Ashot Gevorgyan

Bio: Ashot Gevorgyan is an academic researcher from University of Rostock. The author has contributed to research in topics: Cholesteric liquid crystal & Photonic crystal. The author has an hindex of 13, co-authored 72 publications receiving 472 citations. Previous affiliations of Ashot Gevorgyan include University of Tromsø & Yerevan State University.

Regioselective and guided C-H activation of 4-nitropyrazoles.

Abstract: A divergent and regioselective approach to 5-aryl-4-nitro-1H-pyrazoles was developed by guided transition-metal-catalyzed arylation of 4-nitro-1H-pyrazoles. This method provides a convenient tool for the functionalization of the pharmacologically relevant pyrazole scaffold. The scope and limitations of the methodology were studied.

3-Methoxalylchromone—a novel versatile reagent for the regioselective purine isostere synthesis

Abstract: The first synthesis of 3-methoxalylchromone was described. The reaction of the latter with electron-rich aminoheterocycles afforded a set of heteroannelated pyridines bearing a CO2Me substituent located at the α-position of the pyridine core.

2,3-Unsubstituted chromones and their enaminone precursors as versatile reagents for the synthesis of fused pyridines

Abstract: A divergent and regioselective approach to fused pyridines was developed through formal [3 + 3] cyclocondensations from simple 2,3-unsubstituted chromones or their enaminone precursors.

Transition-metal-catalyzed arylation of nitroimidazoles and further transformations of manipulable nitro group.

Abstract: Pd- or Ni-catalyzed C–H arylation of 4-nitroimidazole derivatives directed by a manipulable nitro group was developed. The reaction tolerates a wide range of substituted aryl halides and 4-nitroimidazoles. The experiments indicated that the nitro group has influence on regioselectivity of the reaction. In addition, we have shown that the efficiency of the Suzuki–Miyaura cross-coupling reaction of nitroimidazoles is slightly lower in comparison to the direct C–H arylation. The exploration of the chemical potential of the nitro group and a putative reaction mechanism are discussed.

Magneto-Optics of a Thin Film Layer With Helical Structure And Enormous Anisotropy

Abstract: The influence of an external magnetic field onto the magneto-optical properties of media with a helical periodical structure is discussed. The case of light normal incidence is considered, and it is assumed that the external magnetic field is directed along medium axis. The transmission and reflection of the light incident normal onto a thin film having a helical structure and being in external magnetic field is discussed. The Jones matrices for this system have been constructed. It is shown that at certain values of magneto-optical activity and local anisotropy a new diffraction reflection region rises. This system can be used as a narrow-band filter with controlled bandwidth. It is shown that at certain conditions this system can work also as an ideal optical diode or one-sided reflector. The specific features of eigenpolarizations are also discussed, and it is shown that the very dependences of eigenpolarizations onto external magnetic field direction conditions great values of nonreciprocal transmission.

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

Abstract: Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control of optical quantum systems.

Dialkylbiaryl phosphines in Pd-catalyzed amination: a user's guide

Abstract: Dialkylbiaryl phosphines are a valuable class of ligand for Pd-catalyzed amination reactions and have been applied in a range of contexts. This perspective attempts to aid the reader in the selection of the best choice of reaction conditions and ligand of this class for the most commonly encountered and practically important substrate combinations.

Principles of lasers

Abstract: Manuscript received April 14, 1983; revised June 24, 1983. N. B. Abraham is with the Department of Physics, BrynMawr College, Bryn Mawr, PA 19010. P. Mandel is with the Service de Chimie Physique 11, Universite Libre de Bruselles, Brussels, Belgium. L. W. Casperson is with the Department of Electrical Engineering and Applied Science: University of California, Los Angeles, CA 90024. Editor’s Note: A similar correction by Dr. F. Holigner and Prof. Dr. H. Weber of the Universitat Kaiserslautern was received on May 4, 1983. tions can be expressed as BR = y + p P (3a j