Study of the complexation and solvation of polar molecules in binary solvents by differential spectroscopy

A method of application of differential absorption spectroscopy for determining the absorption spectra of primary 1: 1 solvated complexes between polar molecules of an organic dye and the active component of a binary solvent whose neutral component is a nonpolar liquid is proposed. The method was tested on diluted solutions of 4-dimethylaminochalcone (4-DMC) (which is one of the most efficient spectral-luminescent probes used in present-day medical and biological investigations) in mixtures of n-hexane with acetone at extremely small concentrations of the polar component. It is shown that the experimentally found absolute shift of the long-wavelength absorption band of 4-DMC is in satisfactory quantitative agreement with the analogous value obtained independently on the basis of the theory describing the joint effect of nonlinear (complexation) and linear (solvation) dipole-dipole interactions on the spectral band positions.     

Selective nonspecific solvation under dielectric saturation and fluorescence spectra of dye solutions in binary solvents

The influence of selective nonspecific solvation on the fluorescence spectra of three substitutedN-methylphthalimides in a binary solvent system consisting of a nonpolar (n-heptane) and a polar (pyridine) component has been studied under conditions close to dielectric saturation. The substantially nonlinearity of the effect is confirmation that the spectral shifts of fluorescence bands depend on the number of polar solvent molecules involved in solvating the dye molecule. The measured fluorescence spectral shifts determined by substituting one nonpolar solvent molecula with a polar one in the proximity of the dye molecule agree quantitatively with the forecasts of the previously proposed semiempirical theory which describes this nonlinear solvation phenomenon.     

Effect of solvation on polarization characteristics of fluorescence for 1,3,4-oxadiazole derivatives in binary solvents

We have studied the degree of fluorescence polarization for 1,3,4-oxadiazole derivatives in the binary solvents hexane-ethanol, toluene-ethanol, toluene-acetonitrile, 2-propanol-water, dioxane-water, 2-propanol-glycerol, glycerol-water vs. the composition of the solvent. We have shown that in systems with predominant universal interactions, the characteristic changes in the degree of polarization reflect the change in the viscosity of the mixture, while in systems with pronounced specific interactions they reflect the characteristic structural features of the fluorescent centers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 677–683, September–October, 2008.     

Temperature effects on the fluorescence of indolic molecules in polar solvents. Anomalous stokes shift

The fluorescence Stokes shift of polar solutions of indole is explained on the basis of the interaction of solute-solvent hydrogen-bonded complexes with their polar cages. Temperature dependence of N-methylindole versus indole fluorescence is used in this study.     

Optical and spectral properties of associated molecules of rutin and γ-formylmesoporphyrin in binary mixtures of polar solvents

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 2, pp. 270–274, August, 1991.     

Extreme narrowing of bands in the fluorescence excitation spectra of organic molecules in solid solutions

Extreme narrowing of bands in the fluorescence excitation spectra of some organic molecules is found. This narrowing is observed when the excitation spectrum of a narrow spectral interval of the fluorescence band is recorded. The effect is observed in a wide variety of matrices and permits one to determine exactly the vibronic structure of the excited electronic state of the dissolved molecule.     

Formation of fluorescence bands of polyatomic organic molecules in the gaseous phase upon excitation by electrons

Information on paths in absorption and deactivation of energy gained by molecules in their excitation by electron impact to low-lying singlet states has been obtained from an analysis of changes in the fluorescence spectra of these molecules. It is shown that there is a significant difference in the formation of fluorescence spectra when free molecules are excited by optical radiation and by electrons. It contrast to optical excitation, the interaction of an electron with a molecule is nonselective in character. All electronic states have a chance to be excited, which results in ensembles of emitting molecules with a different store of vibrational energy, and these ensembles each contribute to the fluorescence spectrum. Deceased. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 216–223, March–April, 1998.     

Quenching of fluorescence for fluoro derivatives of the laser dye DCM in polar solutions

We used fluorescence spectroscopy and nanosecond flash photolysis to study the photophysical properties of the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylamino)styryl-4H-pyran (DCM) and its two fluoro derivatives: (E)-2-〈2-[2-(4-dimethylaminophenyl)ethenyl]-6-trifluoromethyl-4H-4-pyranylidene〉malononitrile (DCMF3) and (E)-2-〈2-[2-(4-dimethylaminophenyl)ethenyl]-6-n-heptafluoro-propyl-4H-4-pyranylidene〉 malononitrile (DCMF7), in nonpolar n-hexane, mixtures of low-polarity toluene and polar dimethylsulfoxide (DMSO), n-propanol at room temperature and at 77 K. The fluorescence quantum yield Φ_fl of the laser dye DCM increases linearly as the polarity of the binary solvent mixture (toluene+DMSO) increases, from 0.08 in toluene to 0.80 in DMSO. The dependence of Φ_fl on the polarity of the mixture toluene+DMSO for DCMF3 and DCMF7 reaches a maximum for a small amount (∼2 vol.%) of added polar DMSO; and with further increase in the DMSO concentration (≥50 vol.%), the fluorescence of the fluoro derivatives of DCM is practically completely quenched. The quantum yield for intersystem crossing Φ_ST for DCM, DCMF3, and DCMF7 is no greater than 0.01 in solutions of different polarities. We discuss the mechanisms for nonradiative deactivation of the electronic excitation energy for the fluoro derivatives compared with DCM. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 606–612, September–October, 2006.     

Using localized surface plasmons to modify the optical properties and conformational rearrangements of organic dye molecules

Optical properties of the molecular layers of cyanine dyes and their modification in a nearby field of silver nanoparticles on a sapphire substrate are investigated experimentally. Enhancement of the fluorescence and absorption intensity of organic molecules in the presence of silver nanoparticles is observed. The results from photomodifications of the molecular layers’ absorption properties with and without the presence of silver nanoparticles are described.