V. Yu. Gak

Photochemical and photophysical properties ofmeso-tetraferrocenylporphyrin. Quenching ofmeso-tetraphenylporphyrin by ferrocene

It was found that the quantum yield of the fluorescence ofmeso-tetraferrocenylporphyrin (TFcP) is at most 3.0·10−5, and that of the triplet state of FTcP is at least 200 times lower than the quantum yield ofmeso-tetraphenylporphyrin (TPP). Excitation of TFcP in CCl4 by light with λ>410 nm results in the oxidation of TFcP. The singlet and triplet excited states of TPP in toluene and acetonitrile are quenched by ferrocene with rate constants of 1.2·1010 and 1.7·1010, (4.6±0.5)·108 and (1.37±0.21)·109 L mol−1 s−1, respectively. The quenching mechanisms are discussed.

Femtosecond relaxation of photoexcited states in nanosized semiconductor particles of iron oxides

Relaxation of photoexcited states in nanosized semiconductor particles of iron oxides was studied by femtosecond laser photolysis techniques: (1) in an aqueous colloidal solution of α-Fe2O3; (2) in Fe2O3 particles in the Nafion® cation-exchange polymeric membrane; (3) in an aqueous colloid of γ-Fe2O3; and (4) in nanocrystals of ferrihydrite 5Fe2O3·9H2O, which are contained in the protein shell of ferritine. The photoinduced excited states relax at the femtosecond and picosecond time scale. The spectra of photoinduced absorption of photoexcited states and the relaxation dynamics in the studied iron oxides weakly depend on the structure and surface environment of a nanoparticle.

On the possibility of nonradiative energy transfer between hydrophobic quantum dots in solutions

The Förster resonance energy transfer between CdSe quantum dots with two different sizes has been studied in an organic solvent upon the formation of close-packed aggregates of quantum dots, with the aggregation being both spontaneous and induced by a precipitating solvent. The addition of a precipitant has been established to noticeably increase the efficiency of the energy transfer. It has been shown that the sizes and numbers of resulting aggregates may be controlled by varying the experimental conditions.

Spectral-Luminescent properties of the dioxytetramethylene-bridged naphthol-styrylquinoline dyad

The spectral-luminescent properties of the naphthol-styrylquinoline dyad 2-(E)-{4-[4-(3-hydroxynaphthalen-2-yloxybutoxy]styryl}quinoline (SQ4Np) have been investigated. Fluorescence quenching of the naphthol (Np) moiety via energy transfer to the styrylquinoline (SQ) moiety has been observed upon dyad excitation. A comparison of stationary and time-resolved fluorescent spectroscopy data has revealed two groups of conformers, for which the energy-transfer rate constants differ by more than two orders of magnitude. According to quantum-chemical calculations (B3LYP/6-31G* method), the s-cis-conformation of the SQ fragment is the most stable SQ4Np conformer with the all-trans-conformation of the dioxytetramethylene bridge and intramolecular hydrogen bond in the Np moiety; the van der Waals size of this conformer is 2.90 nm, which is less than the calculated Forster radius of R0 = 3.8 nm.

Colloidal quantum dots InP@ZnS: Inhomogeneous broadening and distribution of luminescence lifetimes

Indium phosphide colloidal quantum dots with a zinc sulfide shell, an average core diameter of 3 nm, a luminescence peak position of 600 nm, and a luminescence quantum yield up to 50% have been synthesized. By analyzing the stationary absorption and luminescence spectra in terms of the Kennard—Stepanov relationship, the values of homogeneous width and inhomogeneous broadening have been obtained, which determine the resulting width of the spectra: the corresponding full widths at half maximum (FWHM) were 31, 63, and 70 nm. From the value of inhomogeneous broadening and the sizing curve of indium phosphide, polydispersity of the synthesized particles has been estimated as 11%. Analysis of the luminescence decay kinetics has revealed three reproducible peaks with maxima near 4.35, 35 (main) and 200 ns in the lifetime distribution. It has been found that although repeated washing of the synthesized particles with methanol can decrease the quantum yield, the lifetime distribution observed remains constant, which in the context of the “blinking” effect indicates a very short luminescence decay time of the particles in the OFF-state.

Effect of the solvent composition in methanol-pentane and methanol-acetonitrile mixtures on the spectral and luminescent properties of 1,2-dihydroquinolines

The dependence of absorption and fluorescence spectra, quantum yields, and lifetimes of fluorescence on the solvent composition in the MeOH-C5H12 and MeOH-MeCN mixtures was studied for 2,2,4,6-tetramethyl-1,2-dihydroquinoline (TMDHQ). The variations in the parameters of deconvolution of the absorption and fluorescence spectra by the Gaussian functions in the MeOH-C5H12 mixtures of various compositions indicate the specificity of methanol clustering in saturated hydrocarbons and hydrogen bonding between TMDHQ and the methanol clusters of different compositions. At low MeOH concentrations (∼0.2 vol %), TMDHQ molecules are practically completely bound with the MeOH molecules by hydrogen bonds. In the MeOH-MeCN mixtures, the changes in the absorption and fluorescence spectra are observed at a substantially higher MeOH concentration (≥10 vol %) and monotonically change at the further increase in the MeOH concentration that is caused by the peculiarities of MeOH clustering in acetonitrile and the distribution of the TMDHQ molecules between the solvent components. At 50–95 vol % of MeOH in the mixture with MeCN, the fluorescence decay kinetics is described by the biexponential curve with the lifetime of the major component (τ1) decreasing from 7.5 to 1.1 ns in pure MeCN and MeOH, respectively, and the lifetime of the minor component τ2 ≈ 4 ns corresponding to the fluorescence lifetime in the solution containing 50 vol % MeOH. This indicates the existence of the free TMDHQ molecules, which are not bound with MeOH molecules or their clusters.

Magnesium octa[(4′-benzo-15-crown-5)oxy]phthalocyaninate in water micellar solutions of sodium deoxycholate

Aggregation of magnesium octa-[(4′-benzo-15-crown-5)oxy]phthalocyaninate (Mgcr8Pc) in solutions of biocompatible anionic surfactant, sodium deoxycholate (SDC), was studied. It was shown using the electron absorption spectra that formation of Mgcr8Pc monomers in micellar solutions of SDC is affected by both increased surfactant concentration and by changes in the ionic strength of solution after sodium chloride is added. The effect of the chemical structure of biocompatible anionic surfactant on monomerization of crown-containing phthalocyanines was identified; this fact opens new possibilities for using this family of compounds for fluorescent diagnosis and photodynamic therapy.

Spectroluminescent properties of cadmium selenide nanoparticles synthesized in AOT reverse micelles

Cadmium selenide nanoparticles have been synthesized in solutions of AOT/water/n-heptane reverse micelles with average micelle water pool diameters of 25, 30, and 47 Å using cadmium sulfate (CdSO4) and sodium selenosulfate (Na2SeSO3) as precursors. Absorption and fluorescence spectra of the obtained nanoparticles were recorded. The picosecond dynamics of fluorescence decay over the entire range of their emission band have been investigated by time-resolved fluorescence spectroscopy. A procedure for the stabilization of nanoparticles by dodecanethiol was developed for electron microscopy analysis.

Preparation and Properties of Hybrid Nanostructures of Zinc Tetraphenylporphyrinate and an Amphiphilic Copolymer of N-Vinylpyrrolidone in a Neutral Aqueous Buffer Solution

Water-soluble forms of a hydrophobic dye, zinc tetraphenylporphyrinate, are obtained via its solubilization by polymer particles of the micellar type formed by a copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate. Hydrodynamic radii Rh and the size distribution of such particles in neutral aqueous buffer solutions are determined via dynamic light scattering. The electrochemical activity of the encapsulated dye is found, and its photochemical properties (absorption and fluorescence) are studied.

Influence of alkanethiols on fluorescence blinking of InP@ZnS colloidal quantum dots

Luminescence decay curves have been measured for InP@ZnS colloidal quantum dots (CQDs) synthesized at different ratios between 1-octanethiol and 1-dodecanethiol. The luminescence lifetime distributions reflecting the ratios between the on, off, and grey states of CQDs have been calculated. With an increase in the portion of 1-octanethiol, the distribution is shifted toward the on states, which almost completely suppresses fluorescence blinking at all detection wavelengths.