K. N. Solovyov

Anisotropy of Light Emission and Absorption by Porphin Molecules in n-Octane Single Crystals

Abstract Detailed information on vibrational structure of electronic transitions in molecules is necessary for the elucidation of the properties of excited electronic states, for the understanding of characteristics of polarized luminescence, circular dichroism and magnetic circular dichroism, sometimes also for solving problems of vibrational spectroscopy. The Shpolsky method of quasi-line spectraI makes it possible to obtain data on frequencies of vibrations and their activity in vibronic spectra of fluorescence and absorption. In principle, the method enables also determination of polarization of separate vibronic transitions, but monocrystalline samples are necessary for this purpose. The first investigations of quasiline spectra of monocrystalline samples (stilbene in n-octane) were carried out by Malykhina and Shpak2.

Manifestation of the vibronic analogue of the Fermi resonance in quasi-line spectra of porphyrins: Experiment and theoretical analysis

The quasi-line low-temperature (4.2 K) fluorescence excitation spectra of two porphyrins, meso-tetraazaporphin and meso-tetrapropylporphin introduced into an n-octane matrix are measured in the range of the S0 → S2 electronic transition. A characteristic feature of these spectra is that a conglomerate of quasi-lines—a structured complex band—is observed instead of one 0–0 quasi-line of the S0 → S2 transition. In this band, the intensity distributions for the two main types of impurity centers considerably differ from each other. The occurrence of such conglomerates is interpreted as a result of nonadiabatic electronic-vibrational interactions between vibronic S2 and S1 states (the complex vibronic analogue of the Fermi resonance). The frequencies and intensities of individual transitions determined from the deconvolution of complex conglomerates are used as the initial data for solving the inverse spectroscopic problem: the determination of the unperturbed electronic and vibrational levels of states involved in the resonance and the electronic-vibrational interaction matrix elements between them. This problem is solved with a method developed previously. The energy intervals between the S2 and S1 electronic levels of the two main types of impurity centers formed by molecules of a given porphyrin in the crystal matrix are found to significantly differ from each other (∼100 cm−1). At the same time, the energies of the unperturbed vibrational states of the S1 electronic level partcipating in the resonance are very close to each other for these two types of impurity centers.

Spectroscopic and laser characteristics of new efficient luminophores for a wide spectral range based on complexes of dipyrrolylmethene derivatives with difluorine borate

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.

IR SPECTRA OF Zn PHTHALOCYANINE AND Zn PHTHALOCYANINE-d 16 AND THEIR INTERPRETATION ON THE BASIS OF NORMAL COORDINATE ANALYSIS

IR spectrum of perdeuterated Zn phthalocyanine (ZnPc-d 16) has been obtained and compared to that of non-deuterated ZnPc. For both cases normal coordinate analysis has been carried out, and the isotopic shifts on deuteration have been satisfactorily described. The form of the in-plane modes of the Eu symmetry type has been characterized by potential energy distribution.

Phenyl substituted Mg porphyrazines: The effect of annulation of a chalcogen-containing heterocycle on the spectral-luminescent properties

We have performed complex experimental and theoretical investigations of the spectral-luminescent properties and electronic structure of new phthalocyanine analogs, Mg octaphenylporphyrazine and its derivatives with an annulated thiadiazole or selenadiazole ring instead of two phenyl groups. Fluorescence characteristics have been determined at 293 and 77 K: emission, excitation, and fluorescence polarization spectra; fluorescence quantum yield φF, and lifetime τF. Annulation of a five-membered chalcogen-containing heterocycle leads to splitting of the long-wavelength absorption band Q(0-0) and to the bathochromic shift of its longest wavelength component Qx(0-0), which increase upon passage from S to Se. At the same time, the fluorescence quantum yield φF and lifetime τF decrease, which is related to the intramolecular heavy-atom effect. The geometric structure of the ground state of the Mg porphyrazine molecules has been determined based on the density functional theory (DFT), and excited electronic states have been calculated with modified parametrization of the INDO/S method, INDO/Sm. Semiquantitatively, the calculated level positions of the lowest Q states and spectral shifts of Mg octaphenylporphyrazine and S-derivative agree with experimental data. For the range of the Soret band, calculated transition energies and their intensity distributions substantially depend on the dihedral angle γ between a phenyl ring and porphyrazine macrocycle. We show that, based on calculations at the angle γ = 60°, bands in the observed absorption spectra can be assigned with an accuracy of ∼2000 cm−1.

Study of Vibronic Spectra of Tetrabenzoporphin Based on Normal-Coordinate Analysis

Abstract The quasi-line fluorescence spectra have been measured and analyzed in detail for the molecules of tetrabenzoporphin and its N-deuterated derivative in n-octane. The calculations of the normal modes of these molecules have been carried out with the use of the valence force fields of porphin and phenanthrene. Sufficiently good agreement of the calculated and experimental frequencies of the modes has been obtained without variation of the force constants. Detailed interpretation of the fluorescence spectra is given.

The fluorescence and electronic structure of phenyl-substituted tetraazachlorin molecules

The effect of the addition of phenyl groups to pyrrole rings of tetraazachlorins, a new class of tetrapyrroles, on the photophysical properties and electronic structure of the molecules has been investigated by a complex of experimental and theoretical methods. Characteristics of fluorescence at 293 and 77 K have been determined for phenyl-substituted tetraazachlorins. The objects of this study include unsubstituted tetraazaporphine. The introduction of phenyl groups affords a marked increase in the fluorescence quantum yield. For tetraazaporphine and phenyl-substituted tetraazachlorins, fluorescence buildup occurs as the temperature is decreased from 293 to 77 K, but to a lesser extent than for tetraazachlorins having no phenyl groups, which were earlier studied by the authors. The fluorescence buildup mechanism is discussed. The singlet oxygen generation quantum yield has been determined for the tetrapyrroles examined. This characteristic increases upon tetrapyrrole is phenylation. The electronic structure and absorption spectra of unsubstituted porphine and chlorin, tetraazaporphine, tetraazachlorin, octaphenyltetraazaporphine, and tetramethylhexaphenyltetraazachlorin have been calculated by the INDO/Sm method (original modification of the INDO/S method) with molecular geometry optimization using DFT. The results of the quantum-chemical calculation of the absorption spectra are in good agreement with experimental data for transitions to the lowest excited electronic states Qx(S1) and Qy(S2).

Novel porphyrin-labelled poly(N-isopropylacrylamides): syntheses from bromoalkyl-containing prepolymers and physicochemical properties

Novel water-soluble tetraarylporphyrin-labelled polymers have been synthesized by the reaction of bromoalkyl-containing poly(N-isopropylacrylamides) with 5-(4-pyridyl)-10,15,20-tri(4-methoxyphenyl) porphyrin. Corresponding Zn-porphyrin-containing polymers have also been prepared. Phase transition diagrams show that aqueous polymer solutions exhibit phase separation upon heating. Absorption spectra of the porphyrin-labelled polymers have been recorded in water and organic solvents. It is found that the absorption bands in aqueous polymer solutions are broadened and shifted bathochromically, the peak intensity of the Soret band in the polymer spectra being strongly lowered in water. Fluorescence properties of the polymers are briefly reported.

Optical and physico-chemical properties of tetrapyrrole molecules in nanoporous silicate gel matrices

In this mini-review, we present the main results of our works on the spectroscopy of the molecules of tetrapyrrole pigments incorporated into nanoporous gel matrices. Xerogels activated by organic dyes are promising materials for applications in various fields of technology. The influence of the technique of embedment of the activator molecules on their physico-chemical properties has been analyzed. The specificity of the action of a silicate matrix as external medium, as compared to liquid and solid solutions, is shown.

Spectral, luminescent, and lasing characteristics of pyridyloxazole derivatives in inorganic and hybrid gel materials

The spectral, luminescent, lasing, and photochemical characteristics of two pyridyloxazole derivatives incorporated during the sol-gel synthesis into inorganic silicate and hybrid organic-inorganic xerogels in the form of bulk matrices and thin films are studied. It is found that organic molecules are fixed in nanopores of solid matrices by specific interactions between proton-accepting centers of molecules and proton-donating centers of silicate matrices and create cationic and dicationic forms under such interactions. It is shown that pyridyloxazoles are more photostable in solid xerogels than in solutions.