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The electrophotophysical characteristics of laboratory samples of IR photodetectors obtained by dip coating of PbS colloidal quantum dots with the subsequent exchange of oleic acid molecules that compose their ligand shell by S2− ions have been studied.

The influence of 1,6-hexanedithiol as an additional short-chain stabilizing ligand on fluorescence blinking of semiconductor colloidal quantum dots InP@ZnS has been studied using the analysis of the fluorescence decay curves. The optimum proportion of 1,6-hexanedithiol in the mixture has been determined. The influence of the thickness of the ZnS shells and the diameter of the InP core has been also studied. Correlation of these dependences with the analogous dependences for the luminescence quantum yield is observed.

The behavior of crown- and phosphoryl-containing magnesium and zinc phthalocyaninates in solutions of synthetic and natural surfactants is studied. In a phosphate buffer (рН 7.4), zinc phthalocyaninate bearing oxy(pentyloxy)phosphoryl groups in peripheral substituents of the macrocycle is in aggregated state. According to absorption and fluorescence spectroscopy data, adding oppositely charged synthetic and natural surfactants leads to monomerization of this compound. The degree of monomerization of magnesium octa[(4´-benzo-15-crown-5)oxy]-phthalocyaninate in a microheterogeneous medium is affected by the concentration of sodium cholate and ionic strength. Fluorescence-active supramolecular gels based on sodium deoxycholate were prepared using phosphoryl-containing zinc phthalocyaninate.

Methods of absorption and fluorescence spectroscopy and, in some cases, small angle X-ray scattering, are used to study solubilization and supramolecular organization of octa[(4'-benzo-15-crown-5)-oxy]phthalocyanines (Pc), H2cr8Pc, and Mgcr8Pc in an aqueous medium in the presence of polyelectrolytes, sodium polystyrene sulfonate, and sodium carboxymethyl cellulose or their mixtures with anionic surfactants: sodium dodecyl benzene sulfonate and sodium deoxycholate. The obtained results indicate the appearance of a monomeric, fluorescent state of Mgc8Pc in the presence of sodium polystyrene sulfonate and at the further increase in its concentration with an increase in the solution ionic strength and addition of anionic sodium deoxycholate. In all cases, the monomeric state of Mgcr8Pc is confirmed by the data of fluorescence spectroscopy. Photobleaching of Mgcr8Pc solubilized in the monomer form is observed in aqueous micellar solutions of sodium dodecylsulfate and sodium dodecyl benzene sulfonate. In the presence of PSS/NaCl, aqueous solutions of Mgcr8Pc were also studied using dynamic light scattering and small-angle X-ray scattering.

Adsorption of meso-tetra(3-pyridyl)porphyrin (TPyP) on InP@ZnS colloidal quantum dots (QDs) has been studied by fluorescence spectroscopy. It has been found that after addition of TPyP to a solution of InP@ZnS QDs, the processes of growth of the TPyP photoluminescence intensity and quenching of InP@ZnS QD photoluminescence occur. The kinetics of these processes in the time range from a few seconds to tens of hours is logarithmic, which indicates a dispersion of the activation energy of the dye adsorption. The increase in the photoluminescence intensity of TPyP upon the adsorption is due to Forster resonance energy transfer. The adsorption of TPyP leads to small changes in its spectral characteristics and luminescence lifetime.

Spectral and photochemical properties of a bichromophoric dyad with two photochromes, 2-[(2-(pyren-1-yl)ethenyl]quinoline (PEQ) bridged by ten methylene groups have been investigated. Stationary spectroscopy does not show substantial interaction between the PEQ groups in the dyad, but the appearance of another, more long-living component in the f luorescence decay kinetics indicates possible excimer formation. The formation of the chemically active excimer is also confirmed by the intramolecular [2+2] photocycloaddition reaction to give tetrasubstituted cyclobutane with two vicinal pyrene substituents. This reaction competes with trans–cis photoisomerization of the dyad. It has been proposed that the π-stacking interaction of two PEQ groups with a long system of π-bonds plays an important role in the excimer formation followed by the photocycloaddition reaction.

This work is dedicated to low-molecular hydrogels based on biodegradable sodium deoxycholate (SDC) and lysine hydrochloride (lys × HCl) with magnesium octa-[(4'-benzo-15-crown-5)-oxy]phthalocyaninate (Mgcr8Pc) as the active component, namely, their synthesis, spectral properties of gel-solubilized Mgcr8Pc, its release from the gel etc. Addition of Mgcr8Pc occurs both via the mixing of the components and via its diffusion from the aqueous solution into the phase of the formed SDC/lys × HCl gel. Mgcr8Pc-containing hydrogels are thermoreversible. The state of Mgcr8Pc in the SDC/lys × HCl/NaCl gel at the room temperature and in the melt is studied using spectral methods. Gel melting releases Mgcr8Pc in the form of a micelle-bound monomer. The presence of the Mgcr8Pc monomer phase in the phthalocyanine-carrying supramolecular hydrogel causes fluorescent activity of the latter.

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.

Spectral, luminescent, and kinetic characteristics of nanoclusters of hydrophobic colloidal quantum dots (CQDs) of the core@shell type InP@ZnS stabilized by oleylamine have been studied, with the nanoclusters consisting of CQDs of two average sizes: with core diameters of 2.1 and 3.0 nm. For the nanoclusters consisting of the particles of any of these kinds, the experimental data indicate the occurrence of Forster resonance energy transfer with an efficiency of about 50%. For the mixed nanoclusters, energy transfer has not been observed within the experimental error.

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.

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.

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.

The Forster 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.

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.

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 A 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.

Spontaneous and photoinduced protonation of 4-(2-naphthyl)pyridine (1) in solutions and in complexes with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was studied using the absorption and fluorescence spectroscopies. The structures and stabilities of complexes of compound 1 and its quaternized derivative, 1-methyl-4-(2-naphthyl)pyridinium perchlorate (3), with β-CD and HP-β-CD were examined by 1H NMR titration (logK = 1.5–2.3). The molecule of naphthylpyridine 1 is always in the cyclodextrin cavity, regardless of the pH value of the solution. 2-Hydroxypropyl-β-cyclodextrin binds better the neutral form of compound 1 than does β-CD, while naphthylpyridinium salts exhibit nearly equal affinities to both cavitands. According to spectroscopic data, pKa (1) is 5.12 in water, which favors protonation of the N atom both in the ground and excited states; as a result, the fluorescence spectrum exhibits only the band of the protonated form with a lifetime of 15 ns. The addition of HP-β-CD to a solution of naphthylpyridine 1 results in the formation of inclusion complex 1@HP-β-CD, lowers pKa to 4.62, and gives rise to a fluorescence band of the nonprotonated form of compound 1 with a lifetime of 1.25 ns. Therefore, the presence of compound 1 in the HP-β-CD cavity precludes its protonation in the excited state. The initial portions of the fluorescence curves for compound 1 in solution and in its complex with HP-β-CD obtained upon pulsed excitation were compared to propose the initiation mechanism of short-lived fluorescence of the nonprotonated form of naphthylpyridine 1. Quantum chemical modeling of the protonation and complexation of compound 1 in the presence of water was performed. Based on the results obtained, a reversible photoinduced mechanical motion of naphthylpyridine 1 in the HP-β-CD cavity was suggested.

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.

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.

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.

The quenching of the triplet-excited dyes eosine and methylene blue (MB) by H2O2 has been studied by laser and steady-state photolysis. The quenching rate constant of the eosine triplet is kq = 2.4 ± 0.3 × 105 (M s)−1 and rate constant of MB quenching with H2O2 was found to be kq = 6.5 ± 0.5 × 105 (M s)−1. The decolorization of both dyes is accelerated upon H2O2 addition under steady-state photolysis and the redox reaction mechanism is suggested. The quantum yield for ion-radicals formation obtained were: for eosine 0.01 ± 0.005 and 0.03 ± 0.01 for MB. This latter observation provides the evidence for stability of these dyes under light irradiation in the presence of H2O2.