Main Absorption Maximum Research Articles

Multicomponent Synthesis of New Fluorescent Boron Complexes Derived from 3-Hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde.

Novel fluorescent pyrazole-containing boron (III) complexes were synthesized employing a one-pot three-component reaction of 3-hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde, 2-aminobenzenecarboxylic acids, and boronic acids. The structures of the novel heterocyclic compounds were confirmed using 1H-, 13C-, 15N-, 19F-, and 11B-NMR, IR spectroscopy, HRMS, and single-crystal X-ray diffraction data. The photophysical properties of the obtained iminoboronates were investigated using spectroscopic techniques, such as UV-vis and fluorescence spectroscopies. Compounds display main UV-vis absorption maxima in the blue region, and fluorescence emission maxima are observed in the green region of the visible spectrum. It was revealed that compounds exhibit fluorescence quantum yield up to 4.3% in different solvents and demonstrate an aggregation-induced emission enhancement effect in mixed THF-water solutions.

Analysis of Spectral Characteristics of Certain Polyene Antibiotics in the Presence of Dmso and Cholesterol

This work presents ultraviolet (UV) spectra of various concentrations of polyene antibiotics. The spectra of Levorin and Amphotericin B differ in three main absorption maxima. The maximum absorption spectra of antibiotics vary in the range of 370–430 nm. UV absorption spectra reflect the characteristic spectrum of polyenes belonging to this class. Amphotericin B and Levorin in combination with cholesterol lower the maximum of the UV absorption spectra. Analysis of the obtained results shows that cholesterol molecules, combining with double-bond systems of Amphotericin B and Levorin, gradually reduce the maximum absorption of UV spectra, which creates opportunities for their more active use in various fields of biomedicine.

Photogeneration and quenching of singlet molecular oxygen by bacterial C40 carotenoids with long chain of conjugated double bonds.

Measurement of photosensitized luminescence of singlet oxygen has been applied to studies of singlet oxygen generation and quenching by C40 carotenoids (neurosporene, lycopene, rhodopin, and spirilloxanthin) with long chain of conjugated double bonds (CDB) using hexafluorobenzene as a solvent. It has been found that neurosporene, lycopene, and rhodopin are capable of the low efficient singlet oxygen generation in aerated solutions upon photoexcitation in the spectral region of their main absorption maxima. The quantum yield of this process was estimated to be (1.5-3.0) × 10-2. This value is near the singlet oxygen yields in solutions of ζ-carotene (7 CDB) and phytoene (3 CDB) and many-fold smaller than in solutions of phytofluene (5 CDB) (Ashikhmin et al. Biochemistry (Mosc) 85:773-780, https://doi.org/10.1134/S0006297920070056 , 2020, Biochemistry (Mosc) 87:1169-1178, 2022, https://doi.org/10.1134/S00062979221001082022 ). Photogeneration of singlet oxygen was not observed in spirilloxanthin solutions. A correlation was found between the singlet oxygen yields and the quantum yields and lifetimes of the fluorescence of the carotenoid molecules. All carotenoids were shown to be strong physical quenchers of singlet oxygen. The rate constants of 1O2 quenching by the carotenoids with long chain of CDB (9-13) were close to the rate constant of the diffusion-limited reactions ≈1010M-1s-1, being many-fold greater than the rate constants of 1O2 quenching by the carotenoids with the short chain of CDB (3-7) phytoene, phytofluene, and ζ-carotene studied in prior papers of our group (Ashikhmin et al. 2020, 2022). To our knowledge, the quenching rate constants of rhodopin and spirilloxanthin have been obtained in this paper for the first time. The mechanisms of 1O2 photogeneration by carotenoids in solution and in the LH2 complexes of photosynthetic cells, as well as the efficiencies of their protective action are discussed.

GOSSIPOL AND ITS DERIVATIVES: SYNTHESIS, MODIFICATION AND STRUCTURE

The article provides information on the synthesis of new derivatives of gossypol, their modification in order to obtain water-soluble complexes, as well as the analysis of their physicochemical and structural properties. In the above work, three iminoazo derivatives of gossypol were synthesized for the first time, on the basis of which water-soluble complexes were obtained. In the synthesis of gossypol derivatives, heterylamines were used as substituents on the aldehyde group and on the C-4 atoms of gossypol. The physicochemical properties of the synthesized water-soluble complexes were studied by UV and IR spectrometric methods and their structure was analyzed.
 A comparative analysis of the UV spectra of iminoazo derivatives and complexes of gossypol derivatives with poly-N-vinylpyrrolidone (N-PVP) showed a slight shift in the main absorption maxima. In addition, various electronic transitions associated with functional groups in gossypol derivatives and N-PVP molecules were observed. This suggested that a complex compound was formed. In order to confirm the structure of the complexes of iminoazo derivatives of gossypol with N-PVP, a comparative study of them with intermediate compounds by IR spectroscopic analysis was carried out and the most probable structures of the obtained compounds were shown.

Chirality of small niobium clusters

We report on time-dependent density functional theory calculations to study the chiroptical properties of small $$\hbox {Nb}_{{9}}$$ clusters and their corresponding van der Waals $$\hbox {Nb}_{{9}}\hbox {Ar}_{n}$$ complexes. The three most stable 9-atom structures considered in the literature are analyzed, and we obtain their lowest-energy atomic configurations, UV–Vis response, and for the first time, the electronic circular dichroism (ECD) spectra of the systems. Excitation energies, as well as oscillator and rotational strengths are calculated using the M06 exchange-correlation functional together with a mixed basis approach where all electron DGDZVP and Def2SV basis are employed for Nb and Ar atoms, respectively. In all cases, the UV–Vis spectra look very similar and are characterized by the formation of a main absorption maxima located at $$\sim 240\hbox { nm}$$ ; however, the distribution of simulated ECD signals strongly depends on the geometrical structure of the clusters. Our calculated ECD bands show precise features that cover the experimentally accessible 200–300 nm range and extend near the visible part of the spectra, a fact that allows us to distinguish between different niobium cluster geometries. However, weighted averages of calculated ECD spectra for different $$\hbox {Nb}_{{9}}$$ clusters reveal that isomerization effects might lead to a notable increase/reduction in the intensity of CD lines since the simulated bands could add or cancel each other.

A chemodosimeter approach for selective colorimetric and fluorimetric cyanide detection using coumarin based fluorescent dyes

New coumarin based allylidenemalononitrile-aminophenyl conjugated fluorescent dyes having donor-π-acceptor-donor (D-π-A-D) system (Dyes 1, 2 and 3) were synthesized and characterized using 1H/13C-APT NMR and HRMS. Interestingly, dye 3 (diacetamide derivative) was obtained as a mixture of E/Z isomer. Dye 3 was investigated by 1H NMR within two solvents with different polarity (DMSO-d6 and Chl-d1) and exposed UV irradiation to observe any configurational changes. The absorption and emission properties of the dyes were determined in various solvents with different polarity. The anion sensitivity and selectivity of the dyes were studied with various anions in DMSO, and their interaction mechanisms were evaluated by spectrophotometric and 1H NMR titration techniques. All three dyes only interacted with cyanide via Michael reaction and the main absorption maxima showed hypsochromic shifts and emission intensity quenched. Moreover, investigation of cyanide sensitivity of the dyes was studied in aqueous media as a mixture of DMSO:water (7:3, v/v). Also, all these results can be detected with the naked eye due to the observed color of the dyes changes from pink to yellow. Additionally, DFT and TDDFT studies were performed to support structural and absorption spectral properties of the dyes.

Optical Properties of Thin Films of Zinc Phthalocyanines Determined by Spectroscopic Ellipsometry

The optical properties of thin films based on unsubstituted and tetrafluoro-substituted zinc phthalocyanines synthesized by physical vapor deposition are studied within the wavelength range of 250–1000 nm. Spectroscopic ellipsometry shows that films based on zinc phthalocyanines have uniform thicknesses and optical parameters, strongly absorb visible light, and have characteristic absorption peaks corresponding to electronic transitions in the system of conjugated double bonds of phthalocyanine rings. Introduction of fluorine substituents into peripheral positions of the zinc phthalocyanine molecule leads to an increase in light absorption and a shift of the main absorption maximum to longer wavelengths (bathochromic shift). The absorption spectra are described using the Lorentz–Drude dispersion model. It is shown that the films based on a mixture of phthalocyanines can be well described using the Bruggeman effective medium model.

Coumarin-indole conjugate donor-acceptor system: Synthesis, photophysical properties, anion sensing ability, theoretical and biological activity studies of two coumarin-indole based push-pull dyes

Two coumarin-indole conjugate fluorescent dyes having donor-acceptor-donor (D-A-D) (CI-1 and CI-2) were synthesized, and characterized using IR, 1H/13C NMR and HRMS. The absorption and emission properties of the dyes were determined in different solvents. The anion sensitivity and selectivity of the dyes were studied with some anions (CN−, F−, AcO−, Cl−, Br−, I−, HSO4− and H2PO4−) in DMSO, and their interaction mechanisms were evaluated by spectrophotometric and 1H NMR titration techniques. In addition, the molecular and electronic structures of CI-1, as well as the molecular complexes of CI-1, formed with the anions (F− and AcO−), were obtained theoretically and confirmed by DFT and TD-DFT calculations. CI-1 behaves as a colorimetric chemosensor for selective and sensitive detection of CN− in DMSO/H2O (9:1) over other competing anions such as F− and AcO−. However, only CN− interacts with chromophore CI-2 via Michael addition and the main absorption maxima shifts hypsochromically with an observed distinctive color change from orange to yellow. For using as a optic dye, the thermal stability properties of the dyes was determined by TGA (Thermal Gravimetric Analysis). Antimicrobial, antifungal and DNA-ligand interaction studies of the dyes were also examined. The dyes cause conformational changes on DNA and selectively bind to nucleotides of A/A and G/G.

The IR Spectra, Molar Absorptivity, and Integrated Molar Absorptivity of the C76-D2and C84-D2:22 Isomers

The FT-IR spectra of the stable C76and C84isomers of D2symmetry, isolated by the new, advanced extraction and chromatographic methods and processes, were recorded by the KBr technique, over the relevant region from 400 to 2000 cm−1, at room temperature. All the observed infrared bands are in excellent agreement with the semiempirical QCFF/PI, DFT, and TB potential calculations for these fullerenes, which is presented in this article, as the evidence of their validity. The molar absorptivityεand the integrated molar absorptivityψof their IR absorption bands were determined and reported together with the relative intensities. Excellent agreement is found between the relative intensities of the main and characteristic absorption maxima calculated fromελand from theψλvalues in adequate integration ranges. These results are significant for the identification and quantitative determination of the C76-D2and C84-D2:22 fullerenes, either in natural resources on Earth and in space or in artificially synthesized and biomaterials, electronic, optical, and biomedical devices, sensors, polymers, optical limiters, solar cells, organic field effect transistors, special lenses, diagnostic and therapeutic agents, pharmaceutical substances in biomedical engineering, and so forth.

Composite biodegradable biopolymer coatings of silk fibroin – Poly(3-hydroxybutyric-acid-co-3-hydroxyvaleric-acid) for biomedical applications

Composite silk fibroin–poly(3-hydroxybutyric-acid-co-3-hydroxyvaleric-acid) (SF–PHBV) biodegradable coatings were grown by Matrix Assisted Pulsed Laser Evaporation on titanium substrates. Their physico-chemical properties and particularly the degradation behavior in simulated body fluid at 37°C were studied as first step of applicability in local controlled release for tissue regeneration applications.SF and PHBV, natural biopolymers with excellent biocompatibility, but different biodegradability and tensile strength properties, were combined in a composite to improve their properties as coatings for biomedical uses.FTIR analyses showed the stoichiometric transfer from targets to coatings by the presence in the spectra of the main absorption maxima characteristic of both polymers. XRD investigations confirmed the FTIR results showing differences in crystallization behavior with respect to the SF and PHBV content. Contact angle values obtained through wettability measurements indicated the MAPLE deposited coatings were highly hydrophilic; surfaces turning hydrophobic with the increase of the PHBV component. Degradation assays proved that higher PHBV contents resulted in enhanced resistance and a slower degradation rate of composite coatings in SBF. Distinct drug-release schemes could be obtained by adjusting the SF:PHBV ratio to controllably tuning the coatings degradation rate, from rapid-release formulas, where SF predominates, to prolonged sustained ones, for larger PHBV content.

New approach to measurement of IR absorption spectra of dissolved oxygen molecules based on photochemical activity of oxygen upon direct laser excitation

Generation of singlet oxygen upon excitation of oxygen molecules with IR diode lasers has been studied in organic media (carbon tetrachloride and acetone) saturated with air under normal pressure and temperature. A new approach to analysis of the experimental data has been developed, which takes into account the degree of overlapping of the spectral bands of oxygen absorption and laser radiation. Optical density, molar absorption coefficient, and the cross section of light absorption were determined for the main absorption maxima of O2 at 765 and 1273 nm. The results are compared with the data of previous studies. Significance of these results for elucidation of photophysics and photochemistry of oxygen molecules and investigation of biological action of laser radiation is discussed.

Synthesis, Spectroscopic Properties, and Photoinduced CO-Release Studies of Functionalized Ruthenium(II) Polypyridyl Complexes: Versatile Building Blocks for Development of CORM–Peptide Nucleic Acid Bioconjugates

A series of ruthenium(II) dicarbonyl complexes of formula [RuCl2(L)(CO)2] (L = bpy(CH3,CH3) = 4,4'-dimethyl-2,2'-bipyridine, bpy(CH3,CHO) = 4'-methyl-2,2'-bipyridine-4-carboxyaldehyde, bpy(CH3,COOH) = 4'-methyl-2,2'-bipyridine-4-carboxylic acid, CppH = 2-(pyridin-2-yl)pyrimidine-4-carboxylic acid, dppzcH = dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylic acid), and [RuCl(L)(CO)2](+) (L = tpy(COOH) = 6-(2,2':6',2″-terpyridine-4'-yloxy)hexanoic acid) has been synthesized. In addition, a high-yield synthesis of a peptide nucleic acid (PNA) monomer containing the 2-(pyridin-2-yl)pyrimidine ligand was also developed, and this compound was used to prepare the first Ru(II) dicarbonyl complex, [RuCl2(Cpp-L-PNA)(CO)2],(Cpp-L-PNA = tert-butyl-N-[2-(N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2-yl)pyrimidine-4-carboxamido)hexanoyl]glycinate) attached to a PNA monomer backbone. Such metal-complex PNA-bioconjugates are attracting profound interest for biosensing and biomedical applications. Characterization of all complexes has been undertaken by IR and NMR spectroscopy, mass spectrometry, elemental analysis, and UV-vis spectroscopy. Investigation of the CO-release properties of the Ru(II) complexes in water/dimethyl sulfoxide (49:1) using the myoglobin assay showed that they are stable under physiological conditions in the dark for at least 60 min and most of them even for up to 15 h. In contrast, photoinduced CO release was observed upon illumination at 365 nm, the low-energy shoulder of the main absorption maximum centered around 300 nm, establishing these compounds as a new class of PhotoCORMs. While the two 2,2'-bipyridine complexes release 1 equiv of CO per mole of complex, the terpyridine, 2-(2'-pyridyl)pyrimidine, and dipyrido[3,2-a:2',3'-c]phenazine complexes are less effective CO releasers. Attachment of the 2-(2'-pyridyl)pyrimidine complex to a PNA backbone as in [RuCl2(Cpp-L-PNA)CO2] did not significantly change the spectroscopic or CO-release properties compared to the parent complex. Thus, a novel class of Ru(II)-based PhotoCORMs has been established which can be coupled to carrier delivery vectors such as PNA to facilitate cellular uptake without loss of the inherent CORM properties of the parent compound.

Variation of the Photocurrent Spectra due to Energy Dependent Hole Mobility in Organic Bulk Hetero-junction Solar Cells

ABSTRACTA comparison of the photocurrent spectra of organic bulk heterojunction solar cells of various thicknesses is presented. Increasing the thickness of the active layer in both MDMO-PPV /PCBM and P3HT/PCBM solar cells reduces the magnitude of the photocurrent due to the low mobility of the photogenerated holes. Measurements show that the photocurrent reduction is predominately due to a loss in carriers generated at the polymer absorption maximum, while the low energy response is relatively unaffected. In a thick enough sample, the low energy response (1.5-2 eV) dominates, and a photocurrent peak is no longer observed at the main absorption maximum (2.6 eV). The results imply that hole transport is blocked for carriers generated in the polymer at higher energy. Because these holes are generated at the absorption maximum their low mobility could be a major factor limiting solar cell efficiency.

Pulsed-periodic UV emitter tunable near the main absorption maximum of a DNA molecule

The spectral characteristics of a pulsed-periodic lamp with three dielectric barriers are presented for the range 220–250 nm. As the active media of the lamp, krypton (Kr)-sulfur hexafluoride (SF6) and krypton-carbon tetrachloride (CCl4) mixtures are tested. The use of Kr-SF6 and Kr-CCl4 binary mixtures in two noncommunicating volumes is shown to be more effective than the use of a Kr-SF6-CCl4 ternary mixture with the same amount of Kr, SF6, and CCl4 constituents. The emission spectrum of the lamp near the maxima of the KrF(X-B) 248-nm and KrCl(X-B) 222-nm bands can be controlled by varying the partial pressures of halogen carriers and krypton.

Macromolecular physiology of plastids. XII. Tigrina mutants in barley: genetic, spectroscopic and structural characterization.

Several tigrina mutants of barley, namely tig-b7, -b19, -b23, -b24, -f11, -m31, -n32, -33, and -o34 can accumulate chlorophyll(ide) a (abbr. Chl a) with an absorption maximum near 742 nm in addition to Chl a absorbing near 676 nm. The amount of 742 nm absorbing Chl a present in mutant leaves is dependent on the allele and the growth conditions. The accumulation of 742 nm absorbing Chl a is accompanied by formation of abnormal membrane organizations in the plastids. Etiolated leaves of seedlings homozygous for mutations in the regulatory genes tig-b, tig-d, tig-n, tig-33, or tig-o accumulate protochlorophyll(ide) (Pchl) in amounts exceeding the wild type level. The final Pchl content is dependent on the particular mutant gene. Seedlings heterozygous for tig-b and tig-d mutations accumulate more Pchl than wild type seedlings. The increased Pchl contents are coupled with changed absorption properties of the etiolated leaves, the main absorption maximum in the red region being near 633 nm rather than near 650 nm. Abnormal membrane organizations are observed in etioplasts of the mutants tig-b7, -b19, -h23, -b24, -n32, -33, and -o34, while the ultrastructure of etioplasts of tig-d12 closely resembled that of the wild type. Membrane abnormalities in etioplasts are paralleled by altered carotenoid compositions in the mutants. Likewise, only those regulatory mutants with an aberrant carotenoid composition can accumulate 742 nm absorbing Chl a.

Emission characteristics of a discharge iodine vapor plasma in the spectral region of the main absorption maximum of DNA molecules

Radiation of glow and capacitive discharges in inert gas-iodine vapor mixtures is studied in the spectral range 150–210 nm, which coincides with the main absorption maximum of the DNA molecules. Iodine atomic spectral lines at 150.7, 161.8, 170.2, 183.0, and 206.2 nm are observed in the spectra. The emission intensity of the iodine spectral lines is optimized by varying the glow discharge current, capacitive discharge frequency, as well as pressure and composition of the gas mixtures. The glow and capacitive discharges are ignited in cylindrical quartz tubes with interelectrode gaps of 10 and 6 cm. Helium and neon are found to be the most effective buffer gases. The optimum partial pressures of the light inert gases and iodine vapor in the glow discharge are within 0.4–0.6 kPa and 100–150 Pa, respectively. In the capacitive discharge in He(Ne)-I2 mixtures, the optimum partial helium, neon, and iodine vapor pressures are within 0.8–2.0 kPa, 0.5–1.0 kPa, and ≤ 60 Pa, respectively. It is demonstrated that pulsed bactericidal radiation sources with light pulse lengths of 400–500 ns and continuous radiation sources emitting within the spectral range 150–207 nm can be designed on the basis of low-density iodine vapor plasma.

Mechanical spectroscopy of laser deposited polymers

Pulsed laser deposition (PLD) at 248 nm in ultra high vacuum was used to produce thin poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) films. The ablation and deposition mechanisms were found to be similar in both systems. Having the same backbone, these polymers differ in the size of their polar side groups leading to changes in their dynamics. Studies of the relaxation processes were performed using mechanical torsion and bending spectroscopy by means of a double-paddle oscillator (DPO) and an in-situ plasma plume excited reed (PPXR), respectively. A strong increase of the mechanical damping was observed during annealing of the polymer films well above the glass transition temperature T g, while in-situ X-ray measurements did not reveal any structural changes. For PEMA, the glass transition temperature T g=335 K and the main absorption maximum appear at lower temperatures compared to PMMA (T g=380 K), allowing one to measure the mechanical properties in a much wider range above T g.

XANES studies of thallium compounds and valence states and local environment of thallium in some of its superconducting cuprates

The position and shape of x-ray absorption discontinuities have been used to deduce structural and chemical bonding information on model compounds of thallium and its superconducting cuprates. The L x-ray absorption spectra were recorded on a Rigaku x-ray Spectrometer and monochromatized using a flat crystal of Si (1,1,1). The background subtraction was done using Victoreen function. The normalized absorption coefficient is plotted as a function of x-ray photon energy. It is observed that the XANES of LI edge has fewer features as compared to those of LIII edge. The LII edge spectra of thallium are similar to LIII edge spectra. The LIII absorption discontinuity of thallium splits into three components whereas no splitting is observed in LI edges. Thallium LIII edge spectra show a single absorption peak for monovalent compounds whereas in trivalent compounds a weak peak followed by a shoulder on rising absorption which culminates into a strong absorption peak. The important difference between the spectra of monovalent and trivalent compounds is the shift in the inflexion point energy of LIII edges and a shift of the main absorption maximum. The x-ray absorption spectra of superconducting cuprates show similarities with the spectra of Tl2O3 suggesting the presence of Tl3+ ions in octahedral configuration in these cuprates.

Interactions of Chlorophyll and Polypeptide Mixture with Bacterial Reaction Centres

In aqueous solutions of chlorophyll (Chl) a with synthesized polypeptides, at high ratios of Chl to polypeptides (about 75-150 µM to 500 µM) clusters of polypeptides and pigment molecules were formed. The main absorption maxima of more than one formed cluster were located at about 500 nm (Soret band) and in the region of 720-806 nm (red band). The formation of these clusters was fairly slow (some hours) at room temperature and even slower at 4 °C. The rate of cluster formation increased with the increase in Chl concentration. The addition of the even low amount of reaction centres (RCs), separated from the purple bacteria Rhodobacter sphaeroides, to the sample of Chl with polypeptides caused a very strong decrease in the efficiency of cluster formation, and a change in concentration ratios of various pigment-polypeptide aggregates. It was probably a competition between the interaction of Chl with polypeptides and with the RCs. The yield of thermal deactivation of the clusters was high, much higher than that for the RCs alone and it was different for various types of cluster. The clusters absorbing at 725-750 nm were fluorescent with maximum of emission at about 770 nm, whereas clusters absorbing at about 800 nm were nonfluorescent.

Substituted tetra-2,3-pyrazinoporphyrazines. Part II. Bis(tri-n-hexylsiloxy)silicon derivatives

Dichlorosilicon complexes of substituted tetra-2,3-pyrazinoporphyrazines were obtained via condensation of 2,3-dicyanopyrazine, 2,3-dicyano-5,6-diphenylpyrazine, 2,3-dicyanoquinoxaline, 2,3-dicyano-benzo[f]quinoxaline, and 2,3-dicyano-dibenzo[f,h]quinoxaline with silicon tetrachloride in the presence of urea, quinoline, and tri-n-butylamine. Hydrolysis of the Si-Cl bond in concentrated H2SO4, followed by treatment with 0.01 N NaOH and aqueous NH3, afforded the corresponding dihydroxides, which were converted to the bis(tri-n-hexylsiloxy)silicon derivatives via reaction with tri(n-hexyl)silane in 3-picoline (2,4,6-collidine) in the presence of tri-n-butylamine. The axial tri-n-hexylsiloxy substituents at the central silicon atom prevent aggregation in organic solvents, permitting detailed studies on the effects of structural modifications on the electronic spectra of tetraazaphthalocyanines. Our data show that each benzo ring addition, angularly condensed to the tetra-2,3-quinoxalinoporphyrazine, induces a hypsochromic shift (~ 10–15 nm) of the main absorption maximum. Key words: phthalocyanine, aza analog, bis(tri-n-hexylsiloxy)silicon complex.