V. Ya. Artyukhov

Electronic structure, spectral-luminescent, and proton acceptor properties of biologically active aminophenols

The absorption and fluorescence spectra and fluorescence quantum yields of a number of biologically active derivatives of o-aminophenol are measured in an inert solvent, hexane. The IR spectrum of a solution of 2-amino-4,6-di-tert-butylphenol is studied in CCI4 and IR bands are found that indicate the presence of two conformers in this solution with intramolecular hydrogen bonds O-H…N and N-H…O. Using methods of IR Fourier transform spectroscopy, the structural features of a number of biologically active o-aminophenols with different substituents are considered. The absorption and fluorescence spectra of o-aminophenols are calculated and interpreted by the method of intermediate neglect of differential overlap with spectroscopic parameterization. Calculation data are compared with the results of the experiment. Proton acceptor properties of o-aminophenol molecules are theoretically evaluated using the method of molecular electrostatic potential. The role played by various substituents in the formation of the proton acceptor properties of o-aminophenols is experimentally studied.

Experimental and Theoretical Investigation of the Spectral and Luminescent Properties of Some Acridine Compounds

Complex (experimental and quantum-chemical) investigation of the spectral and luminescent properties of acridine, 9-aminoacridine, 2,7-dimethyl-9-ditolylaminoacridine, and their protonated forms was performed. The electronic absorption and fluorescence spectra of the acridine dyes were studied at room temperature in ethanolic solutions at different pH values and in other solvents of different chemical nature and polarity. The energies of the excited states, the deactivation rate constants for the excited states, and the dipole moments are presented, which were obtained by calculations using the method of intermediate neglect of the differential overlap with special spectroscopic parameterization.

Spectroscopic parametrization of the method of PNDO

Special spectroscopic parameterization of the semiempirical PNDO method for calculating the spectral characteristics of polyatomic heterocyclic molecules is proposed. The parameters are calibrated according to the experimental absorption spectra, photoelectronic spectra, and the dipole moments of benzene and its derivatives.

Three-center integrals of one-electron operator of a spin-orbit interaction

A computational algorithm for three-center integrals in matrix elements of a spin-orbit interaction operator is developed. The explicit form of the integrals is derived. Empirical and calculated atomic constants of the spin-orbit interaction are compared. The effect of interatomic spacing in the atom chain on the magnitude of integrals is considered. Distinctions between one-center and multicenter approximations as well as the range of application are analyzed using planar and nonplanar compounds as examples.

Quantum-Chemical Study of the Effect of Chlorine Substitution on Spectral and Luminescent Properties and Photolysis of Phenol and Its Complexes with Water

The effect of chlorine substitution on the spectral and luminescent properties and photolysis of phenol and its 1 : 1, 1 : 2, and 1 : 3 complexes with water was studied by quantum chemistry methods. The chlorine substitution in the para position of phenol was found to decrease the fluorescence quantum yield and to make it dependent on excitation energy in the absence of phototransformations. The nature of photodissociative states and a mechanism for the photocleavage of O–H and C–Cl bonds in p-chlorophenol were determined.

Electronic structure and spectroscopic properties of anti-HIV active aminophenols

We have measured the absorption and fluorescence spectra and fluorescence quantum yields of sulphone-containing anti-HIV active o-aminophenol molecules in an inert solvent, hexane, and in a polar solvent, acetonitrile. We have studied IR Fourier-transform spectra and examined structural features of o-aminophenols with different substituents in solutions and crystals. Functional groups of molecules that are involved in the formation of hydrogen bonds have been revealed. Proton acceptor properties of o-aminophenol molecules have been theoretically evaluated using the method of molecular electrostatic potential. Using quantum chemistry methods, we have calculated and interpreted absorption and fluorescence spectra of o-aminophenols. Calculation data are compared with experimental results. We have determined the main channels and mechanisms of photophysical relaxation processes in o-aminophenols.

Nature of the electron-excited states and the mechanism of nonradiative energy transfer in aromatic bifluorophores

Quantum-chemical calculations have been carried out for molecules of the bifluorophores naphthalene-(CH2)n-anthracene. The electronic structure and molecular-orbital nature of the excited electronic states of the molecules was analyzed and the rate constants of the photophysical processes were estimated. It is shown that for molecules with n=1, 2, 3 the transfer of excitation energy from the donor fragment (naphthalene) to the acceptor (anthracene) is completely equivalent to internal conversion.

Photophysics of the analogs of pyrromethene PM 567

The spectral and luminescence properties of a number of pyrromethene (PM) dyes have been investigated. The absorption and luminescence spectra of PM molecules in different solvents are measured. The electronic structure and electronic excited states are calculated by the method of intermediate neglect of differential overlap with special spectroscopic parameterization. The rate constants of photophysical processes are estimated, and the fluorescence quantum yields are calculated. The fluorescence quantum yields of PM I and PM II molecules are found to decrease upon their excitation to the second short-wavelength absorption band. This phenomenon is interpreted.

Electronic structure and intramolecular photophysical processes of cations of symmetric indopolycarbocyanine dyes

The electronic structure, spectra, and rate constants of radiative and nonradiative processes of cations of the vinylogous series of symmetric indopolycarbocyanine dyes are calculated by the semiempirical method of partial neglect of differential overlap. The S0 → Sn absorption spectra are interpreted. The dependences of the efficiency of the deactivation of the fluorescent state on the length of the polymethine chain of cations are analyzed. The quantum yields of the fluorescence from the first and second singlet states are calculated. The calculation results agree satisfactorily with experimental data.

Specific features of the two-photon absorption of cationic symmetric polymethine dyes

The two-photon absorption of a number of cationic symmetric polymethine dyes based on 3H-indolium and benzothiazolium is experimentally studied upon excitation by nanosecond radiation from a Nd:YAG laser (1064 nm, 12 ns). The two-photon absorption cross section of dye molecules is determined by the two-quantum standard method. The influence of the spectral-luminescent properties and structure of the polymethine dyes on the two-photon absorption cross section is discussed. It is shown that, upon excitation in the range of the long-wavelength band of the dyes studied (the S0 → S1 transition), the maximum of their two-photon absorption is blue shifted. The reasons for a considerable increase in the two-photon absorption of symmetric polymethine dyes upon their excitation in the range of the S2 state are discussed. Using the data of quantum-chemical calculations, it is shown that, along with changes in the selection rules for two-photon transitions, this increase is connected with an increase in the size of the delocalized π electron cloud of HOMOs involved in the S0 → S2 transition.