathways was aided by calculation of the formation enthalpy for pyrylium, which was found to be 689.8 kJ/mol. Based on these results, we propose that this reaction is initiated by ionized ozone (O ), proceeds similarly to ozonolysis, and results in the neutral loss of the stable CHO radical. [ABSTRACT FROM AUTHOR]

The synthesis of pyrylium and pyridinium salts and pyridines with azulene-1-yl moieties in position 4 and two 2-heteroarylvinyl groups in positions 2 and 6 was accomplished. The pyrylium salts were obtained starting from pyranones and pyridines could be prepared from these salts by treating them with ammonium acetate. The general procedures for the synthesis of pyridinium salts, which occur with good results in less delocalized electronic systems, do not take place when applied to the above obtained pyrylium salts. Therefore, as starting material 4-(azulen-1-yl)-1-(n-butyl)-2,6-dimethylpyridinium perchlorate was used, which was condensed with heteroarylcarboxaldehydes. These compounds were completely characterized and some of their spectra were discussed. Their interaction with some metal ions was revealed, observing an affinity better than in the case of simple azulenepyridines. In the last part of the paper are presented redox potentials for several pyrylium salts and pyridines in comparison with those of the nonvinylogated derivatives. [ABSTRACT FROM AUTHOR]

An unprecedented Rh-catalyzed ketone-directed vinylic C−H activation/[4+2] O-annulation of α-aryl enones with internal alkynes followed by a Cu-catalyzed ring contraction in air to provide multiaryl-substituted furan derivatives has been developed. The preliminary mechanism study identifies the active pyrylium salt as the key intermediate. [ABSTRACT FROM AUTHOR]

4-Ethyl-3-formyl-2,6-diphenylpyrylium perchlorate was obtained from 2,6-diphenylpyrylium perchlorate in three steps. Its reaction with triethyl orthoformate was accompanied by rearrangement of the initial pyrylium ring and led to pyrano[3,4- c]pyran-7-ium perchlorate system through a domino process involving ethanol addition-elimination. A plausible mechanism of the reaction is suggested on the basis of DFT quantum-chemical calculations. Reaction of the obtained pyrano[3,4- c]pyran-7-ium perchlorate with ammonium acetate led to a 2,7-naphthyridine derivative without a skeletal rearrangement. [ABSTRACT FROM AUTHOR]

A model for simulating the transient electronic absorption spectra of donor-acceptor dyads undergoing ultrafast intramolecular charge transfer in solution has been developed. It is based on the stochastic multichannel point-transition approach and includes the reorganization of high-frequency intramolecular modes (treated quantum mechanically) and of low frequency intramolecular and solvent modes (described classically). The relaxation of the slow modes is assumed to be exponential with time constants taken from experiments. The excited-state dynamics is obtained by simulating the population distribution of each quantum state after optical excitation and upon electronic and vibrational transitions. This model was used to simulate the transient electronic absorption spectra measured previously with a pyrylium phenolate in acetonitrile. A very good agreement between the simulated and measured spectra was obtained assuming a three-level model including the ground state, the optically excited state, and a dark state with large charge-transfer character and a substantially different geometry relative to that of the optically excited state. The merit of this approach to disentangle the contributions of both population changes and relaxation processes to the ultrafast spectral dynamics will be discussed. [ABSTRACT FROM AUTHOR]

Recently we described a novel di-benzene-pyrylium-indolene (BAS00127538) inhibitor of Lipid II. BAS00127538 (1-Methyl-2,4-diphenyl-6-((1E,3E)-3-(1,3,3-trimethylindolin-2-ylidene)prop-1-en-1-yl)pyryl-1-ium) tetrafluoroborate is the first small molecule Lipid II inhibitor and is structurally distinct from natural agents that bind Lipid II, such as vancomycin. Here, we describe the synthesis and biological evaluation of 50 new analogs of BAS00127538 designed to explore the structure-activity relationships of the scaffold. The results of this study indicate an activity map of the scaffold, identifying regions that are critical to cytotoxicity, Lipid II binding and range of anti-bacterial action. One compound, 6jc48-1, showed significantly enhanced drug-like properties compared to BAS00127538. 6jc48-1 has reduced cytotoxicity, while retaining specific Lipid II binding and activity against Enterococcus spp. in vitro and in vivo. Further, this compound showed a markedly improved pharmacokinetic profile with a half-life of over 13 hours upon intravenous and oral administration and was stable in plasma. These results suggest that scaffolds like that of 6jc48-1 can be developed into small molecule antibiotic drugs that target Lipid II. [ABSTRACT FROM AUTHOR]

Chalcogenopyrylium nanotags demonstrate an unprecedented SERS performance with a retina safe, 1550 nm laser excitation. These unique nanotags consisting of chalcogenopyrylium dyes and 100 nm gold nanoparticles produce exceptional SERS signals with picomolar detection limits obtained at this extremely red-shifted and eye-safe laser excitation. [ABSTRACT FROM AUTHOR]

Pyrylium salts are found to be effective initiators for both photochemical and thermal cationic polymerization of epoxy resin. The photopolymerization results show that triphenylpyrylium salt derivatives are the most efficient structures. These compounds also exhibit some thermal reactivity at room temperature in the absence of light. However in such case, the gel time of the resin is quite high. Therefore, to speed up the thermal reaction, nucleophilic compounds are added as coinitiators, these compounds being known to yield a fast decomposition of pyrylium salts. This indeed increases the polymerization of epoxy resin at room temperature, opening the way to the development of quite efficient dual-cure photochemical/thermal initiating system for cationic polymerization. [ABSTRACT FROM AUTHOR]

Treatment of methyl (Z)-2-alken-4-ynoates with the strong Lewis acid tris(pentafluorophenyl) borane, B(C6F5)3, yield substituted zwitterionic pyrylium borate species via an intramolecular 6-endo-dig cyclisation reaction. [ABSTRACT FROM AUTHOR]

The crystal structure of a co-crystal of 2,4,6-tris(4-methylphenyl)pyridine and 2,4,6-tris(4-methylphenyl)pyrylium revealed a pseudohexagonal motif assembled from π-stacked helices that enclose 1-D channels containing disordered tetrafluoroborate counterions and solvent molecules. Though convoluted by disorder, aperiodicity, and complex twinning patterns, further investigation was motivated by the unique packing arrangement of this material, which enables solid-state anion diffusion, while resisting dissolution in water. Such properties are ideal for the development of anion exchange materials that can be employed for the remediation of agricultural and nuclear waste. To develop a more complete understanding of the intermolecular interactions that give rise to this helical motif, we have compiled and analyzed the local interactions and extended structural motifs of 19 pore- and channel-forming 2,4,6-triarylpyrylium crystal structures. Three conserved local interactions were identified, including C-H···X- interactions, the rhombic binding pocket, and four-ring antiparallel dimerization. Development of this library of interaction motifs rationalizes the packing arrangement of the co-crystal and contributes to the informed design of anion exchange materials. [ABSTRACT FROM AUTHOR]

Ring contraction of 2,4,6-triarylpyrylium perchlorates by use of sodium nitrite mediated by ionic liquid has been used as a new, direct, and environmentally benign method for synthesis of bioactive 2-aroylfuran and novel 3,5-diaroyl-4-arylisoxazole derivatives in excellent yields. The versatility of the approach enables rapid and simple access to these pharmaceutically important compounds. The products were readily isolated from the reaction mixture by simple filtration. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Systematically varied pyrylium and thiopyrylium photo-oxidants have been evaluated in the metal-free ring-opening-metathesis polymerization (MF-ROMP) of norbornene. Across the series, we observed higher conversion into polynorbornene from thiopyrylium species in comparison with pyrylium salts that were otherwise similarly functionalized. Additionally, more electron-rich photo-oxidants (i.e., weaker oxidants) correlated with higher conversions. [ABSTRACT FROM AUTHOR]

Eight anthocyanidins, seven anthocyanins and two synthesized 4′-hydroxy flavyliums were examined as hydrogen donors to DPPH, ABTS and hydroxyl radicals, and as electron donors in the FRAP assay. Most compounds gave better activities than trolox and catechol. A structure–activity relationship (SAR) study showed that, in the absence of the 3-OH group, radicals of the 4, 5 or 7-OH groups can only be stabilized by resonance through pyrylium oxygen, while 3-OH group improved hydrogen atom donation because of the stabilization by anthocyanidin semiquinone-like resonance. Electron donation was also enhanced by the 3-OH group. Both anthocyanidins and their respective anthocyanins showed similar trends and close activities. Different types of sugar unit bonded to the 3-OH group or counter ion had minor effect on activities. The catechol structure improved both hydrogen and electron donation. Compounds lacking the catechol structure had a decreasing order of H-atom and electron donation (Mv > Pn > Pg > Ap > 4′-OH-flavylium) consistent with the decreasing number of their hydroxyl and/or methoxy groups. [ABSTRACT FROM AUTHOR]

An expedient synthesis of amino-(nor)dihydroxanthene-based fluorophores is reported, proceeding in two steps from commercially available salicylic aldehydes. The synthesis relies on the one-pot construction of the (nor)dihydroxanthene scaffolds through an oxa-Michael/retro-Michael/vinylogous aldol/dehydration cascade sequence. Further extension of the π-conjugated systems through a condensation reaction with a 2,4,6-trisubstituted pyrylium salt led to a novel class of near-infrared (NIR) fluorescent dyes with absorption/emission maxima in polar media in the ranges of 705–778 and 785–828 nm, respectively. [ABSTRACT FROM AUTHOR]

Unsymmetrical polymethine dyes have been synthesized from 6- tert-butyl-4-methylthioflavylium perchlorates and nitrogen-containing heterocyclic aldehydes derived from julolidine and polyfluorinated triphenyl-4,5-dihydro-1 H-pyrazoles. Spectral characteristics of the obtained compounds have been studied. [ABSTRACT FROM AUTHOR]

We synthesized a pyrylium–coumarin dyad (1) and used it for colorimetric detection of cyanide anions (CN−) in aqueous media. The receptor itself exhibits a long-wavelength absorption band at 643 nm due to the strong intramolecular charge transfer (ICT) from the diethylaminocoumarin to the pyrylium moiety. Selective nucleophilic addition of CN−to the pyrylium ring triggers the ring cleavage rapidly (within 8 min). This suppresses the ICT and decreases the intensity of the 643 nm band, along with an appearance of a new shorter-wavelength band at 472 nm assigned to the π,π* transition of the diethylaminocoumarin moiety. This drastic absorption change (643 nm → 472 nm) facilitates ratiometric detection of CN−based on the intensities of these two absorption bands in the visible region and successfully detects CN−as low as 8 μM. [ABSTRACT FROM AUTHOR]

Bis-acyl derivatives of diphenyl sulfide and diphenyl ether were synthesized by successive Friedel-Crafts acylations with 2-bromo-2-methylpropanoyl bromide and acetyl chloride. The subsequent reaction with sodium p-toluenesulfinate afforded the corresponding sulfones, and condensation of the latter with benzaldehyde in acetic acid in the presence of perchloric acid gave pyrylium salts with a β-ketosulfonyl fragment in the side chain. [ABSTRACT FROM AUTHOR]

A high-performance liquid chromatography method based on pre-column derivatization with the pyrylium salts (4-[p-(N,N-dimethylamino)phenyl]-2,6-diphenylpyrylium perchlorate (LN1) and 2,4,6-triphenylpyrylium tetrafluoroborate (L1)) has been developed for the determination of sulfide. After the reaction of sulfide ions with LN1 or L1 aiming at the formation of the corresponding thiopyrylium derivatives LN3 or L3, they were separated on a C18 column using phosphate buffer and acetonitrile as eluent, and afterwards detected with a UV/vis detector. By using the described method, sulfide ions can be determined in the range of 5.12–486.4 μg . L −1 or 1.024–20.48 μg . L −1 by means of L1 or LN1, respectively. In our experiments, the relative standard deviation was not higher than 2% and the recovery coefficient was in the range of 88–102%. The proposed method was applied to the determination of sulfide in spring water samples from Busko Zdrój and Uniejów health resorts located in Poland. [ABSTRACT FROM AUTHOR]