V. A. Svetlichnyi

Photolysis of Phenol and para -Chlorophenol by UV Laser Excitation

The photolysis of phenol and para-chlorophenol by irradiation with the fourth harmonic of a neodymium laser was examined using electronic absorption spectroscopy, fluorescence, and quantum-chemical techniques. It was found that the introduction of a chlorine atom into the phenol molecule increases the efficiency of photolysis of para-chlorophenol by excitation in the long-wavelength absorption band. The O–H and C–Cl bonds in the test compounds are ruptured via a predissociation mechanism in triplet states localized at the breaking bonds.

Spectral and luminescent properties of some porphyrin compounds in different electronic states

The spectral and luminescent properties of some derivatives of tetraphenylporphyrin are studied at different concentrations of these compounds; the spectra of neutral and ionic forms are interpreted; and the quantum yields of ordinary and, in some cases, short-wavelength fluorescence from highly excited states are determined. The spectra of transient absorption from excited states, existing in the time range of tens of nanoseconds, are measured, and the quantum yields of formation of triplet molecules are estimated. Hypotheses regarding the mechanism of phototransformations of some porphyrins in chloroform are put forth.

Phototransformations of Phenols in Aqueous Solutions under Different Excitation Modes

The photolysis of aqueous solutions of two widespread environmental organic ecotoxicants—phenol and 4-chlorophenol—on excitation by UV radiation from a KrCl exciplex laser and a glow-discharge KrCl excilplex lamp was studied. The irradiated solutions were studied by spectroscopic techniques. The laser and lamp photolyses were compared.

Emission of Concentrated Solutions of Organic Compounds Excited with High-Power Laser Radiation

Specific features of emission of concentrated (C ≤ 1.2·1019 cm–3) solutions of organic molecules (rhodamine 6G, rhodamine C, phenalemine 512, and substituted paraterphenyl (LOC-1)) are investigated as functions of the exciting photon energy (at λexc = 308 and 532 nm) and power density of exciting radiation (up to 1 GW/cm2). One of the observed emission types – band emission – is studied. The intensity of band emission (its short- and long-wavelength maxima) is investigated versus the exciting radiation power density, and its time and polarization characteristics are also analyzed. The results obtained together with the specific features of the emission spectrum of concentrated rhodamine-C solution, measured after passage of sounding radiation with maximum at the wavelength equal to that of the short-wavelength maximum of band emission, demonstrate that the band emission is simply superfluorescence.

Phototransformations of Organic Compounds upon Powerful Laser Excitation under Nonlinear Absorption Conditions

Phototransformations, stationary- and induced-absorption spectra, and emission spectra of solutions of a dicarboxyalkyl derivative of p-terphenyl, as well as the transmission of exciting radiation from a XeCl laser by these solutions, were studied depending on the radiation intensity and degree of polarization. The reasons for variation in the quantum yield of phototransformations depending on the parameters of exciting radiation are discussed.

Spectroscopy of the excited-state complex of zinc(II) with 3,3′-bis(dipyrrolylmethene)

Spectra of nonstationary transient absorption of metal bis(dipyrrolylmethene) complexes in cyclohexane and ethanol, which exhibit different photophysical and photochemical properties in these solvents, have been measured and the yields of excited triplet states have been evaluated. It has been shown that the yield of triplets is determined by the intramolecular structure and the difference in fluorescence and phototransformation yields is due to intermolecular interaction of the excited molecules with the solvation shell.

Quantum-chemical study of relation of spectral and luminescent properties of positively solvatochromic malononitrile-based merocyanine dyes with their structure

The electronic structure, the spectra, and the efficiency of photophysical processes of energy deactivation are calculated by a semiempirical method for three positively solvatochromic merocyanine dyes with different polymethine chain lengths. The electronic structure and spectra calculated by different modifications of the INDO method at different molecular geometries are compared, and the optimum geometry of the isolated molecule is chosen. The absorption spectra of dyes are interpreted, including the short-wave-length bands related to transitions to highest excited states. The possibility of a specific electrophilic solvation of these compounds in the ground and fluorescent states, as well as the contribution of specific intermolecular interactions to the total interaction with the medium, is estimated. The role played by the trans-cis isomerization of isolated merocyanine molecules in the deactivation of their excited states is considered.

Specific Features of XeCl*-Laser Radiation Absorption by Concentrated Solutions of Organic Dyes

The transmission of focused laser radiation with power densities in the range (1–250) MW/cm2 through solutions of laser dyes (substituted paraterphenyls and rhodamine 6G) is investigated. The dependence of the transmission on the exciting radiation power density is measured, and numerical modeling is used to estimate the lifetime of the fluorescent state of molecules and the influence of stimulated emission on the lifetime of the S1 state. The effect of scattering on the transmission of highly absorbing media is demonstrated under nanosecond excitation.

Features of the electronic structure and photophysical processes in asymmetric and symmetric (dicyanomethylene)-pyran dyes

The electronic structure and photophysical processes in (dicyanomethylene)-pyran dyes, DCM and bis-DCM, have been studied by methods of quantum chemistry and optical spectroscopy. The spectral-luminescence and proton-acceptor properties for trans and cis conformers are investigated theoretically. The influence of the pyran ring geometry on the aforementioned properties and the efficiency of intramolecular photophysical processes in these molecules are analyzed. Simulation of trans-cis photoisomerization is performed, and its influence on the spectral-luminescence properties is studied.

Optical limiting and photoprocesses of new indotricarbocyanine dye

The results of experimental and theoretical studies into the optical characteristics of a new indotricarbocyanine dye are presented indicating that this dye shows much promise as an effective (nonlinear) power limiter for laser radiation in the visible. The luminescent and energy characteristics of the dye molecules are experimentally studied, and the absorption spectra are given with nanosecond resolution. The electronic absorption spectra for the ground (S0→Sn) and excited (S1→Sn) states are calculated using the quantum-chemical methods. A nature of the electronic state of the molecule under study is established, and a rate constant of the intramolecular processes is determined. The theoretical results coordinate well with the experimental data. The investigated dye reveals singlet-singlet absorption in the region 400-600 nm. Excitation of the dye is realized by the second harmonic radiation of a Nd-YAG laser. The Z-scan method with the open diaphragm is used to determine the absorption cross-section of indotricarbocyanine dye upon 532 nm excitation. The nonlinear absorption characteristics of the given molecule are compared to the earlier results obtained for other polymethine dyes.