Yu. P. Morozova

Influence of Solvents on the Spectral and Luminescent Properties of Phenol

The features of the absorption and fluorescence spectra of phenol in homogeneous and binary solvents have been investigated. The spectral characteristics of normal-hydrogen-bonded phenol–solvent complexes are compared to those of solvated anions. To explain the extinction of the fluorescence of the solvated anion, results of quantum-chemical calculations are involved.

Spectral and luminescent properties of chlorine-substituted derivatives of aniline

The effect of the position and number of chlorine atoms on spectral, geometrical, and photophysical characteristics of individual molecules of chlorine-substituted derivatives of aniline is studied by electronic spectroscopy and quantum-chemical calculations. It is shown that the long-wavelength absorption band of these compounds is formed by several electronic transitions of different nature and intensity. It is ascertained that electronically excited π σ* states involve C-Cl bonds, which weaken upon excitation. According to quantumchemical calculations, the quenching of fluorescence of chlorine-substituted derivatives of aniline is determined by the fact that intersystem crossing is more effective than radiative decay of the S1 state.

The Effect of Heteroatom Position on the Spectral-Luminescent Properties of Monochloroanilines

The effect of position of a heteroatom in the phenyl radical of aniline on the spectral, geometric, and photophysical characteristics of free molecules of monochloroaniles is studied by electron microscopy, fluorescence, and quantum chemistry. The position of energy levels of singlet and triplet states of monochloroanilines are found. It is shown that substitution by chlorine in aniline results in an increase in the singlet-triplet conversion and emergence of a new path of the internal conversion in the triplet-state system.

Intermolecular Interactions. Absorption and Fluorescence Spectra of α-Naphthol

In the ground state, α-naphthol interacts with water via oxygen, whereas with alcohols (ethanol and isopropanol) and acetonitrile it interacts via hydrogen from the hydroxyl group. In the excited state, α-naphthol interacts much more weakly. An analysis of the dependences of positions of electronic-vibrational transitions on the solvent basicity and acidity demonstrates their nonlinearity. For the parameters describing the solvation ability of the solvent, linear dependences are observed for the following series of solvents: isopropanol, ethanol, acetonitrile, and water. The possible values of the acid number (pA*) for the excited α-naphthol molecule fall within the interval from 0.4 to 1.4 depending on the chosen maximum of the absorption band. In fluorescence spectra, the band intensities differ for neutral and ionic modifications of the molecule. The fluorescence efficiency of the neutral molecule is by an order of magnitude higher than that of the ionic modification. Possible channels of quenching of the ionic modification are discussed.

INVESTIGATION OF THE HEAVY-ATOM EFFECT ON THE SPECTRAL-LUMINESCENT PROPERTIES OF DICHLOROANILINES

The influence of the chlorine atom position on the spectral, geometric, and photophysical characteristics of free molecules of dichloroaniline is studied by electron spectroscopy, fluorescence, and quantum chemistry. A chlorine atom included in the aniline aromatic ring is shown to exhibit properties inherent in a heavy atom, that is, the radiation is dominated by phosphorescence. According to quantum-chemical calculations, the quenching of fluorescence is due to the fact that the efficiency of the intersystem crossing conversion proves to be much higher than the radiative decay rate of the S1 state.

Intermolecular interactions of a para-nitroaniline molecule in binary solvents

The composition of the solvation sheath of a p-nitroaniline molecule in the ground state in mixed solvents (hexane+tetrachloromethane and hexane+isopropyl alcohol) is determined based on the dependence of the ππ*-absorption band shift on the composition of the binary solvent. The interaction of the nitro-group with isopropyl alcohol and water is considered based on results of calculations by the method of intermediate neglect of differential overlap (INDO) and experimental data. It is shown that when the hydrogen bond is formed, the lower singlet level corresponds to the ππ* state. Because of the high rate constant of intercombination conversion, only phosphorescence is characteristic of p-nitroaniline.

Quantum yields of oxazines and phenoxazines and the investigation of their spectral luminescence properties in binary mixtures

The electronic spectra of Nile Blue acetate, phenoxazines, and its fluorinated analogs have been investigated experimentally and theoretically. The spectral-luminescence properties of these molecules have been studied in detail in ethanol and in nonpolar solvents (toluyl, dimethylsulfoxide) with an alcohol admixture (propanol, butanol, and isobutyl alcohol). The role of micelle formation in non-aqueous solvent on the spectral-luminescence of these molecules is elucidated. Also considered in this paper is the dependence of the quantum fluorescence yield of several oxazines and phenoxazines in ethanol on the structure of the dye molecules.

Singlet-triplet transitions in substituted benzenes containing OH and NH2 groups

The electronic absorption spectra of substituted benzenes containing OH and NH2 groups are investigated in the 2500–5000 Å region. It is shown that the absorption band in the long-wave region is a singlet triplet absorption band.