S. M. Arabei

Spectral-luminescent properties and photoinduced transformations of bisanthene and bisanthenequinone

Based on the study of photochemical transformations of bisanthene in oxygen-containing solutions, it was established that the final product of this reaction is bisanthenequinone. It is shown that in the course of this oxidation reaction the intermediate compounds endomonoperoxide and bisanthene endobiperoxide are formed. Quantum-chemical calculation of the geometrical structure and electronic spectra of the endoperoxides has shown that they have a nonplanar structure, and their absorption spectra experience a large hypsochromic shift. The absorption and fluorescence spectra of solutions of bisanthene in different solvents at 300 and 77 K were investigated. The large Stokes shift of the fluorescence spectra of the solutions of bisanthene in benzene and in its methyl derivatives is explained by the action of intermolecular interactions. The quasi-line fluorescence spectra of solutions of bisanthene in the matrices of saturated hydrocarbons were recorded.

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.

Analysis of the Electronic Vibrational Spectra of Bisanthene by Calculating Normal Modes

At 4.2 K, the quasiline fluorescence and fluorescence-excitation spectra (in the region of the S1 ← S0- and S2 ← S0 transitions) of bisanthene in n-hexane have been obtained. Using the MO/M8ST method, the calculation of the Ag normal modes in the S0, S1, and S2 electronic states was carried out for the bisanthene molecule; the relative intensities of the transitions in the corresponding vibronic spectra were also calculated. The analysis of the results of calculations and experiment made it possible to draw conclusions on the form of the modes for a number of normal vibrations which are active in the bisanthene vibronic spectra.

The Influence of the Conditions of Sol–Gel Synthesis on the Absorption and Fluorescence Spectra of Porphyrin Molecules in Silicate Matrices

On the basis of the investigation of the electronic absorption and fluorescence spectra of porphin introduced into inorganic and organo–inorganic silicate gel matrices, the participation of the surface hydroxyl groups in the formation of the dication form of porphin is shown. The influence of the gel matrix drying process on the reverse process of deprotonation of the porphin dication has been revealed.

Fine‐Structure Fluorescence Spectrum of a Dication Form of Porphin in an Inorganic Gel Matrix

It is shown that the molecules of the free base of porphin (H2P) incorporated into an inorganic tetraethoxysilane (TEOS) gel matrix produce a dication form H4P2+. A fine‐structure spectrum of the fluorescence of H4P2+ is obtained at 4.2 K on selective photoexcitation. A conclusion on the manifestation of the out‐of‐plane vibrations of the porphyrin macrocycle in the low‐frequency region of the vibronic spectrum of porphin dication is drawn and the assignments of the corresponding frequencies to the vibrations of a certain form are suggested.

Photodestruction of Zinc Complexes of Tetrabenzoporphyrins in a Polymeric Matrix and Photosensitive Materials Based on Them

At room temperature, a high‐efficiency photochromogenic reaction of destruction of Zn‐tetra(4‐tert‐butylbenzo)porphin molecules in a polyvinylbutyral matrix has been revealed. The linear dependence of the photobleaching rate of porphyrin on the irradiation power density is indicative of a single‐photon character of the reaction. The influence of pyridine and ethyl iodide additives as well as of intermolecular oxygen on the photodissociation rate of pigment molecules has been investigated. The most probable mechanism of transformation of the porphyrin compound is its photodestruction involving free radicals. We suggest using the composition as a photosensitive material, and we have determined its photosensitivity experimentally (S = 0.4·103 cm2/J).

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.

Vibrational structure of quasiline fluorescence and absorption spectra of bisanthene molecules

AbstractThe quasiline spectra of the fluorescence and absorption of bisanthene in n-hexane are obtained at 77 and 4.2 K, and their vibration analysis is carried out. Substantial violation of the mirror symmetry of the fluorescence and S1 ← S0-absorption bands with respect to both the frequencies and intensities is found. This allowed the conclusion that the S2-level is localized in the region of vibronic sublevels of the S1-state with

Effect of the Electron-Vibrational Interaction on the Second Electron Transition of Tetraazaporphin and Tetraazachlorin Molecules

\Delta E_{S_2 S_1 } = 1395 cm^{ - 1}