Sergei A. Tikhomirov

Bio: Sergei A. Tikhomirov is an academic researcher from National Academy of Sciences of Belarus. The author has contributed to research in topics: Excited state & Luminescence. The author has an hindex of 9, co-authored 81 publications receiving 380 citations. Previous affiliations of Sergei A. Tikhomirov include Semenov Institute of Chemical Physics.

S2 → S0 fluorescence and transient Sn ← S1 absorption of all-rans-β-carotene in solid and liquid solutions

Abstract: The spectral and luminescence characteristics of all-rans-β-carotene* were studied at 77 and 4.2 K in isopentane. The fluorescence spectra exhibit a vibronic structure; their 00 band halfwidths are 770 cm−1 at 77 K and 380 cm−1 at 4.2 K. Fluorescence quantum yields ϱ at 4.2 and 77 K are (8 ± 3) × 10−5 and (4 ± 2) × 10−5 respectively. The lifetimes of the observed fluorescence, estimated from the fluoroescence quantum yields ϱ and the natural fluorescence lifetimes, appear to be (8 ± 3) × 10−14 s at 4.2 K and (4 ± 2) × 10−14 s at 77 K. The fluorescence observed originates from the S2(1 1B+u state; the extremely short lifetime of the latter is due to its electronic relaxation to the lowest S1(2 1A−g) state. The S1 state of β-carotene was studied at 293 K using picosecond laser spectroscopy (λexc = 528 and 352 nm). The Sn ← S1 absorption spectrum in n-hexane has a maximum at 555 nm (18 000 cm−1). In toluene and chinoline, bathochromic shifts of 400 ± 100 and 800 ± 100 cm−1 are observed relative to the maximum in n-hexane. The Sn ← S1 transition to the higher excited state Sn can take place; the spectrum of the Sn ← S0 absorption to this state has a maximum at 275 nm (36 500 cm−1 in n-hexane. The lifetime of the S1 state of β-carotene in solvents with different viscosities and polarities (n-hexane, toluene, chinoline and vaseline oil) is 10 ± 2 ps.

Picosecond dynamics of singlet excited states of oxotetrahydrobenzo[c]phenanthridine in protic and aprotic solvents

Abstract: The spectral and kinetic properties of singlet excited states of two tetrahydrobenzo[c]phenanthridines—3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-one (DTP) and 3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-ol (DTP1)—are studied by picosecond absorption and luminescence spectroscopy in protic and aprotic solvents at 293 and 77 K. Based on the differences in the spectral and luminescent properties of DTP and DTP1, it was shown that the oxygen atom involved in the conjugation system of DTP is responsible for the formation of hydrogen-bonded complexes with alcohols. In the picosecond spectra of the induced absorption of DTP in n-hexane and acetonitrile, two bands peaked at 480 and 600 nm are observed, which are caused by the Tk ← T1-and Sn ← S1 absorption of DTP molecules solvated by the solvent by means of universal intermolecular interactions. In alcohols (methanol, ethanol, and n-propanol), an additional band is observed at 850 nm, which is caused by the Sm ← S1 absorption of hydrogen-bonded complexes. From analysis of the kinetics of the rise and decay of the induced absorption of DTP in n-hexane, acetonitrile, and alcohols, it is suggested that the main nonradiative channel in DTP is intersystem crossing.

Decay of electronic excitations in CdS and CdS/ZnS colloidal quantum dots: spectral and kinetic investigations

Abstract: Using the spectral methods of induced absorption, luminescence, and photostimulated luminescence flash, we have experimentally investigated processes of decay of electronic excitations in CdS colloidal quantum dots and in CdS/ZnS “core-shell” systems synthesized in gelatin by the sol-gel method. It has been shown that the decay of electronic excitations in colloidal quantum dots of this type is predominantly related to a fast localization of nonequilibrium charge carriers on surface defects and their subsequent recombination during times on the order of units and tens of picoseconds. The passage to core-shell systems eliminates, to a large extent, surface defects of the core, some of which are luminescence centers. However, upon using the sol-gel synthesis, a noticeable fraction of luminescence centers are formed in the interior of the CdS quantum dot, which, as well as in the case of CdS/ZnS systems, ensures localization of exciton, blocks its direct annihilation, and maintains recombination radiation.

Femtosecond Dynamics of Optically Induced Anisotropy of Complex Molecules in the Gas Phase

Abstract: The evolution of optically induced anisotropy in an equilibrium ensemble of free asymmetric tops under collisionless conditions has been investigated theoretically and experimentally. The dynamics of the orientation correlation functions has been studied, the results of femtosecond experiments on measurement of relaxation of the optically induced anisotropy for perylene in the gas phase are presented, and their interpretation within the framework of the theory developed is given. It is shown that in contrast to stationary anisotropy, its time kinetics has more complete characteristic information about the dynamics of vector correlations in a molecular ensemble.

Principles Of Fluorescence Spectroscopy

Abstract: Thank you very much for downloading principles of fluorescence spectroscopy. As you may know, people have look hundreds times for their favorite novels like this principles of fluorescence spectroscopy, but end up in malicious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they cope with some harmful bugs inside their desktop computer. principles of fluorescence spectroscopy is available in our digital library an online access to it is set as public so you can download it instantly. Our digital library spans in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the principles of fluorescence spectroscopy is universally compatible with any devices to read.

Theory of the linear and nonlinear optical properties of semiconductor microcrystallites

Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.

Xanthones from fungi, lichens, and bacteria : the natural products and their synthesis

Abstract: Many fungi, lichens, and bacteria produce xanthones (derivatives of 9H-xanthen-9-one, “xanthone” from the Greek “xanthos”, for “yellow”) as secondary metabolites. Xanthones are typically polysubstituted and occur as either fully aromatized, dihydro-, tetrahydro-, or, more rarely, hexahydro-derivatives. This family of compounds appeals to medicinal chemists because of their pronounced biological activity within a notably broad spectrum of disease states, a result of their interaction with a correspondingly diverse range of target biomolecules. This has led to the description of xanthones as “privileged structures”.(1) Historically, the total synthesis of the natural products has mostly been limited to fully aromatized targets. Syntheses of the more challenging partially saturated xanthones have less frequently been reported, although the development in recent times of novel and reliable methods for the construction of the (polysubstituted) unsaturated xanthone core holds promise for future endeavors. In particular, the fascinating structural and biological properties of xanthone dimers and heterodimers may excite the synthetic or natural product chemist.

The photochemistry and function of carotenoids in photosynthesis

Abstract: In photosynthetic systems, carotenoids act as light-harvesting molecules and provide photoprotection of the plant and bacterial species (Cogdell and Frank 1987; Siefermann-Harms 1985). In many cases, themanner in which aparticular carotenoid functions depends on its photochemical properties. Carotenoids participate in an abundance of photochemical reactions including singlet-singlet energy transfer, triplet-triplet energy transfer, oxidation, reduction and isomerisation. Carotenoid molecules are capable of reporting information about the course of these reactions from readily observable changes in many of their molecular spectroscopic properties.