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The spectral and fluorescent properties of cross-conjugated bichromophoric ω,ω′-aminopolyenes containing the pyran or dihydropyridine cycle with acceptor groups of different structures have been studied. According to the two-dimensional 1H NMR spectroscopy (NOESY and ROESY) data obtained earlier, chromophores are arranged at an acute or obtuse angle in compounds with the pyran or the dihydropyridine moiety, respectively, thereby leading to significant differences in the absorption spectra of these compounds. The absorption spectra have been considered on the basis of the theory of interaction of chromophores. Since the long-wavelength bands of the absorption spectra of the compounds with the dihydropyridine cycle are broad and poorly resolved, we used decomposition of the absorption spectra of these compounds into Gaussian components. The angles between the chromophores, estimated from the ratio of the intensities of the absorption bands, were found to comply with the NMR data. Fluorescence quantum yields of the compounds studied have been also determined. In the case of the dyes with carbonyl, dinitrile, or indandione acceptors, the fluorescence quantum yields were found to be significantly higher for the compounds with the pyran rather than the dihydropyridine cycle.

New cross-conjugated ω,ω′-dimethylaminopolyenes containing the central pyrane or N-methyldihydropyridine fragment were synthesized. In new compounds, the interaction of the aminopolyene chromophores occurs through the dicyanomethylidene, 1-cyano-1-(4-nitrophenyl)methylidene, or 1,3-dioxoindan-2-ylidene groups in position 4 of the heterocycle. The conformation of the synthesized compounds was determined by 2D 1H NMR spectroscopy (NOESY and ROESY): the chromophores are arranged at an acute or obtuse angle in the structures with the pyrane or dihydropyridine fragment, respectively. The conformational differences in polyenes result in a drastic change in their spectral properties: for the dyes with an acute angles between the chromophores, the long-wavelength absorption band is less intense, as a rule, than the shorter-wavelength band, while the situation is opposite for the compounds with an obtuse angle. The absorption spectra of the synthesized compounds with dinitrile and other acceptor groups lie in a longer-wavelength region than the absorption spectra of the corresponding compounds with carbonyl acceptor groups. The central bridging substituent NMe decreases the energy of interaction of the chromophores.

The spectral, fluorescent, and photochemical properties of new merocyanines containing nitrile groups as acceptors have been studied. Positive solvatochromism is observed for most of these compounds; however, for the dye containing three nitrile groups as acceptors—polyenic aminotrinitrile—negative solvatochromism is observed: the absorption spectrum is shifted to shorter wavelengths with increasing the solvent polarity. In all solvents used, the fluorescence and fluorescence excitation spectra of the merocyanines almost do not depend on the excitation and fluorescence registration wavelengths, respectively. Using the flash photolysis method, the formation of photoisomers of the merocyanines has been detected and the kinetics of their decay in solvents of different polarity has been studied. Backward (dark) isomerization of the photoisomers has been shown to take place more slowly in nonpolar solvents.

Reactions of N-acetyl- and N-benzyl-4-piperidones with aminal of β-dimethylaminoac-rolein yielded ketocyanines bearing piperidine cycle. Reaction of 3-dimethylamino-1,1,3-trimethoxypropane with 1-acetylpiperidin-4-ylidenemalononitrile in the presence of ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4), resulted in cross-conjugated ω,ω’-dimethylamino dinitrile. Protonation of ketocyanines bearing N-acetyl- and N-benzyl-piperidine cycles with Et2O·HBF4 (1 equiv.) furnished piperidinium salts, while protonation of the latter with Et2O·HBF4 (2 equiv.) afforded doubly charged 4-hydroxypolymethine salts. Unlike protonation, reaction of 3,5-bis(3-dimethylaminoprop-2-enylidene)-1-acetylpiperidin-4-one with Me2SO4 involved only the oxygen atom and led to a singly charged 4-methoxypolymethine salt. Methylation of 3,5-bis(3-dimethylaminoprop-2-enylidene)-1-benzylpiperidin-4-one with Me2SO4 (1 equiv.) involved cyclic nitrogen atom and resulted in piperidinium salt; heating of the latter with the excess of Me2SO4 afforded doubly charged bis-methoxysulfonate. Starting from 4-methoxytetrahydropyridinium salts, meso-methoxythiapentacarbocyanine dyes were synthesized.

Protonation or alkylation of 3,5-bis(3-dimethylaminoprop-2-enylidene)-1-methylpiperi-din-4-one with Et2O∙HBF4, Et3O+BF4-, Me2SO4, or Et2SO4 (1 equiv.) involves the endocy-clic N atom, yielding the corresponding piperidinium salts. With 2 equivalents of the above reagents, the reactions occur at two reactive sites (the N and O atoms) to give doubly charged 4-hydroxy or 4-alkoxy polymethine salts. Protonation and alkylation of ethyl 3,5-bis(3-dimethyl-aminoprop-2-enylidene)-4-oxopiperidine-1-carboxylate involve only the O atom, affording the corresponding singly charged 4-hydroxy and 4-alkoxy polymethine salts. The latter were used to obtain previously unknown meso-alkoxythiapentacarbocyanine dyes containing the 1-ethoxycarbonyl-1,2,3,6-tetrahydropyridine fragment in the polymethine chain.

The spectral and fluorescent properties of a number of ωω′-bis(aminopolyenyl)ketones (ketocyanines) and ωω′-bis(3-dimethylaminopropen-2-yliden)-alkylidenmalononitriles (dinitriles), being analogues of usual ketocyanines, but containing the dicyanomethylene fragment instead of the carbonyl group, were studied. Specific and nonspecific solvation of dinitriles and corresponding ketocyanines was studied on the basis of the solvatochromic shifts of the absorption spectra. The photophysical data obtained for the different molecular structures were correlated with different empirical parameters, which characterize solvation by organic solvents: the Dimroth-Reichardt ET(30) parameter of the solvating power, the acceptor number AN, the donor number DN, and the constant π* characterizing the solvent polarity and polarizability. A linear dependence of the maximums in the absorption spectra on the acceptor number AN, which characterizes specific solvation, was found for the ketocyanines under study. This indicates that the electrophilic solvation plays a key role in ketocyanine solutions. For dinitriles, the linear dependence of the maximums of the absorption spectra was obtained as f(π*, AN, DN). In the latter case, along with the electrophilic solvation, there is a substantial contribution of nonspecific and nucleophilic solvation.

N-Substituted 4-piperidones react with β-dimethylaminoacrolein aminals to give keto-cyanines containing a piperidine ring. A reaction of 3-dimethylamino-1, 1,3-trimethoxypropane with 1-ethoxycarbonylpiperidin-4-ylidenemalononitrile produces a cross-conjugated ω,ω′-bis-(dimethylamino) dinitrile. Its yield is doubled when ionic liquids are used. The spectroscopic properties of the compounds obtained are highly sensitive to the structure: replacement of the C=O group in ketocyanines by the C=C(CN)2 group results in a considerable bathochromic shift of the absorption spectra, while replacement of the central bridging fragment (CH2)3 by (CH2)4 results in a hypsochromic shift. All the compounds obtained exhibit positive solvatochromism.

A reaction of 2,2-disubstituted 1,1-dicyanoethenes with β-dimethylaminoacrolein aminal and 3-dimethylamino-1,1,3-trimethoxypropane leads to substituted 6,6-dicyano-1-dimethyl-aminohexatrienes and an organic salt containing 1,1,9,9-tetracyano-2,8-diphenylnona-2,4,6,8-tetraenide as the anion and (dimethylaminopropenylidene)dimethylammonium as the cation, on the basis of which new cation-anionic polymethine dyes were obtained.

Reactions of 3-(dicyanomethylidene)indan-1-one and 1,3-bis(dicyanomethylidene)indane with β-dimethylaminoacrolein aminal, 3-dimethylamino-1,1,3-trimethoxypropane, DMF acetal, and ethyl orthoformate were studied. The reaction of 3-(dicyanomethylidene)indan-1-one with 3-dimethylamino-1,1,3-trimethoxypropane gave the 1,3-bis(1-dicyanomethylidene-3-oxoindane)trimethineoxanine salt in high yield, which was used to obtain a number of novel cation-anionic polymethine dyes.

The electronic transitions in molecules of the ketocyanine dyes (polyenic ω,ω′-bisamino ketones) were calculated by quantum chemical methods. Satisfactory agreement was obtained between the experimental bands of the S-S absorption spectra and calculated electronic transitions for the ketocyanine with the central pyranone moiety and the corresponding salt assuming an acute angle between the chromophores and for the ketocyanine with the central pyridone moiety assuming an obtuse angle between the chromophores. Such molecular conformations were confirmed by the gNOESY 1H NMR data for these dyes. The difference in the conformations of the dyes with the pyranone and pyridone moieties is due, most likely, to steric hindrance created by the central methyl groups in the molecules of the latter. The salts corresponding to these dyes have similar conformational differences.

The spectral and fluorescent properties of (bis-θ,θ′-dimethylaminopolyenyl)diketones were studied. It was found that the presence of two carbonyl groups in the diketone structure leads to a bathochromic shift of the absorption spectrum of the dye with respect to that of the corresponding compound with one carbonyl group. The shift is presumably due to a greater extent of charge transfer from the terminal amino groups to the central carbonyl groups than in the corresponding ketocyanine with one carbonyl group. The 13C NMR spectra of these dyes also indicate that the electronic structure of the diketones is closer to the polymethine state with equalized bonds than in the case of corresponding usual ketocyanines. The diketones are readily protonated by trace acids. The prototropic equilibrium constants measured for the diketones turned out to be close to those for the dye with one carbonyl group.

Bis-and tetrakis(ω-dimethylamino)-substituted cross-conjugated polyene α-diketones, containing two thiophene rings, were synthesized from α-diketones of the thiophene series and β-dimethylaminoacrolein aminals and also 2-aza-3-dimethylaminoacrolein acetal.

The protonation and alkylation of cross-conjugated ketones containing a terminal N-methylpyrrole ring takes place at the oxygen atom. Protonation is accompanied by a strong bathochromic shift of the absorption maximum in the electron spectrum, while alkylation leads to ethoxypolymethine salts. The possibility of using these salts for the synthesis of ethoxycyanine dyes was studied.

The reactions of substituted 4H-pyrones and N-methyl-2,6-dimethylpyridone with dimethylformamide acetal and aminal acetals of conjugated ω-dimethylaminoaldehydes were studied. Cross-conjugated ketones and meso-ethoxy(dialkylamino)tridecamethine salts containing the pyran or pyridone fragment were synthesized and their spectroscopic properties were investigated. The replacement of the bridging O atom by the NMe group precludes an interaction between chromophores in cross-conjugated ketone and the related tridecamethine salt. In addition, the insertion of a meso-amino substituent into the polymethine chain of the salts containing the central pyrylium fragment leads to a sharp weakening of the chromophore interaction. In spite of the dramatic differences in the UV spectra of ketocyanines containing the bridging O or NMe fragments, these dyes have similar 13C NMR spectra.

Methods for the synthesis of various types of polyfunctional conjugated polyenes based on aminals of unsaturated ω-amino aldehydes are surveyed. The influence of the interaction of chromophores on the photophysical properties of polyene bis(amino)-substituted ketones and polymethine salts based on them as well as on the properties of absorption and fluorescence spectra of the cation-anionic polymethine dyes are considered.

Fluorescent properties of some cross-conjugate ketones were studied at 4.2, 77, and 300 K. Anomalies were observed in the fluorescence and fluorescence-excitation spectra of one of the studied compounds; these anomalies consisted in a pronounced upset of mirror symmetry of the spectra and a large Stokes shift. The experimental spectra and the spectra calculated theoretically using the theory of two-well adiabatic potentials were subjected to a comparative analysis.

The published data on the synthesis of β-enamino ketones, δ-amino dienones and conjugated ω-amino polyenones of diverse structures are generalised. The bibliography includes 129 references.

Spectral and fluorescent properties of ketocyanine dyes (polyenic bis-ω,ω′-aminoketones) and cation-anionic polymethine dyes of various structures were studied. The symmetric ketocyanines were shown to have a long-wavelength absorption band bathochromically shifted in comparison with that of the asymmetric ketocyanines with the same total length of the polyenic chain. The nonlinear ketocyanines exhibit the additional short-wavelength band in their absorption spectra, which can be more intense than the longwavelength band. The absorption spectra of ion pairs of cation-anionic dyes with overlapping cation and anion bands contain a new intense short-wavelength band inactive in fluorescence excitation. These spectral peculiarities are explained on the basis of chromophore interaction model. It has also been shown that theT1levels of ketocyanine chromophores do not essentially interact with each other in a ketocyanine molecule in nonpolar solvents; in polar solvents this interaction becomes appreciable due to lowering the potential barrier for conjugation.

The researches of the author and her colleagues on the synthesis of α α-dicarbonyl-containing dienes with various structures and study of their valence isomerization to 2H-pyrans1H by an13C NMR, UV, and IR spectroscopy and flash photolysis are reviewed.

The reactions of β-dimethylaminoacrolein aminals with 2,6-dimethyl-γ-pyrone lead to 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones, whose alkylation affords ethoxytridecamethine salts. The spectral and fluorescence properties of the synthesized compounds were studied. Their absorption spectra are unusual; along with the long-wavelength band in the visible spectral region, they contain a much more intense short-wavelength band in the near UV region. This pattern of the absorption spectra is explained in terms of the model of chromophore interaction, assuming an acute angle between the chromophore “halves” of the polyene chain of the dye molecule. The central pyran ring in the ethoxytridecamethine salts can hamper conjugation in the polymethine chain. Thermochromism of 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones (the long-wavelength shift of the absorption spectra on cooling of the solutions) is observed; only the long-wavelength absorption band undergoes a pronounced thermochromic shift. The introduction of methyl or phenyl substituents into the polyene chains of substituted 4H-pyranones decreases the fluorescence quantum yield.

The spectral and fluorescent properties of a number of cross-conjugated ketones with one or two terminalN-methylpyrrole residues and those of polyene bis-ω, ω′-dimethylamino ketones with methyl substituents in the polyene chain and of some related compounds were studied. The photophysical properties of cross-conjugated ketones with terminalN-methylpyrrole residues are similar to those of the corresponding polyene bis-ω, ω′-dimethylamino ketones studied in detail previously. In both series of compounds, the absorption and fluorescence spectra undergo a bathochromic shift following an increase in the length of the polyene chains or introduction of α,α′-trimethylene or α,α′-dimethylene bridges into these chains; the same trend is observed on passing from less polar solvents to more polar solvents (positive solvatochromism). Thermochromism (long-wavelength shift of the absorption spectra upon cooling the solutions) is observed in both series of compounds. The introduction of methyl substituents into the polyene chains of bis-ω,ω′-dimethylamino ketones results in a decrease in the fluorescence quantum yield.

Depending on the reaction conditions, dimethylaminomethylenemalonaldehyde aminal acetal reacts with malonodinitrile or alkyl cyanoacetates to give various neutral or ionic cross-conjugated polynitriles. Cation-anionic cyanine dyes were obtained from tri- and tetracyanopolymethine salts. The conformation and geometric parameters of the tetramethyl 3-dimethylaminomethylenepenta-1,4-diene-1,1,5,5-tetracarboxylate molecule were established by X-ray diffraction analysis.

The reaction of β-hetarylacrolein and β-hetaryl-α-methylacroleins with esters of acetoacetic and malonic acids was studied. The structures of the products obtained were established using1H and13C NMR and UV spectroscopy. (E) and (Z) isomers of α,α-dicarbonylalkadienes, their mixtures with the corresponding 2H-pyrans or exclusively 2H-pyrans are formed depending on the substitution in the starting aldehyde and the ester used. 6-Methyl- and 3,6-dimethyl-5-carbalkoxy-2-(2-pyridyl)pyrans are converted upon heating to substituted 2-(pyrilidene)pyrans.

Condensation of the bis-N,O-acetal of amethylarrtinomethylenerrzalonaldehyde with ketones, β-dimethylaminovinylketones, and δ-dimethylaminodienones is accompanied by an unusual intramolecular cyclization to give cross conjugated cyclic or acylic ketones containing an N-methyl pyrrole ring in the β- or β- andβ'-positions. This is a novel route to substituted pyrroles. Treatment of the bis-N,O-acetal of dimethylaminomethylenemalonaldehyde with 2-(3'-dimethylaminopropen-2'-ylidene)cyclopentanone gave a polyenyl tris-dimethylaminodiketone.

β-Cyclohexylacrolein, β-cyclohexylmethacrolein, or α-cycloalkylidenalkanals were condensed with methyl acetoacetate or dimethyl malonate to give the δ-cyclohexyl- and δ,δ-alkylene-substituted α,α-dicarbonyl-containing α,β∶γ,δ-dienes. The structures of the reaction products were studied using1H NMR,13C NMR, and UV spectroscopy. The diene keto esters bearing no substituents at the γ-position were shown to be in fact three-component equilibrium mixtures comprised ofE- andZ-isomers of the diene (at the α,β bond) and a corresponding 2H-pyran. On the other hand, for keto esters with a Me group at the γ-position the equilibrium is shifted entirely to the 2H-pyrans. In contrast with the keto esters, dienic diesters exist only in the open form.

Photoinduced electron transfer in ion pairs of cation-anion polymethine dyes was studied by flash photolysis. The formation of radicals, which are the products of photoinduced transfer of an electron from an anion to a cation in the ion pairs, was observed during photoexcitation of a number of cation-anion dyes in nonpolar and some weakly polar solvents (in particular, in toluene and chloroform). Photoinduced electron transfer is also observed during triplet sensitization of ion pairs of the cation-anion dyes. The redox potentials of the cations and anions constituting the dyes were measured; the radical yields were compared with the free energies of photoinduced electron transfer. Photoinduced electron transfer in the systems under study was compared with similar process in cyanineborate ion pairs.

The reactions of aminals of conjugated ω-dimethylaminoaldehydes with various derivatives of 4-methyl- or 3-acetyl coumarins produce ω-dimethylaminopolyenones containing coumarin fragments. Unlike the starting coumarins, these polyenones practically do not fluoresce. Dialkyl-substituted coumarins with hydroxyl groups in positions 5 or 7 react with β-dimethylaminoacrolein aminal to give salts consisting of 1 mole of doubly charged dimethylaminopropenylidenedimethylammonium cations and 2 moles of phenoxide ions (derived from the starting coumarins). The structure and the properties of the salts in solutions have been studied by absorption and fluorescence spectroscopy.

The absorption, fluorescence, and excitation spectra of two cation-anionic dyes with simple structures, which have the identical anions and variable cations, were studied in weakly polar and nonpolar solvents as well as in binary mixtures of solvents with different polarity. Under these conditions heterogeneous fluorescent aggregates were found at 20 °C. The structure of the cation has a significant influence on the formation and properties of the aggregates of cation-anionic polymethine dyes.

Reactions of aminals of conjugated ω-dimethylaminoaldehydes with Meldrum's acid,N,N′-(o-phenylene)malonamides, and 2,3-dihydrophenalene-1,3-dione afford δ-dimethylaminodienones, substituted 2-dimethylamino-2H-pyrans, or oxanine salts. Cation-anionic polymethine dyes have been obtained from the latter.

The condensation of aminals of β-dimethylaminoacrolein and 5-dimethylaminopenta-2,4-dienal with cyclic and acyclic 1,2-, 1,3-, 1,4-, 1,5-, and 1,6-diketones was studied. A series of previously unknown bis(ω,ω′-dimethylaminopolyenyl)diketones was synthesized; their structures were established by means of1H and13C NMR spectroscopies. The electron absorption spectra were employed to study the mutual influence of ω-aminopolyene chromophores separated by two C=O groups.

The effect of solvent polarity and ion pair formation oncis-trans-isomerization of cationic-anionic polymethine dyes and of related simple cationic and anionic dyes is studied by flash photolysis. The change in the rate constant for reversecis-trans- isomerization of photoisomers due to the interaction of a cation with an anion in an ion pair is observed in nonpolar solvents. A drop in the yield of the photoisomers to zero is observed for a number of cationic-anionic dyes in weakly polar and nonpolar solvents which is possibly due to steric hindrances in the photoisomerization process in ion pairs.

Spectral and kinetic properties of photoisomers and triplet molecules of a number of anionic polymethine dyes, namely, differential absorption spectra, rate constants (ki) and activation parameters of reversecis-trans-isomerization, and triplet-state-decay rate constantskT are studied by flash photolysis. CINDP/2 calculations of electron density in anionic dyes show thatki andkT in polar solvents are determined primarily by the electronic effect of the substituents in themeso-position of the polymethine chain of a dye. The increase inkidue to the formation of ion pairs consisting of a dye with a counterion is observed in nonpolar solvents.

Absorption, fluorescence, and fluorescence excitation spectra have been studied for a number of anionic, cationic, and cationic-anionic polymethine dyes in low-polar and nonpolar solvents, as well as in binary mixtures of solvents differing in polarity. For most of the dyes studied, fluorescent aggregates have been found to form. Their broad fluorescence bands are located in the long-wave region with respect to those of the initial dyes. The quantum yield of the aggregate fluorescence is normally higher than that of the initial dyes. Fluorescence excitation spectra of some cationic-anionic dyes in nonpolar solvents disagree with their absorption spectra because of contact and solvent-separated ion pairs simultaneously present in the solution.

Methods of synthesis of dienic δ-alkoxy-α, α-dicarbonyl-substituted compounds were experimentally examined. The structure of the synthesized compounds was studied by1H and13C-NMR methods. It was shown that the δ-alkoxy diesters are present in equilibrium with 2H-pyrans, while δ-alkoxy-γ-methyl diesters and 2-(3′-alkoxypropen-2′-ylindene)indanediones exist in an open form and do not undergo cyclization into 2H-pyrans.

Synthesis of the previously unknown bis-aminaleacetal of dimethylaminomethylenemalonaldehyde has been developed, condensation of which with malonates affords trienic δ-dimethylaminotetraesters.

The reactions of β-dimethylaminoacrolein aminals with 2,6-dimethyl-γ-pyrone lead to 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones, whose alkylation affords ethoxytridecamethine salts. The spectral and fluorescence properties of the synthesized compounds were studied. Their absorption spectra are unusual; along with the long-wavelength band in the visible spectral region, they contain a much more intense short-wavelength band in the near UV region. This pattern of the absorption spectra is explained in terms of the model of chromophore interaction, assuming an acute angle between the chromophore “halves” of the polyene chain of the dye molecule. The central pyran ring in the ethoxytridecamethine salts can hamper conjugation in the polymethine chain. Thermochromism of 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones (the long-wavelength shift of the absorption spectra on cooling of the solutions) is observed; only the long-wavelength absorption band undergoes a pronounced thermochromic shift. The introduction of methyl or phenyl substituents into the polyene chains of substituted 4H-pyranones decreases the fluorescence quantum yield.

The published data on the synthesis of β-enamino ketones, δ-amino dienones and conjugated ω-amino polyenones of diverse structures are generalised. The bibliography includes 129 references.

A reaction of 2,2-disubstituted 1,1-dicyanoethenes with β-dimethylaminoacrolein aminal and 3-dimethylamino-1,1,3-trimethoxypropane leads to substituted 6,6-dicyano-1-dimethyl-aminohexatrienes and an organic salt containing 1,1,9,9-tetracyano-2,8-diphenylnona-2,4,6,8-tetraenide as the anion and (dimethylaminopropenylidene)dimethylammonium as the cation, on the basis of which new cation-anionic polymethine dyes were obtained.