N. N. Denisov

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.

OCT‐guided laser hyperthermia with passively tumor‐targeted gold nanoparticles

The goal of this study is the development of a method of local laser hyperthermia with gold nanoparticles under noninvasive optical monitoring of nanoparticle accumulation in tumor tissue in vivo. Bifunctional plasmon resonant nanoparticles that are optimal for OCT diagnostics and laser heating at the wavelength of 810 nm were used in the study. The OCT examination showed that the accumulation of gold nanoparticles in the tumor invading into skin was maximal 4-5 h after intravenous injection. It was demonstrated that nanoparticle accumulation in tumor allowed more local heating and enhanced thermal sensitivity of tumor tissue. Laser hyperthermia that heated tumor up to 44-45 °C at maximum nanoparticle accumulation induced apoptotic death of tumor cells and inhibited tumor growth by 104% on the 5th day after treatment.

Photoreduction of graphite oxide at different temperatures

The photoreduction of graphite oxide in a film exposed to UV light is investigated at 77 K and at room temperature. At a temperature of 77 K, the photodissociation of oxygen-containing groups and graphite oxide (GO) reduction occurs that is observed in the UV-vis and Raman absorption spectra. The mechanism of photoreduction is proposed, and a comparison of the photoreduction and the thermal process is carried out.

Inactivation of Pathogenic Microorganisms in the Photocatalytic Process on Nanosized TiO2 Crystals

The kinetics of the photocatalytic oxidation of E. coli gram-negative bacteria and the basic components of the cell wall membrane (LPS, PE, and PGN) on a porous film composed of TiO2 nanoparticles was studied using frustrated total internal reflection FTIR spectroscopy. Structural changes in the cell wall membrane at the initial stage of cell oxidation were revealed. It was demonstrated that the cell’s organic material is photocatalytically oxidized in such a manner that the TiO2 surface is cleaned. Laser photolysis experiments demonstrated that the organic material of the cell wall membrane reduces holes in the valence band of TiO2.

Photochemical Reduction of Graphite Oxide

The spectral and photochemical properties of graphite oxide (GO) in films have been examined. The photochemical reduction of GO has been studied using optical absorption, IR and Raman spectroscopy, and mass spectroscopy. The molecular model of photoprocesses has been considered, and a domain model of photoreduction has been suggested.

Effect of humidity on the conductivity of graphite oxide during its photoreduction

The influence of humidity on the conductivity of graphite oxide (GO) films has been considered. Graphite oxide films of a 200–500 nm thickness become conductors to have a conductivity of 10−6 to 10−2 S/cm when humidity increases from 30 to 100%. Film morphology varies during the course of water diffusion. Ultraviolet light-mediated reduction of GO decreases the sensitivity to humidity until its complete disappearance.

DYNAMICS OF CONTACT RADICAL ION PAIRS C60-AROMATIC AMINES : A STUDY BY PICOSECOND LASER PHOTOLYSIS

Charge transfer complexes between C60 and ternary aromatic amines (N,N,N,N′-tetramethyl-p-phenylenediamine,p-methoxy-N,N-dimethylaniline,p-methyl-N,N-dimethylaniline,N,N-diethylaniline,N,N-dimethylaniline, and triphenylamine) were studied in chlorobenzene solutions. The lifetimes of the excited state with charge transfer in these complexes were measured by the method of picosecond laser photolysis. The dependence of the rate constant of the back electron transfer on ΔG in the back electron transfer reaction with relaxation of the charge-transfer state exhibits the “Marcus-inverted” region.

Interaction of the iridium(III) trihydridophosphine complex with fullerene C60 under thermal and photochemical excitation

The interaction of the PPh3-stabilized iridium trihydrido complex H3Ir(PPh3)3 with fullerene C60 under thermal and photochemical excitation was studied under anaerobic conditions. Heating (100 °C) or photolysis by the visible light of the H3Ir(PPh3)3-C60 650 nm, which are characteristic of the ·2-coordinated C60 in several fullerene-containing metal complexes. The kinetic behavior of the H3Ir(PPh3)3)-C60 system in benzonitrile was investigated using a Nd3+-YAG laser (λ=532 nm). The quenching rate constant determined from the dependence of the effective first-order quenching constant of C60(T) on the concentration of H3Ir(PPh3)3 is equal to 1.1·109 L mol−1 s−1. The quenching of C60(T) by the iridium hydridophosphine complex follows the reductive mechanism to form a C60 monoanion. The ESR signal with g=2.000 and ΔH=0.17 mT (at room temperature) and characteristic absorption bands in the near-IR region at 940, 1004, and 1076 nm support the formation of the C60 monoanion during the interaction of the triplet-excited C60 with H3Ir(PPh3)3.

Photophysical properties of (η2-C60)Pd(PPh3)2 complex in benzene. Picosecond and nanosecond laser photolysis

Absorption spectra of the photoexcited (η2-C60)Pd(PPh3)2 complex in benzene were obtained by picosecond and nanosecond laser photolysis. The spectra are compared with those observed for photoexcited states of fullerene C60 and charge-transfer states of C60 complexes with ternary amines. The relaxation kinetics of excited (η2-C60)Pd(PPh3)2 complex has three components with characteristic lifetimes τ1 = 43 ps, τ2 = 1500 ps, and τ3 = 1.17 μs. The results are discussed in terms of the four-level scheme of the excited complex.