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We have obtained a new water-soluble form of boron(III) dipyrromethene luminophores using the example of 3,3',5,5'-tetraphenyl-ms-aza-2,2'-dipyrromethenate boron(III) (BODIPY) and Cremophor® (polyethylene glycol, PEG-40). The results of a study of the spectral-luminescent properties of the studied BODIPY–Cremophor®–aqueous–alcohol medium system are presented. It is found that Cremophor® is the only one of a series of investigated excipients (PEG-400, PEG-1000, polyvinylpyrrolidone, bovine serum albumin, sodium carboxymethylcellulose) providing solubilization of BODIPY in an aqueous medium, while maintaining its intense spectral characteristics, including fluorescence and luminophore, in the red region of the spectrum. The BODIPY–Cremophor® system is tested on two mouse cell lines: metastatic breast cancer and non-metastatic skin cancer. It is shown that the introduction of the BODIPY–Cremophor® system into both cell lines of mice leads to the detachment of cell cultures from the substrate and suppression of the development of cancerous tumors. The results obtained show that immobilization of BODIPY in PEG-40 in an aqueous-alcoholic medium makes it possible to obtain preparations with prolonged action, which can be used as photosensitizers (PSs) in photodynamic therapy and for bioimaging in cell biology.

The spectral luminescent properties of a series of zinc dipyrromethenate [Zn(dpm) 2 ] with alkyl-, phenyl-, meso-aza-, and halogen substituents in the ligand are studied in solutions in ethanol (neutral and acidified with hydrochloric acid). The stability of the complexes in proton-donor solvents in the ground and excited states is investigated, and quantum yields of laser-induced phototransformations are measured. In a number of cases, a relationship between the photochemical stability of the investigated dipyrromethenates and their properties in proton-donor media is found and discussed.

The effect of peripheral alkyl, aryl, and meso-aza substitution on the thermal stability of BODIPYs in an argon or oxygen atmosphere has been analyzed using thermogravimetric study results. It has been shown that an increase in the length of 2,6-alkyl substituents to seven carbon atoms is accompanied by the growth of BODIPY thermal stability by 80°C. The greatest increase in the destruction temperature of BODIPY (by 100°C) is attained via the introduction of phenyl groups in the 1,3,5,7-positions of its dipyrromethenmethene framework. meso-Aza substitution does not almost produce any effect on the thermal stability of BODIPY dyes. The BODIPY destruction beginning temperature decreases by 60–90°C in the presence of air oxygen. The thermal stability of BODIPY tends to decrease with reducing degree and symmetry of alkyl substitution in the dipyrromethene framework. A lower thermal stability of BODIPY in comparison with zinc(II) dipyrromethenates is due to the participation of fluorine atoms in intramolecular redox processes.

Photostability of B(III), Zn(II), Cd(II) complexes with monoiodo- and dibromosubstituted dipyrromethenes [BF2L] and [ML2] in benzene and cyclohexane solutions is studied. It is found that the mechanism of destruction of the dyes under UV radiation is based on participation of singlet oxygen generated by the excited triplet state of the dye. Singlet oxygen enters the oxidation reactions of the pigment molecules leading to accumulation of colorless products based on di-, monopyrrol, and smaller fragments. Initial stages of the process include the reactions of dehalogenation of the dye molecules and are accompanied by enhancement of the fluorescence of the formed alkyl-substituted dipyrromethenates. The photostability of boron complexes [BF2L] is up to 32 times higher as compared to that of [ZnL2] and [CdL2]. The replacement of 4-iododipyrromethene ligands in [BF2L] and [ML2] by 5,5'-or 4,4'-dibromo-substituted ligands increases photostability of the dyes. The stability of the dyes against UV irradiation substantially decreases in benzene with respect to cyclohexane due to enhancement of polarization of the chromophore systems of dipyrromethene ligands because of their solvation with benzene (π–π-stacking).

The complex formation of zinc(II) acetate with monoiodo- and dibromo-substituted dipyrromethenes in DMF at 298.15 K were studied by means of spectrophotometric titration. It was found that the process involves consecutive formation of heteroligand [ZnLOAc] and homoligand [ZnL2] complexes. The thermodynamic stability of halogenated zinc(II) dipyrrolylmethenates [ZnL2] was studied.

The spectral–luminescent, photophysical, and photochemical properties of dichloro-, dibromo-, and diiodo-derivatives of boron dipyrromethenate (BODIPY) have been studied, as well as the feasibility of generating singlet oxygen (1O2) via its photosensitization by the dihalogenated derivatives of BF2 dipyrromethene in solutions. Quantum yields of singlet oxygen have been determined using 1,3-diphenylisobenzofuran as the 1O2 trap. The lowest fluorescence quantum yields have been shown to correspond to the maximum yields of singlet oxygen. It has been found that the best 1O2 photosensitizer among the three test dihalotetraphenylaza- BODIPY is dibromotetraphenylaza-BODIPY, which in addition possesses the highest photostability. Diiodotetramethyl-BODIPY results in the singlet oxygen yield close to unity, but it has significantly lower photostability. The yield of singlet oxygen is affected by the solvent. Dibromtetraphenylaza-BODIPY and diiodotetramethyl-BODIPY may find use as a medium in photodynamic therapy and photocatalysis of oxidation reactions.

The results of research on the correlation between molecular structure and spectral luminescent and photophysical properties for a new class of dyes and luminophores based on dipyrrins, bis(dipyrrins), and their coordination compounds in different media are summarized. The new perspective applications of dipyrrin dyes and luminophores as fluorescent sensors for measuring the polarity, viscosity, and temperature of the medium and highly sensitive and selective fluorescent “off-on” chemosensors for detecting Zn2+, Cd2+, and Hg2+ cations in weakly polar and nonpolar organic solvents and biological systems are discussed.

The results of studies and comparative analysis of thermal properties and photostability of zinc(II) complexes with tetramethyl- and tetraphenyl-substituted dipyrrins and tetraphenyl-meso-azadipyrrin are reported. The thermal decomposition of complexes starts in the temperature range between 293 and 481°C depending on the molecular structure. Tetraphenyl-substituted zinc(II) dipyrrinate shows the highest photoand thermal stability. The substitution of phenyl moieties in the ligand structure with methyl groups and replacement of the methine spacer with a nitrogen atom reduces thermal stability and photostability of the complexes.

4-Iodo-, 4,4′-, and 5,5′-dibromo-substituted BF2-dipyrrinates (BODIPY) have been prepared, and their spectral luminescent properties and photostability have been studied. It has been shown that the introduction of iodine and bromine atoms in the molecule structure results in build-up of the BODIPY phosphorescence and decrease in their fluorescence quantum yield. Basing on the obtained data, the prepared dipyrrinates can be recommended for development of fluorescent sensors for medical and technical applications.

The spectral luminescent, photophysical, photochemical, lasing, nonlinear optical, and sensor characteristics of a series of new synthesized complexes of zinc and difluoroborate with dipyrrines of different structure have been studied. It is found that many of these compounds exhibit stimulated emission in different solvents when excited by the second (532 nm) and third (355 nm) harmonics of a Nd:YAG laser in the range of 548–692 nm. It is shown that not only efficient fluorophores belonging to dipyrrine difluoroborates (with a quantum fluorescence yield close to 1), but also compounds with a fluorescence yield equal to 0.3, generate laser radiation with a high resource; phosphorescence is also observed along with fluorescence. Transmission of UV radiation (355 nm) is shown to decrease with an increase in the pulsed excitation power density; this is a manifestation of nonlinear optical properties. The change of phosphorescence signal in dependence of the composition of the gas mixture around a solid-state sample colored by dipyrrinate complexes indicates that a number of the compounds under consideration exhibit sensor abilities.

New polymeric materials containing dinuclear double-stranded zinc(II) helicate with bis(1,2,3,7,9-pentamethyldipyrrin-8-yl)methane have been prepared on the basis of poly(methyl methacrylate) and tetraethoxysilane. The zinc(II) complex [Zn2L2] retains its fluorescence properties in a poly(methyl methacrylate) film. The photostability of [Zn2L2] in poly(methyl methacrylate) is higher by a factor of ≈2.5 than in the benzene solution. Conditions have been found for the preparation of [Zn2L2]-doped silicate matrix based on tetraethoxysilane via the sol–gel method. The [Zn2L2] complex in the tetraethoxysilane solid matrix shows a weak fluorescence with its maximum at λ = 545–549 nm.

The geometric parameters of the molecular structures of 4-monoiododipyrrine, 4,4′- and 5,5′-dibromodipyrrine complexes with zinc(II) and boron(III) of the composition [ZnL2] and [BF2L] respectively are determined at the M06 and B3LYP levels of density functional theory with the Def2-SVP basis set. The lengths of Zn–N, B–N, and B–F coordination bonds, N–X–N, F–B–F, C–C–C bond angles, the dihedral angles between the planes of pyrrole rings in the dipyrrine ligand, dipyrrine planes in [ZnL2], dipyrrine core and the plane passing through the atoms of the BF2 group are optimized. The effect of structural factors on the geometric parameters and the widths of the HOMO–LUMO energy gap in halogen substituted dipyrrinates is analyzed.

Boron(III) complexes with phenyl-substituted meso-aza-dipyrromethenes (one of them 4,4'-brominated) have been prepared. The bromination has resulted in weakening of the compound fluorescence by more than ten-fold. The studied complexes are stable for a long time in the solutions in non-polar solvents both in the dark and exposed to light. The bromine-containing complex rapidly decomposes in the polar media.

New “off-on” Zn2+ fluorescent probes in organic solvents were developed underlain by ligands consisting of deca-, octa-, and tetramethyl-substituted 3,3′-bis(dipyrrins). The coordination of the probes with two Zn2+ ions with the formation of complexes [Zn2L2] is accompanied with a significant (200–550-fold) increase in the fluorescence intensity. The fluorescence response is maximum for the reaction of Zn2+ with tetramethyl-substituted 3,3′-bis(dipyrrin). The presence of cations of Na+, Mg2+, Mn2+, Co2+, Ni2+, Cd2+, Hg2+, and other metals, save Cu2+, does not interfere with the detection of Zn2+ demonstrating the high selectivity of bis(dipyrrin) Zn2+-sensors.

A comparative study of spectral, luminescent, and photophysical parameters has been carried out for a series of zinc(II) and boron(III) chelates with dipyrromethene ligands of a similar structure: tetramethyl- and tetraphenylpyrrodimethenes bearing the substituents on the pyrrole rings and tetraphenylazapyromethene. In some cases, the luminescence efficiency of the chelates depends on the excitation wavelength. The replacement of the central atom boron(III) by zinc(II) results in not only a twofold increase in the number of coordinated chromophoric ligands and the absorption coefficient, but also an increase in the contribution of nonradiative processes to excitation energy deactivation and, hence, a decrease in the yield of fluorescence. The efficiency of intersystem crossing is higher in the zinc(II) dipyrromethene complexes than in the corresponding boron-chelated dipyrromethenes (BODIPYs), resulting in the appearance of phosphorescence in frozen solutions. It has been found that the replacement of the meso-spacer in the dipyrromethene ligand by the nitrogen atom not only shifts the absorption and fluorescence band maximums to longer wavelengths, but also decreases the fluorescence efficiency and leads to the appearance of long-lived luminescence even in aza-BODIPY. An analysis of the results has shown that these behavior can be due to involvement of the nπ* (πσ*, σπ*) states localized on the meso-nitrogen in the deactivation of excitation energy.

The crystal structure of the boron(III) complex [BF2L] synthesized for the first time, where L− is the 3,3′,5,5′-tetramethyl-4-ethyl-4′-iododipyrrolylmethene-2,2′ monoanion (iodo-BODIPY, monoclinic crystals: a = 12.0329(6) A, b = 15.9657(8) A, c = 8.5080(4) A, β = 103.753(1)°, V = 1587.64(13) A3, Z = 4 (Z′ = 1), space group P21/c) is determined. In the structure, two pyrrol rings and the central six-membered ring containing a boron atom are in one plane, perpendicular to which a plane formed by a group of F-B-F atoms is located. The crystal packing is formed by van der Waals interactions. In the electron absorption spectra of iodo-BODIPY solutions in nonpolar solvents, unlike polar ones, a red shift up to 3–8 nm of the maximum of the first intense band is observed, for which the lgɛ value reaches ∼4.71. Along with intense chromophoric properties, the synthesized iodo-BODIPY complex is a sufficiently strong fluorophore and can be used as a fluorescent marker.

Effect of complexing atom, molecular structure of dipyrrolylmethene and its aza analog on spectral-luminescent properties of heteroleptic boron(III) and homoleptic zinc(II) complexes with 3,3′,5,5′-tetramethyl-2,2′-dipyrrolylmethene, 3,3′,5,5′-tetraphenyl-2,2′-dipyrrolylmethene, and 3,3′,5,5′-tetraphenyl-ms-aza-2,2′-dipyrrolylmethene in organic solvent solutions was studied. The complexes were found to exhibit strong chromophore (λ = 350–690 nm, ɛ ∼ 105 L/mol cm) and fluorescent properties. Quantum yield (γfl) for fluoroborate complexes reaches 100% and is weakly dependent on medium nature. The value of γfl for phenyl- and alkyl-substituted zinc(II) dipyrrolylmethenates in nonpolar solvents is not higher 0.3 and 0.03, respectively; complete fluorescence quenching is observed in electron-donating solvents. Aza-substitution at the meso spacer causes considerable shift of electronic absorption and fluorescence spectra to the red region but completely quenches fluorescence of zinc(II) chelates and decreases γfl of boron(III) complex to 0.04.

A kinetic model and a mechanism have been developed by quantum chemical simulation for the protolytic dissociation of dinuclear homoleptic bis(dipyrrolylmethenates) of d-metals (M) with the general formula [M2L2] and a double-helix structure. The reaction is described by a third-order equation that is first-order with respect to the complex and second-order with respect to the acid. The main contribution to the total dissociation rate is made by the rate-determining step, specifically, attack of the second acetic acid molecule on the nitrogen atom of one of the coordination sites of the helicate. The dinuclear helicates of 3,3′-bis(dipyrrolylmethenes) are more inert in an acidic medium than 2,3′- and 2,2′-bis(dipyrrolylmethenes).

The effect of the attachment position of a methylene spacer in 2,2′-, 2,3′-, and 3,3′-bis(dipyrromethene) N4-ligands (H2L) on physicochemical properties of their dinuclear homoleptic helicates [Zn2L2], such as specific features of their molecular structure, luminescence spectral characteristics, lability in acid solutions, and thermal stability in an argon atmosphere, has been examined. It has been shown that the substitution of the biladiene-type helicand by its 2,3- and especially 3,3′-analogues leads to a considerable enhancement of the chromophoric properties, an increase (up to 30-fold) of the fluorescence quantum yield, and an increase in the stability of corresponding dinuclear helicates [Zn2L2].

Quantum chemical calculations of the molecular structure of bis(dipyrrolylmethanates) of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), and mercury(II) of the composition [M2L2] are performed using the PM6 method within the Gaussian 09W program package. The lengths of M-N coordination bonds, the values of dihedral angles formed by N-M-N bonds, the distances lM⋯M between the M⋯M atoms are optimized. It is noted that the regularities obtained from the analysis of the results of quantum chemical calculations of the molecular structure of [M2L2] helicates reliably reflect the main trends of changes in their physicochemical properties depending on the nature of a complexing agent and the features of the ligand structure.

Using fluorescence and electronic spectroscopy the interaction of boron-dipyrromethene complex (BODIPY) with bovine serum albumin (BSA) and its bilirubin macromolecular complex (BR·BSA) in aqueous solution was investigated. The interaction of BODIPY is carried out by the static quenching of protein fluorescence and is predominantly hydrophobic and electrostatic in nature. The values of the binding constants were (61.2 ± 2.8) · 103 and (6.51 ± 0.3) · 103 M−1. The interaction of BODIPY with proteins leads to the observed hypso- and bathochromic shift in BODIPY absorption band. Forster resonance energy transfer theory allowed of determing the donor-ligand distance, which were 2.88 and 2.46 nm for BSA and BR·BSA, respectively. Using synchronous fluorescence spectroscopy it was possible to reveal features of BODIPY influence on conformational changes in protein molecules. It was established that BODIPY more effectively interacts with BSA compared to BR·BSA.

Luminescence study of the reaction of 3,3′-methanediylbis(2,4,7,8,9-pentamethyldipyrrolylmethene) (H2L) with a number of metal salts showed that this compound is an efficient fluorescent chemosensor for Zn2+ ions in organic solvents. The selectivity and sensitivity of H2L were estimated in various solvents in the presence of other metal cations (Na+, Mg2+, Co2+, Ni2+, Cu2+, Cd2+, Hg2+, Pb2+).

We have studied the spectral-luminescent, lasing, photochemical, and endurance characteristics of a series of new efficiently emitting difluorine borate complexes with dipyrrolylmethenes of different structures. Experimental data have been obtained in polar and nonpolar organic solvents and in solid polymer films involving the participation of silicate structures. We have discussed relations of the structure of investigated compounds and formed solvates with their optical characteristics, and have given guidelines on the use of particular compounds as active media of tunable lasers for determining spectral ranges.

Protolytic dissociation of copper(II) and nickel(II) dipyrrolylmethenates in benzene solutions of acetic acid has been studied. The results have completed the knowledge of kinetics of dipyrrolylmethene complexes dissociation in acidic medium. The effect of the nature of complex forming atom, ligand, and other factors on the complexes kinetic stability has been analyzed.

Complexes [ML2] of cobalt(II), nickel(II), copper(II), zinc(II), and cadmium(II) with asymmetrically substituted (E)-3-ethyl-5-[(4-iodo-3,5-dimethyl-2H-pyrrol-2-ylidene)methyl]-2,4-dimethyl-1H-pyrrole (HL) have been prepared and characterized for the first time. The spectral properties, stability in solutions and in the solid phase at elevated temperature of the complexes have been studied. The effects of complexing metal ion and the reaction medium on the spectral luminescent properties (absorptivity, quantum yield, fluorescence lifetime, and the radiation constant) and on thermal destruction of the [ML2] complexes have been discussed.

The study and comparative analysis of spectral-luminescent characteristics (absorption and fluorescence spectra), of quantum yield, and fluorescence life time in solutions, of lability in proton-donor media, solid phase thermal stability in air oxygen and argon was carried out for binuclear zinc(II) helicates with decamethyl-substituted 2,3′- and 3,3′-bis(dipyrrolylmethenes). The influence of molecular structure features of the ligands on the physicochemical properties of helicates was discussed.

The trends of kinetic resistance of borofluoride complexes of alkyl- and sulfo-substituted dipyrrolylmethene (Bodipy) to protolytic and solvoprotolytic dissociation in organic solvents and aqueous solutions are studied. It is established that among dipyrrolylmethene complexes with d elements, Bodipy is notable for its superresistance to acids. The rate of the dissociation reaction increases with increasing acidity of protonating mixtures or decreasing effective charge of the coordinating nitrogen atoms of the ligand. Dissociation of the complexes occurs in accordance with a second-order rate equation. A kinetic model of the process is proposed; its kinetic and activation parameters are determined. The energy profiles of the initial stages of protolytic dissociation reactions are calculated using quantum-chemical methods for two suggested variants of the transient state; the energetically preferable pathway is recognized.

Using spectrophotometry we found that ligand exchange in the systems of H2L-[MX2]-DMF, where M denotes Co2+, Cu2+, and Zn2+; X means Acac−, Val−, dpm−; Hdpm− is hexamethyldipyrrolylmethene, H2L is bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)methane, proceeds through successive stages of formation of hetero- and homoleptic binuclear complexes. Conventional sensitivity of the spectrophotometric determination of Co2+, Cu2+, and Zn2+ reaches 10−9 M.

Thermal oxidative decomposition of samples of crystalline hydrobromide and borofluoride complexes (BODIPY) of a series of 2,2′-dipyrrolylmethenes (HL) was studied by means of thermogravimetry in an atmosphere of air oxygen. An increase in the degree and symmetry of substitution, aromaticity, and the length of the substituents in 4,4′-positions of the pyrrole ligand rings increases stability of the BODIPY-dyes to oxidative degradation. A comparative analysis of the influence of structural factors on the thermolability of hydrobromdes (HL·HBr), d-metal (ML2) and boron(III) complexes with 2,2′-dipyrrolylmethenes was carried out.

Palladium(II) complexes with alkylated dipyrrolylmethene (Hdpm) and its bis-derivative, biladienea, c (H2bd), of the composition [Pd(dpm)2] and [Pd(bd)] were synthesized and were characterized by IR, UVVIS, and NMR spectroscopy. It was shown that the nature of the solvent has almost no effect on the spectral characteristics of the complexes due to the square-planar configuration of the coordination nodes in them and, respectively, the impossibility of further coordination. From the results of the kinetic study of the complexes stability to the action of acids in the C6H6-CCl3COOH mixtures it was concluded that the Pd(II) complexes are much more stable compared to the other d-metal dipyrrolylmethenates. Kinetic manifestation of polychelate effect was observed consisting in a sharp decrease in the dissociation rate of the palladium(II) complex with biladiene as compared to that with dipyrrolylmetene.

A hybrid material based on polymethylmethacrylate with immobilized borofluoride dipyrrolylmethene complex. The inclusion of the chromophore in the polymer environment is shown to result in a reduced polarization due to the weakening of the forces of intermolecular interactions. Study of spectral properties, photo and thermal stability showed that inclusion of the complex in the polymer matrix can significantly increase the photo and thermal stability and mechanical strength of the material while preserving the spectral characteristics inherent to the individual compound.

A comparative study of the dissociation of zinc(II) helicates with a series of 3,3′-bis(dipyrrolylmethenes) (H2L) of [Zn2L2] composition in acetic acid-benzene binary proton donor solvent in the temperature range from 298.15 to 318.15 K is performed by means of electronic spectroscopy. Quantitative kinetic characteristics are determined and a stoichiometric mechanism of reaction is suggested. It is established that the protolytic dissociation of [Zn2L2] helicates proceeds according to a third-order kinetic equation of reaction. The effect of alkyl substituents in the pyrrol rings and nature of central 3,3′-spacer on lability of helicates is analyzed.

(1,2,3,7,9-pentamethyldipyrrolylmethen-8-yl)(1,2,3,7,8-pentamethyldipyrrolylmethen-9-yl)-methane and bis(1,2,3,7,9-pentamethyldipyrrolylmethen-8-yl)trifluoromethylmethane hydrobromides were synthesized and characterized spectrally (1H NMR, IR, electron absorption spectra). A comparative study was performed of the effect of the bonding site (α- or β-position of the dipyrrolylmethene) with the methane structural fragment connecting two dipyrrolylmethene chromophores, and trifluoromethyl group on the spectral properties of the molecules of compounds dissolved in organic solvents of different nature and their resistance to thermal oxidative degradation.

The published data on the crystal solvates with nonpolar aromatic and electron-donor compounds obtained using different research methods as well as our own experimental results obtained by thermogravimetric analysis of the porphyrins and metalloporphyrins of natural and synthetic origin are generalized. The influence of the molecular structure of the porphyrins and metalloporphyrins on the composition, structural parameters, thermal and energy stability of crystal solvates formed through specific σ-and π-complexes with molecular ligands are considered.

The kinetics of dissociation of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) binuclear homoleptic double-stranded helicates with bis(2,4,7,8,9-pentametyldipyrrolylmethen-3-yl)methane (H2L) of the [M2L2] composition in the binary proton-donor solvent acetic acid-benzene was studied. Protolytic dissociation of the helicates [M2L2] proceeds in accordance with the third order kinetic equation. Effect of the complexing metal nature is manifested in increased kinetic inertness in the following series of the helicates: [Cd2L2] < [Hg2L2] < [Cu2L2] < [Ni2L2] < [Zn2L2] < [Co2L2]. By the lability in similar environmental conditions the helicates [M2L2] are comparable to the metal complexes of distorted porphyrins and are much more inert than dipyrrolylmethenate mononuclear complexes.

Spectral and photophysical characteristics of borofluoride complex of alkylated dipyrromethene (Bodipy) are determined by means of absorption and fluorescence electron spectroscopy in various organic solvents. Dependences of the spectral and photophysical characteristics of Bodipy solutions vs. the physico-chemical parameters of solvents are obtained by linear regression analysis and the contribution from each parameter to the property under study is determined. It is established that the negative solvatochromic effect is intrinsic for Bodipy. It is concluded that specific interactions contribute substantially to the properties of the chromophore, which are determined by the electron donor properties of the solvent.

The results of a comparative study of the oxidation of bilirubin, ascorbic acid, and their mixture in aqueous solutions under the action of air oxygen and hydrogen peroxide are presented. The observed and true rate constants for the oxidation reactions were determined. It was shown that the oxidation of tetrapyrrole pigment occurred under these conditions bypassing the stage of biliverdin formation to monopyrrole products. Simultaneous oxidation of bilirubin and ascorbic acid was shown to be accompanied by the inhibition of ascorbic acid oxidation by bilirubin, whereas ascorbic acid itself activated the oxidation of bilirubin.

Thermal effects of the reactions of complex formation between d- and f-elements and 3,3′,5,5′-tetramethyl-4,4′-diethyl-2,2′-dipyrrolylmethene in dimethylformamide are determined from data of titration microcalorimetry and the temperature behavior of the complex formation equilibrium constants. The entropy and free energy changes of the complex formation reactions are calculated. It is shown that enthalpy-entropy compensation is observed for complex formation processes in all cases. Contributions from the enthalpy and entropy factors to the free energy change of the complex formation are analyzed, allowing us to confirm earlier conclusions as to the effect of the nature of a complexing agent on the relative percentage of covalent and ionic characters of the M-L bond. The dependence of the complex formation enthalpies on the inverse radius of a complexing agent is revealed for the lanthanide complexes.

We have studied the spectroscopic and lasing characteristics of active media based on two synthesized boron fluoride complexes of alkyl-substituted dipyrrolylmethenes and the photostability of the complexes in comparison with complexes of this kind that were previously studied in the literature under identical excitation conditions. We have determined and analyzed conditions under which new compounds have either merits or drawbacks as compared to the known dye with respect to both lasing efficiency and resource characteristics.

On the basis of spectrophotometric studies, it was demonstrated that complexation of hydrobromides of seven alkylated 3,3′-bis(dipyrrolylmethenes) (H2L · 2HBr) with zinc(II) acetate dihydrate in DMF (298.15 K) includes successive steps of formation of binuclear helicates of two types: [Zn2(AcO)2L] (heteroleptic single-helix complex) and [Zn2L2] (homoleptic double-helix complex). An increase in the degree of alkylation of the pyrrole rings of the ligands from 4 to 10 methyl groups induces an increase of overall complexation constants from 7.60 to 13.73. The synthesis of helicates [Zn2L2] was described. The products were studied by elemental analysis and IR, 1H NMR, U/Vis, and fluorescence spectroscopy. The effect of the helicand structure and the solvent nature on the chromophore and fluorescence properties of [Zn2L2] was discussed. The kinetic stability of zinc(II) with decamethyl-substituted 3,3′-bis(dipyrrolylmethene) in HCl-DMF medium was estimated.

Influence of structure on the thermal properties of a large group of natural and synthetic porphyrins (H2P) and metalloporphyrins (MP) was analyzed on the ground of thermogravimetric studies. The initial stage of thermal degradation of “classical” porphyrin containing a flat or pseudo-planar macrocycle is a result of oxidative degradation of the macrocyclic structure with the formation of linear tetrapyrrols. The negative effect on the thermal stability of porphyrins exerts the violation of the planar structure of the macrocycle, and the presence of bulky alkyl and polar pseudoalkyl substituents. In many cases, the general trend in the decrease in the stability of metalloporphyrins (MP) in comparison with the corresponding H2P is a consequence of intramolecular metal ↔ ligand redox processes.

The reactions of seven symmetrically alkylated tetradentate ligands 3,3′-bis(dipyrrolylmethenes) (H2L) with d-metal acetates (M(AcO)2) in DMF solutions at 298.15 K were studied by spectrophotometry. Helicands H2L were found to be structurally preorganized to form stable binuclear homoleptic two-helix helicates [M2L2] with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates. The coordination of the ligands by the metal ions included consecutive stages of formation of the heteroleptic [M2L(AcO)2] and homoleptic [M2L2] complexes. The [M2L(AcO)2] complexes were spectrally revealed in solutions containing a ligand excess (cH2L / cM(AcO)2 > 1). An increase in the salt concentration shifted the system of equilibria to the homoligand product [M2L2]. The thermodynamic constants of the reactions increased in the series of complexing agents: Cu(II) < Cd(II) < Hg(II) < Ni(II) < Co(II) < Zn(II). An analysis of the data on the thermodynamic constants of [M2L2] helicate formation in solutions and the earlier obtained results of the IR and 1H NMR studies of the hydrobromic salts of the ligands (H2L · 2HBr) showed that the key regularities of the influence of the structural factors on the coordination properties of the ligands were in an increase in the stability of the [M2L2] complexes with an increase in the basicity of the ligands.

The geometric parameters and energies of the products of donor-acceptor interaction of dipyrrolylmethenes with BF3 and other inorganic Lewis acids were calculated by quantum-chemical methods. The bond nature and the energies of formation of the donor-acceptor complexes under consideration were analyzed. It was shown that the complexes with p-element fluorides are noticeably stabilized by hydrogen bonds involving the hydrogen atom of the NH group of dipyrrolylmethene and the nearest fluorine atom of a Lewis acid. Hydrogen bonding promotes further elimination of HF in the synthesis of boron fluoride complexes of dipyrrolylmethenes. The energy profile was calculated for the reaction of formation of the boron fluoride complex with dipyrrolylmethene through the intermediate donor-acceptor complex.

Intermediate products of synthesis of the boron trifluoride complexes with linear oligopyrroles are found. By means of electronic spectroscopy it was shown that the reaction of linear oligopyrroles with boron trifluoride in solutions resulted in the formation of stable donor-acceptor complexes. Their composition was established and the formation constants were evaluated. It was shown that transformation of these complexes in the corresponding borofluoride complexes is possible only while boiling the reaction mixture. By means of quantum-chemical methods the structural and energy parameters of the donor-acceptor complexes under study were calculated.

3,3′-Bis(dipyrromethene) dihydrobromides (H2L · 2HBr) with various types of alkylation have been synthesized. On the basis of IR, 1H NMR, and electronic absorption spectra, spectrophotometric titration, and thermogravimetry, conclusions have been drawn about the influence of structural factors on the optical and thermal properties and salt stability in solutions. An increase in the degree of alkylation causes a significant high-frequency shift of the N-H stretching vibration band in the IR spectra, an upfield shift of the 1H NMR signals of NH protons, a decrease in the auxochromic effects of protons on the aromatic system of the chromophore, and an increase in the salt stability in solutions in the presence of nucleophilic reagents and in the thermal stability in air and argon.

It has been found with the use of electronic spectroscopy that the reaction of alkyl-substituted 2,2′-dipyrrolylmethene with La(III), Pr(III), Sm(III), Dy(III), Ho(III), Er(IIII), and Yb(III) salts leads to the formation of tris(dipyrrolylmethene) complexes. Based on electronic absorption spectroscopy data and formation constants of lanthanide complexes, together with the earlier data, analysis of the nature of M-L bonds in 2,2′-dipyrrolylmethene chelates with p, d, and f elements has been performed. A correlation was found between the complex stability and the polarizing action of the complex-forming ion on the chromophore π system of dipyrrolylmethene, which allows one to classify these heterocyclic ligands with probes highly sensitive to the change in the ratio between the ionic and covalent contributions to coordination interactions.

A comparative study of oxidation reactions of bilirubin and its complex with albumin was carried out in aqueous solutions under the action of hydrogen peroxide and molecular oxygen at different pH values. Free radical oxidation of the pigment in both free and bound forms at pH 7.4 was shown not to lead to the formation of biliverdin, but to be associated with the decomposition of the tetrapyrrole chromophore into monopyrrolic products. The effective and true rate constants of the reactions under study were determined. It was assumed that one possible mechanism of the oxidation reaction is associated with the interaction of peroxyl radicals and protons of the NH groups of bilirubin molecules at the limiting stage with the formation of a highly reactive radical intermediate. The binding of bilirubin with albumin was found to result in a considerable reduction in the rate of the oxidation reaction associated with the kinetic manifestation of the protein protection effect. It was found that the autoxidation of bilirubin by molecular oxygen with the formation of biliverdin at the intermediate stage can be observed with an increase in the pH of solutions.

The reactions of protonated (H4L2+) and free (H2L) forms of the ligand 1,2,3,7,8,12,13,17,18,19-decamethylbiladien-a,c with zinc(II) acetate in dimethyl sulfoxide was studied by the spectrophotometric method. It was found that the mononuclear complex [ZnL] is formed in the studied systems. Constants of its formation were determined from the spectral data. Unlike H2L, the protonated [H4L2+] form has extremely low reactivity, because the initial stages of the complex formation mechanisms of the free and protonated forms of the ligand are different. Regularities of the solvent nature influence on the free energy of formation of biladien chelates were revealed.

The reactions of symmetric and nonsymmetric alkyl-substituted 2,2′-dipyrrolylmethenes with Cu(II), Ni(II), Co(II), Zn(II), Cd(II), and Hg(II) acetates in dimethylformamide solutions at 298.15 K were studied. The formation of hetero- and homoligand complexes was observed in the systems studied depending on the concentration conditions and the nature of the complexing metal. The stepped and complete constants of formation for metal complexes were determined. The key trends of the influence of the metal and ligand nature on the stabilization of the complexes were established.

Four new alkyl-substituted 3,3′-bis(dipyrrolylmethene) dihydrobromides containing from 4 to 10 alkyl substituents were synthesized. In a highly alkylated ligand of these substances one of the hydrogen atoms of the 3,3′-methylene spacer was substituted with a phenyl group. The compounds obtained were studied by IR, 1H NMR, electron absorption, and fluorescent spectroscopy. The increased alkylation degree of pyrroles and the introduction of an aryl substituent in the 3,3′-spacer causes a significant high-frequency shift of the N-H stretching vibrations in the IR spectra, an upfield shift of the NH-proton signals in 1H NMR spectra, a decrease in the auxochromic effects of protons on the aromatic system of chromophore in the composition of salts. The red shift of maximum of the strong band in electron absorption spectra and the emission spectra of compounds in DMF, DMSO, C5H5N, C6H6, and CHCl3 was established. The salts obtained are stable in benzene and chloroform, while in electron-donor solvents the irreversible processes of solvolytic dissociation of salts to free organic base and HBr take place.