V. A. Orlovich

Intermolecular interaction of photoexcited Cu(TMpy-P4) with water studied by transient resonance Raman and picosecond absorption spectroscopies

photoinduced complex between Cu(TMpy-P4) and water molecules, reversibly axially coordinated to the central metal, was observed in picosecond transient absorption and nanosecond resonance Raman experiments. This complex is rapidly created (τ1 = 15 ± 5 ps) in the excited triplet (π, π*) state of Cu-porphyrin, and the subsequent relaxation is proposed to proceed via two parallel pathways. One is fast and efficient (≥90% of molecules), and presumably involves a (π, d) charge-transfer state. The second pathway is slow (τ2 >> 1 ns), has a low quantum yield (≤10%) and involves the excited (d, d) state which is responsible for transient Raman features at ≈ 1553 cm−1 (ν2*) and ≈ 1347 cm−1 (ν4*), and for low-intensity long-lived transient absorption features.

Resonance Raman Study on Photoinduced Interaction of Water-Soluble Cu-Porphyrin with Short Oligothymidylates

It is known that water-soluble copper(II) porphyrin Cu(TMpy-P4) interacts in a specific manner with DNA and some DNA-model poly- and oligonucleotides creating a photoinduced exciplex in the excited state with CO group of thymine [1]. However, the questions remained to be solved about the minimal length of nucleotide and possible role of a secondary structure of polymer required for the exciplex formation. To bring more light into the problem, spectroscopic studies on CuP in interaction with a series of short oligothymidylates d(pT)n, n=1.¨4, has been performed. Picosecond transient absorption (TA) study of these complexes has been reported previously [2, 3]. In this work, we present results of Raman characterization of photoinduced intermolecular interactions between CuP and short oligothymidylates, as well as comparative study of CuP in water and in interaction with poly(dA-dT)2. Analysis of transient Raman spectra (Figure 1), together with TA data obtained previously, revealed the existence of several different types of exciplex formed after photoexcitation. We can distinguish excited CuP complexes with water and CO group of thymine which, in general, can coexist in a solution. Exciplex species were detected in transient RR spectra as new bands shifted in the low-frequency region relatively to their ground state counterparts. In the case of CuP-water interaction (Figure 1, curve A) intensity of v2 * and v4* exciplex bands at 1552 and 1348 cm−1, respectively, is not more than 10% of v2 and v4 ground state ones. For CuP-d(pT)n complex substantial increase of the intensity of transient bands is observed in comparison with CuP-water exciplex (Figure 1, curves B-E). Exciplex bands grows continuously with increasing of the number of thymine residues in oligonucleotides. As for CuP in poly(dA-dT), excited complex bands dramatically increase in intensity and become dominate in transient RR spectra (Figure 1, curve F).

Resonance Raman and Transient Absorption Studies on Ni(TMpy-P4) in a Water Buffer and Bound to DNA Model Compounds: Excited-States Dynamics and State of Coordination

Nanosecond resonance Raman (RR) spectra of water-soluble Ni(TMpy-P4) bound to DNA model compounds, poly(dA-dT) and poly(dG-dC), show prominent transient features under increasing power density of the excitation pulses. Careful comparison with RR spectra of four- and six-coordinate Ni(TMpy-P4) in water buffer, as well as of the related Ni(II)-porphyrin, Ni-TPP, in both non-coordinating (like benzene) and coordinating nitrogen-containing solvents, revealed that it is the low-lying excited (d,d) state of Ni(TMpy-P4) that manifests itself in RR spectra under increasing excitation power density (Figure 1). The results of picosecond transient absorption studies on the kinetics and relaxation pathways for Ni(TMpy-P4) in different molecular environment are also presented. Although transient RR spectra of Ni(TMpy-P4) in both poly(dA-dT) and poly(dG-dC) reveal similar peculiarities, application of picosecond absorption technique permits to find distinct difference in photophysics of above mentioned objects, depending on the type of Ni-porphyrin complexation with the polynucleotides, with more complex behaviour for Ni(TMpy-P4) in poly(dA-dT).

Direct observation of laser phase changes during solition generation in stimulated raman scattering

carrying out a quantum non-demolition measurement for such a pulse system with coupled modes. For our approach, the non-demolition measurements in both quadratures and in photon number have been analyzed and a suggestion for a multichannel scheme is given as well. In the present paper, the detection of nonclassical light in the real experiment is considered for two types of optical fibers with a spatial beating of the energy between interacting modes: for a periodically inhomogeneous-in-space fiber and for a dual-core tunnelly coupled one. The analysis shows that a good quantum non-demolition measurement is only possible for a strongly squeezed light, and a practically ideal quantum nondemolition measurement could be obtained for such types of optical fibers at relatively low power requirements. The developed approach is also very successful for a study of the problem of generation of quantum states for two coupled solitons. A clear description of the stability domains enlights the existence of instability phenomena, and bifurcations have been obtained in the frames of well-known physical models (e.g., described by the Duffing and/or Mathier equations). We ascertained that a controllable quantum chaos can be identified for a squeezed light in such a system under conditions when the non-demolition measurements take place. The polarized squeezed light has been obtained as well for discussed nonlinear coherent coupling. The Stokes parameters formalism is used for an analysis of polarized chaos in a dual-core optical fiber, and the solution has been written in an exact analytical form. The experimental setup, using the correlation technique, for a verification of such quantum states of light is proposed and the numerical estimations show that the effect can be observed for real conditions.