K. N. Solov’ev

Interpretation of the soret band of porphyrins based on the polarization spectrum of N-methyltetraphenylporphin fluorescence

Low-temperature (77 K) absorption, fluorescence, and fluorescence-excitation spectra and the fluorescence polarization spectrum for N-methyl-meso-tetraphenylporphin (N-methyl-TPP) are measured. Based on the polarization spectrum the absorption spectrum in the visible region (a “generic” porphyrin spectrum) is interpreted. In particular, it is shown that the fifth absorption band (the “Longo band”) that manifests itself in some porphyrins is a Qy(0–2) band and does not belong to the individual electron transition. Emphasis is placed on the region of the Soret band. It is inferred that at least two allowed electron transitions (G →Bx and G→By) polarized mutually perpendicularly manifect themselves in this region. The interpretation of the Soret band of porphyrins [2] that attributes this band to one electron transition G→Bx is thereby rejected. This interpretation is confirmed by computer modeling of the polarization spectrum. Special features of the experimental polarization spectrum are explained by a more developed vibrational structure and, possibly, a larger half-width of the Bx band than the half-width of the By band. The contribution of the states of intramolecular charge transfer to the formation of the Soret band is discussed.

Spectroscopic and laser properties of photoexcited organic fluorescers embedded in composite gel systems

The spectral luminescence and lasing characteristics of rhodamine 101T and phenalemine 512 embedded in simple and composite gel matrices of different compositions based on tetraethoxysilane were excited by XeCl laser radiation and the second harmonic of a Nd:YAG laser. It is established that a dye interacts with a solid matrix through formation of donor-acceptor and hydrogen-bonded solvates. The dependence of the lasing efficiency on the excitation intensity was determined, as well as the laser photostability of gel systems with dyes. It is shown that the pump conversion efficiency and the laser photostability of dyes in composite gel systems are higher than in simple gel matrices.

Synthesis and spectral-luminescent properties of poly(N-isopropylacrylamide)

The spectral-luminescent characteristics of water and methanol solutions of polymers containing tetraphenylporphyrin substituents were investigated. The water-soluble polymer was obtained by the interaction of poly(N-isopropylamide) containing N-oxysuccinimide substituents with 5-(4-aminophenyl)-10,15,20-triphenylporphyrin. From the synthesized polymer its analog with Zn-porphyrin substituents was obtained. This phenomenon is attributed to the specific features of the conformational behavior of polymeric chains in water solutions. Water solutions of polymers experience a thermally reversible phase transition upon heating, which is accompanied by a considerable enhancement of light scattering.

Analysis of electronic vibration spectra of tetrabenzoporphin molecules on the basis of calculations of their normal vibrations

Quasi-line fluorescence and fluorescence-excitation spectra of tetrabenzoporphin (H2TBP) and its deuterated derivative (D2TBP) in n-octane at 77 K were measured and analyzed. A calculation of normal vibrations of the H2TBP and D2TBP molecules has been performed. The normal vibrations of these molecules were calculated with the use of the valence force fields of porphin and phenanthrene (the direct spectral problem was solved). Good agreement between the calculated and measured frequencies of the investigated normal vibrations has been obtained without correction of the transfered force constants. A detailed interpretation of the fluorescence spectra obtained is presented. It is shown that on deuteration of H2TBP, the behavior of the quasi-lines in the fluorescence-excitation spectra in the region of resonance with the S2←S0 transition becomes more complex.

SIMULATION OF THE DYNAMICS OF PHOTOBURNING OF STABLE SPECTRAL HOLES BY PULSED FREQUENCY-PERIODIC AND CONSTANT SOURCES

Based on the solution of a system of kinetic equations, computer simulation of the dynamics of laser radiation-induced burning of spectral holes is carried out to settle the question in which of the excited states photochemical NH-tautomerization occurs in free bases of porphyrins. A method is suggested to determine experimentally the electronic state in which a displacement of internal protons occurs that leads to the burning of a hole. The method is based on measuring the time dynamics of the formation of the hole. A new approach to determining the population of electronic levels in the process of molecular rearrangement on excitation by continuous lasers is described.

Quasiline fluorescence and absorption spectra of NH-isomers of octamethylisobacteriochlorin

Quasiline fluoresence and fluorescence excitation spectra of NH-isomers of 2,2,7,7,12,13,17,18-octamethylisobacteriochlorin (cis- and trans-) in polycrystalline matrices in n-hexane and n-octane at 4.2 K are obtained. A vibration analysis of the spectra in combination with the data of quasiline spectra of cyano-substituted octaethylisobacteriochlorin and octamethylporphin permitted a qualitative interpretation of the vibronic spectra of NH-isomers. It is inferred that for a trans-isomer, the 0–0 transition S2⇃S0 is localized in the region of electron-vibrational S1⇃S0 transitions; the interval S2-S1 has a magnitude of about 1300 cm−1.