Über die Wirkung von Auxochromen in Flavyliumsalzen,I. 7-Hydroxy-flavyliumsalze

7-Hydroxy-flavylium salts absorb at longer wave lengths than the corresponding flavylium salts, yet auxochromes in 4′-position have a less bathochromic effect in the 7-hydroxy-flavylium series than in the flavylium series. As a result the absorption maxima converge. 4′-Dimethylamino derivatives show a convergence of 22 nm.     

Über die Wirkung von Auxochromen in Flavyliumsalzen,II. 5,6-Benzo-flavyliumsalze

Analogously to the 7-hydroxyflavyliumion the 5,6-benzoflavyliumion affects auxochromes in 4′-position not as strongly as the flavylium ion. In the flavylium series the dimethyl-amino group e.g. causes a bathochromic effect of 137 nm; in the 5,6-benzoflavylium series however the bathochromic effect is only 109 nm. The absorption maxima of both series converge; in the case of the dimethylamino group the convergence amounts to 28 nm.     

Preparation of bis-pyrylium salts

Six methods are described for the preparation of bis-pyrylium salts: (1) treatment of 4,4′-bi-2-flavene or 4-(4H-flav-2-en-4-yl)flavylium perchlorate with triphenylmethyl perehlorate; (2) reaction of an aromatic o-hydroxyaldehyde and 1,4-deacetylbenzene under acidic conditions; (3) reaction of o-hydroxyacetophenone, 1,4-diacetylbenzene, perchloric acid and acetic acid; (4) reaction of a 2- or 4-methylpyrylium salt with 2- or 4-pyrone in the presence of phosphorus oxychloride; (5) oxidation of a 1,2-ethanediylidenebis-flavene or -thiaflavene, a bis-flavenylidene or -thiaflavenylidene, and a bis-pyranylidene or -thiapyranylidene by means of cupric perchlorate; and (6) reaction of 4-methylflavylium and -thiaflavylium perchlorate with bromine in acetic acid.     

Über den Verteilungssatz der Auxochrome bei Azokörpern,I. Di- und Tetramethoxy-xobenzole

The validity of the rule of repartition of the auxochromes is examined for some symmetric tetramethoxy-azobenzenes, dimethoxy-azobenzenes, and dimethoxy-4′-nitro-azobenzenes whose methoxy groups are in 2,4-, 3,4- and 2,5-position. The rule is confirmed with 2,4-and 2,5-derivatives. The long wave lengths absorption maxima of 3,4,3′,4′-tetramethoxy-azobenzene and of 3,4-dimethoxy-4′-nitro-azobenzene are situated at shorter wave lengths than expected.     

Über den Verteilungssatz der Auxochrome bei Azokörpern,II Dihydroxy-azobenzole

The validity of the rule of repartition of the auxochromes is examined for dihydroxy-azo and dihydroxy-4′-nitro-azo compounds with hydroxy groups in 2,4-, 3,4- and 2,5-position. In conformity with the rule the absorption maximum of the 2, 5-dihydroxy-azobenzene is situated at a considerably longer wave length than the maximum of 2,4-dihydroxy-azobenzene. The 3, 4-isomer with its absorption maximum at a relatively short wave-length seems to contradict the rule. On the other hand all alkali salts of both series conform to the rule of repartition in an impressive way.     

Reaction of some pyrylium salts with hydrazine

2,6-Diphenyl- and 2,6-di-tert-butylpyrylium salts react with excess hydrazine to give 1,2-diazeplne derivatives. Under the same conditions, 4-(1-methyl-3-indolyl)flavylium perchlorate forms 3-phenyl-5-(1-methyl-3-lndolyl)pyrazole.Translated from Khimiya Geterotsiklichesikikh Soedinenii, No. 1, pp. 45–48, January, 1973.     

Reaction of methyl-substituted pyrylium salts with tertiary amines

2,4,6-Trimethylpyrylium perchlorate reacts with heterocyclic compounds containing apyridine nitrogen atom and having basicities higher than 9 pK_a units (in acetonitrile) through a step involving the formation of a methylenepyran. 4-Methyl-2,6-diphenyl- and 2-methyl-4,6-diphenylpyrylium perchlorates react with benzimidazole to give 1,2-ethanediylidenebispyrans. Methyl-substituted pyrylium salts react with 2,6-diphenylpyrylium and flavylium perchlorates in the presence of benzimidazole to give methylidynecyanines and with acetic anhydride to give trimethylidynecyanines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1484–1489, November, 1976.     

Formation of a leuco Spirolactone from 4‐(2‐Carboxyphenyl)‐7‐diethylamino‐4′‐dimethylamino‐1‐benzopyrylium: Design of a Phase‐Change Thermochromic System Based on a Flavylium Dye

A phase‐change thermochromic system was designed through the reversible transformation of the 4‐substituted flavylium dye 4‐(2‐carboxyphenyl)‐7‐diethylamino‐4′‐dimethylamino‐1‐benzopyrylium into its leuco form, in the presence of a developer (ethyldiisopropylamine) and a suitable solvent (e.g., acetonitrile, n‐pentadecanonitrile). The leuco form of the flavylium‐based dye is a spirolactone species whose ring opens at low temperature (below the solvent melting point) to form the blue flavylium cation. Decarboxylation of the lactone to give 4‐phenyl‐7‐diethylamino‐4′‐dimethylamino‐1‐benzopyrylium was observed upon irradiation of the system with UV light, erasing the thermochromic effect.     

Thiapyrylocyanines

The reaction of thiaflavones with methylmagnesium iodide has yielded 4-methylthiaflavylium salts, from which a number of symmetrical and unsymmetrical polymethine dyes have been obtained. The thiaflavylocyanines have considerably deeper colors than the flavylocyanines. The thiaflavylium styryl dyes, like the flavylium analogs, have negative deviations. It follows from the results on the deviations that in the polymethine dyes the thiaflavylium nucleus behaves as less basic than the flavylium nucleus.     

Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals

Thermotropic ionic liquid crystals based on the flavylium scaffold have been synthesized and studied for their structure-properties relationship for the first time. The mesogens were probed by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Low numbers of alkoxy side chains resulted in smectic (SmA) and lamello-columnar (Lam_Col) phases, whereas higher substituted flavylium salts showed Col_ro as well as ordered and disordered columnar (Col_ho, Col_hd) mesophases. Mesophase width ranged from 13 K to 220 K, giving access to room temperature liquid crystals. The optical properties of the synthesized compounds were probed towards absorption and emission properties. Strong absorption with maxima between 444 and 507 nm was observed, and some chromophores were highly emissive with quantum yields up to 99 %. Ultimately, mesogenic and dye properties were examined by temperature-dependent emissive experiments in the solid state.     

Ring transformations of heterocyclic compounds. XVI. Spiro[cyclohexadiene-dihydroacridines]. A novel class of spirodihydroacridines by ring transformation of pyrylium salts with 9-methylacridine and its quaternary salts

2,4,6-Triarylpyrylium salts 1 react with the in situ generated anhydrobase of 9,10-dimethylacridinium methosulfate ( 2a ) in the presence of anhydrous sodium acetate in ethanol by a 2,5-[C₄+C₂] pyrylium ring transformation to give the hitherto unknown 6-aroyl-3,5-diaryl-10′-methylspiro[cyclohexa-2,4-diene-1,9′-9′,10′-dihydro-acridines] 3 . When the pyrylium perchlorate 1a is treated under the same conditions with the N-ethyl, N-allyl or N-benzyl substituted acridinium salts 2b-d a dealkylation of these salts occurs and the N-unsubstituted spiro[cyclohexadiene-dihydroacridine] 4a is formed. The same compounds 4 can also be obtained by transformation of the pyrylium salts 1 with 9-methylacridine ( 7 ) and triefhylamine/acetic acid in ethanol. Structure elucidation is performed by an X-ray crystal structure determination of the spiro[cyclohexadiene-dihydroacridine] 3a . Spectroscopic data of the transformation products and their mode of formation are discussed.     

Pyrylium salts in the synthesis of redoxites

Redoxites poly(2,6-diphenyl-4-vinylpyran), poly(2,6-diphenyl-4-vinylpyrylium perchlorate), poly-(2,6-diphenyl-4-vinylpyridine) and poly(2,2′,6,6′-tetraphenyl-γ,γ′-dipyridine) were obtained based on pyrylium salts. Poly(2,2′,6,6′-tetraphenyl-γ,γ′-dipyridine) was transformed into the polyene to improve its film-forming and conducting properties. Electrochemical properties of polyviologen and conductive properties of the obtained polymers were studied.     

Promoting photochromism on flavylium derived 2-hydroxychalcones in aqueous solutions by addition of CTAB micelles

A strategy to obtain photochromism from the network of chemical reactions originated by flavylium compounds in solution is described. This strategy is particularly useful for flavylium salts bearing amino groups which give rise to a variety of beautiful colors but lack photochemistry in water. The trans-chalcone of 7-(N,N-diethylamino)-4'-hydroxyflavylium interacts strongly with CTAB micelles defining a yellow dark state. Upon irradiation, the system switches to a pink-red state emerging from the flavylium cation that is formed inside the micelle and ejected to the bulk aqueous phase. The photochemical product reverts back to the trans-chalcone adduct with the micelle in the dark. The thermodynamics as well as the kinetics of the photochromic system were studied in detail. The best color contrast is obtained at pH = 4.25 with Phi = 0.001 and a recovery lifetime of approximately 3 h. This photochromic system works with no need of changing the pH, which constitutes an important improvement over previously described systems dependent on pH jumps.     

Unidirectional switching between two flavylium reaction networks by the action of alternate stimuli of acid and base

The introduction of an ester group in the flavylium core allowed the reversible conversion between two different flavylium compounds each one exhibiting its own reaction network. An unidirectional switching cycle between 7-diethylamino-2-(4-(methoxycarbonyl)phenyl)-1-benzopyrylium and 2-(4-carboxyphenyl)-7-diethylamino-1-benzopyrylium was achieved by means of alternate acid and base stimuli. Addition of base to a methanolic solution of the ester derivative gives rise to the trans-chalcone of the parent carboxylic acid, which upon acidification of the solution forms the respective flavylium cation. This species esterifies under very acidic conditions to restore the original methyl ester derivative. The chemical reaction networks of both compounds were fully characterized from their thermodynamic and kinetic aspects, by a series of pH jumps followed by UV-vis absorption and emission spectroscopy, stopped flow and (1)H NMR. The crystal structure of the trans-chalcone of the ester derivative was unveiled showing a supramolecular structure involving hydrogen bonding.     

Anthocyanidins and related compounds—VII Reactions of flavylium salts with 5,5-dimethyl-1,3-cyclohexanedione at pH 5·8

Phenolic flavylium salts, substituted and unsubstituted at position 3, condense with 5,5-dimethyl-1,3-cyclohexanedione in aqueous methanolic solutions at pH 5·8 to form novel cyclic flavan derivatives of types Xa and XIa.     

Synthesis and absorption spectra of some 2,6-disubstituted 4-(4-dimethylaminophenyl)thiopyrylium perchlorates

The syntheses of 4-(4-dimethylaminophenyl)thiopyrylium perchlorate and the 2,6-dimethyl derivative are described, and the absorption spectra of these compounds and the 2,6-diphenyl derivative are compared with the corresponding pyrylium salts.     

Some reactions of 4H-pyrylium salts with tributylphosphine and with tertiary amines

The phosphonium salt from tributylphosphine and 2,6-di(4-methoxyphenyl)pyrylium perchlorate (3) reacted with diisopropylethylamine in acetonitrile to give 2,2′,6,6′-tetra(4-methoxyphenyl)-Δ^4.4′-bi-4H-pyran in quantitative yield. The reaction of 3 and other 4H-pyrylium salts with tertiary amines gave 4H-pyrans.     

3,3′-bis(dipyrrolylmethenes) as new chelating ligands: Synthesis and spectral properties

Hydrobromides of three new alkyl-substituted tetrapyrrole ligands with an open chain, in which the dipyrrolylmethene fragments are linked by a CH₂-spacer at the 3,3′-pyrrole carbon atoms, were synthesized and studied by IR, ¹H NMR, and electronic absorption spectroscopy. As compared to the 2,2′ isomers (alkyl derivatives of biladiene-a,c) and monomers (2,2′-, 2,3′-, and 3,3′-dipyrrolylmethenes, the effect of structural factors is manifested in a considerable (up to 19–31 nm) bathochromic shift of the strong band in the electronic spectrum, an increase in the N-H stretching vibration frequency in the IR spectra (by more than 30 cm^?1), and a decrease in the stability of 3,3′-bis(dipyrrolylmethene) salts. The solvent effect is manifested in small changes in the quantitative characteristics of the electronic absorption spectra of 3,3′-tetrapyrrole hydrobromides in C₆H₆, CCl₄, CH₂Cl₂, CHCl₃, and alcohols. In DMF, DMSO, and C₅H₅N, the salts undergo solvolytic dissociation to the free ligands and HBr, which accelerates in dilute solutions (<10^?4 M) and with an increase in the electron-donor power of the solvent. The auxochromic effects of protons in the electronic absorption spectra of the salts, compared to ligands, were estimated quantitatively.     

Reactions of 4-ethoxyflavylium, 4-ethoxychromylium,and 4-ethoxyfurochromylium salts with several amines

The reactions of 4-ethoxyflavylium, 4-ethoxychromylium, and 4-ethoxyfurochromylium salts in acidic media with several acids were investigated. In the reaction with hydrazine the furochromylium salt forms pyrazole, whereas both α,β-substituted benzopyrylium salts are converted to azines. The reaction of hydroxylamine with the flavylium salt gives a flavone oxime, whereas the reaction with the furochromylium salt gives an isoxazolylbenzofuranol.     

THE INFLUENCE OF FLAVONOID SULFONATES ON THE FLUORESCENCE AND PHOTOCHEMISTRY OF FLAVYLIUM CATIONS

Abstract— The effects of flavone sulfonic acid 9 andquercetin–5'-sulfonic acid 10 on the luminescence spectra of eight flavylium salts have been determined. The non-hydroxylated flavone 9 was found to enhance the luminescence of those flavylium salts, while the polyhydroxyflavonol 10 was shown to exert the opposite effect. These findings are rationalized in conjunction with prior observations on the enhancement and inhibition of the photodecomposition of anthocyanins exerted by 9 and 10 , respectively.