Solvatochromic effect on photophysical properties of Quinoxalin-2(1H)-one and 3-Benzylquinoxalin-2(1H)-one

Quinoxalin-2(1H)-one and its derived 3-Benzylquinoxalin-2(1H)-one were synthesized and characterized by UV–visible spectroscopy. The changes displayed by the photophysical properties of these molecules in different solvents can be explained in terms of a sum of dielectric polarity and hydrogen bonding effects taking part in the stabilisation of the structure. 3-Benzylquinoxalin-2(1H)-one exhibits two fluorescence emission bands (F _a and F _n) in very polar solvents and one band (F _n) in low polar solvents. These bands are assigned on the basis of the absorption and emission solvent effect. The abnormal fluorescence (F _a) observed in very polar solvents is attributed to an intermolecular interaction between solute and solvent molecules in the excited state (exciplex formation).     

Magnetoresistance of a highly correlated electron liquid

The behavior in a magnetic field of a highly correlated electron liquid approaching the fermion condensation quantum phase transition from the disordered phase is considered. We show that, at sufficiently high temperatures T≥T*(x), the effective mass starts to depend on T, M* ∝T^?1/2. This T^?1/2 dependence of the effective mass at elevated temperatures leads to the non-Fermi liquid behavior of the resistivity, σ(T) ∝ T and at higher temperatures σ(T) ∝ T^3/2. The application of a magnetic field B restores the common T² behavior of the resistivity. The effective mass depends on the magnetic field, M*(B) ∝ B^?2/3, being approximately independent of the temperature at T≤T*(B) ∝ B^4/3. At T≥T*(B), the T^?1/2 dependence of the effective mass is reestablished. We demonstrate that this B-T phase diagram has a strong impact on the magnetoresistance (MR) of the highly correlated electron liquid. The MR as a function of the temperature exhibits a transition from negative values of MR at T→0 to positive values at T ∝ B^4/3. Thus, at T≥T*(B), MR as a function of the temperature possesses a node at T ∝ B^4/3.     

Synthesis,Spectroscopic Characterization and DFT/TD-DFT Calculations of new Fluorescent Derivatives of Imidazo[4′,5′:3,4]Benzo[<Emphasis Type="Italic">c</Emphasis>]Isoxazole

An increasingly wide variety of fluorescent compounds is used in biotechnology, genomics, immunoassays, array technologies, imaging, and drug discovery. Therefore, synthesis of fluorophores with novel structural features can be interesting and useful in various fields. In this paper, four new fluorescent heterocyclic compounds with high quantum yields are introduced. These new fluorophores are synthesized in moderate to high yields via regioselective nitration of 3-alkyl-8-(4-chlorophenyl)-3 H-imidazo[4′,5′:3,4]benzo[c]isoxazoles. The latter compounds are obtained from the reaction of 1-alkyl-5-nitro-1 H-benzoimidazoles with (4-chlorophenyl)acetonitrile in basic MeOH solution. Physical spectral (UV-vis, IR, ¹HNMR, ¹³C NMR, NOESY and fluorescence) and analytical data have established the structures of synthesized compounds. The fluorescence properties of new fluorescent heterocyclic compounds are studied. The fluorescence of all compounds is very intense and fluorescence quantum yields are high (> 0.52). Density functional theory (DFT) calculations are performed to provide the optimized geometries, relevant frontier orbitals and the prediction of ¹H NMR chemical shifts for confirming the exact structure of fluorescent compounds. Calculated electronic absorption spectra were also obtained by time-dependent density functional theory (TD-DFT) method.

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Control of Quantum Echo and Bell State Swapping of Two Atomic Qubits in the Two-Mode Vacuum Field Environment

We investigate quantum echo control and Bell state swapping for two atomic qubits (TAQs) coupling to two-mode vacuum cavity field (TMVCF) environment via two-photon resonance. We discuss the effect of initial entanglement factor ?? and relative coupling strength R=g₁/g₂ on quantum state fidelity of TAQs, and analyze the relation between three kinds of quantum entanglement(C(ρ_a),C(ρ_f),S(ρ_a)) and quantum state fidelity, then reveal physical essence of quantum echo of TAQs. It is shown that in the identical coupling case R=1, periodic quantum echo of TAQs with π cycle is always produced, and the value of fidelity can be controlled by choosing appropriate ?? and atom-filed interaction time. In the non-identical coupling case R≠1, quantum echoes with periods of π, 2π and 4π can be formed respectively by adjusting R. The characteristics of quantum echo results from the non-Markovianity of TMVCF environment, and then we propose Bell state swapping scheme between TAQs and two-mode cavity field.     

Measurement of isotope shifts of gadolinium levels by laser-induced fluorescence spectroscopy

The results of isotope shift measurements for the gadolinium atom both in a hollow cathode lamp and in an atomic beam are described. Using laser-induced fluorescence spectroscopy, the measurements were performed for four transitions, which are related to the configurations 4f⁷5d6s²⁹D to 4f⁷5d6s6p⁹D and 4f⁷5d6ss6p⁹FD.     

A highly Selective Fluorescent Sensor for Monitoring Cu<Superscript>2+</Superscript> Ion: Synthesis,Characterization and Photophysical Properties

A new fluorescent sensor, 4-allylamine-N-(N-salicylidene)-1,8-naphthalimide (1), anchoring a naphthalimide moiety as fluorophore and a Schiff base group as receptor, was synthesized and characterized. The photophysical properties of sensor 1 were conducted in organic solvents of different polarities. Our study revealed that, depending on the solvent polarity, the fluorescence quantum yields varied from 0.59 to 0.89. The fluorescent activity of the sensor was monitored and the sensor was consequently applied for the detection of Cu²⁺ with high selectivity over various metal ions by fluorescence quenching in Tris-HCl (pH = 7.2) buffer/DMF (1:1, v/v) solution. From the binding stoichiometry, it was indicated that a 1:1 complex was formed between Cu²⁺ and the sensor 1. The fluorescence intensity was linear with Cu²⁺ in the concentration range 0.5–5 μM. Moreso, the detection limit was calculated to be 0.32 μM, which is sufficiently low for good sensitivity of Cu²⁺ ion. The binding mode was due to the intramolecular charge transfer (ICT) and the coordination of Cu²⁺ with C = N and hydroxyl oxygen groups of the sensor 1. The sensor proved effective for Cu²⁺ monitoring in real water samples with recovery rates of 95–112.6 % obtained.     

Spectroscopy and photophysics of chloro-bis-bipyridyl complexes of ruthenium(II) with pyridine ligands

The absorption, luminescence, and luminescence excitation spectra of ruthenium(II) complexes cis-[Ru(bpy)₂(L)Cl]⁺[bpy=2,2′-bipyridyl; L=NH₃, pyrazine, pyridine, 4-aminopyridine, 4-picoline, isonicotinamide, 4-cyanopyridine, 4,4′-bipyridyl, or trans-1,2-bis(4-pyridyl)ethylene] in alcoholic (4: 1 EtOH-MeOH) solutions are studied. At 77 K, the quantum yields and decay times of the luminescence of the complexes are measured and the deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer state (³MLCT) are determined. The linear correlation between the energy of the lowest state ³MLCT d _π(Ru)>π*(bpy) of the cis-[Ru(bpy)₂(L)Cl]⁺ complexes and the parameter pK_a of the free 4-substituted pyridines and pyrazine used as ligands is established.     

A theoretical investigation of the effect of water on the structure and fluorescence spectra of L-tryptophan

Fluorescence spectra of two long-wavelength electron transitions S₀ ← ¹L_b and S₀ ← ¹L_a in uncharged and zwitterionic forms of L-tryptophan (Trp) in aqueous solution and in the complex of Trp with water molecule were calculated using the Frank–Condon approximation. Geometric parameters of Trp in electronically excited states were determined, and the vibrational structure of vibronic spectra was analyzed. It was shown that the relative position of structural fragments of alanine (R-Ala) and indole (R-In) could have a determining effect on the fluorescence and formation of the vibrational structure of electronic spectra. The increase of the rotation angle between the R-Ala and R-In, which depends on the Trp environment, results in the Trp fluorescence originating only from the singlet excited state ¹L_a.     

Spin-selective low temperature spectroscopy on single molecules with a triplet-triplet optical transition: Application to the NV defect center in diamond

The spin-selective photokinetics of a single matrix-isolated impurity molecule with a triplet-triplet optical transition, T ₀–T ₁, is considered and the manifestations of the photokinetics in the fluorescence excitation spectra and intensity autocorrelation functions g ⁽²⁾(τ) of the molecule undergoing narrow-band optical excitation is studied to resolve the fine structure of the transition. The rates of intersystem crossings (ISCs) T ₁→S→T ₀ to and from a nonradiating singlet state S of the molecule and the rate of population relaxation among the ground (T ₀) state sublevels can be obtained from the spectra and g ⁽²⁾(τ) using the analytical expressions obtained. New experiments on an individual NV defect center in nanocrystals of diamond, where, for the first time, the fine structure of its triplet-triplet ³ A-³ E zero-phonon optical transition (~637 nm) at 1.4 K was resolved, are interpreted. It is concluded that the rate of the ISC transition from the m _S =0 sublevel of the excited ³ E state to the singlet ¹ A state (~1 kHz) is much slower than the rates from the m _S =±1 substates, while the rates of ISC transitions to different m _S substates of the ground ³ A state are close to each other (~1 Hz). As a result, only the optical transition between m _S =0 sublevels in the ³ A-³ E manifold contributes strongly to the fluorescence. The experimentally observed double-exponential decay of the g ⁽²⁾(τ) function is explained by the two pathways available to the center for it to leave the S state: (i) the S→ T ₀(m _S )=0) transition and (ii) the S→T ⁰(m _S =±1) transitions followed by the slow spin-lattice relaxation T ₀(m _S =±1)→T ₀(m _S =0) (rate ~0.1 Hz). The work is important for studies where the NV center is used as a single photon source or for quantum information processing.     

Collisional depolarization of fluorescence of polyatomic molecules in the gas phase by excited state quenchers

A new method of extracting information on the efficiencies of quenching of an excited state and collisional reorientation from the data on the fluorescence depolarization of molecular vapors by quenchers of the excited state is proposed. The method does not involve collisional cross sections and fluorescence lifetimes. From the experimental data on the depolarization of polarized luminescence of para-quaterphenyl and 2-(4′-dimethylamine) phenyl-5-phenyloxydiazole by oxygen and nitrogen, the ratios of the constants of the excitedstate quenching and orientation randomization (fluorescence depolarization) by oxygen are obtained. For these molecules, the probabilities of the excited-state quenching q and orientation randomization s per collision with oxygen molecules are determined (q=0.25±0.04 and s=0.13±0.04 for para-quaterphenyl and q=0.2±0.04 and s=0.21±0.04 for 2-(4′-dimethylamine)phenyl-5-phenyloxydiazole). The self-quenching of fluorescence of perylene vapors, with the probability 0.28 per collision, is found.     

Synthesis,DNA/HSA Interaction Spectroscopic Studies and In Vitro Cytotoxicity of a New Mixed Ligand Cu(II) Complex

A new mixed ligand copper(II)-dipeptide complex with 2-(2′-pyridyl)benzothiazole (pbt), [Cu(Gly-L-leu)(pbt)(H₂O)]·ClO₄ (Gly-L-leu = Glycyl-L-leucine anion) was synthesized and characterized by various physico-chemical means. The DNA binding and cleavage properties of the complex investigated by viscosity, agarose gel electrophoresis and multi-spectroscopic techniques (UV, circular dichroism (CD) and fluorescence) showed that the complex was bound to CT-DNA through intercalation mode with moderate binding constant (K _b = 3.132 × 10⁴ M^?1), and cleaved pBR322 DNA efficiently (~ 5 μM) in the presence of Vc, probably via an oxidative mechanism induced by ?OH. Additionally, the interaction of the complex with human serum albumin (HSA) was explored by UV-visible, CD, fluorescence, synchronous fluorescence and 3D fluorescence spectroscopy. The complex exhibits desired affinity to HSA through hydrophobic interaction. Moreover, the cytotoxicity of the complex against three human carcinoma cell lines (HeLa, HepG2 and A549) was evaluated by MTT assay, which showed that the complex had effective cytotoxicity and higher inhibition toward A549 cell lines with IC₅₀ of 38.0 ± 3.2 μM.     

Exact asymptotic form for the β function in quantum electrodynamics

It is shown that the asymptotic form of the Gell-Mann-Low function in quantum electrodynamics can be determined exactly: β(g) = g for g → ∞, where g = e ² is the running fine-structure constant. This solves the problem of electrodynamics at small distances L (for which dependence g ∞ L ^?2 holds) and completely eliminates the problem of “zero charge.”     

A Bohmian approach to the perturbations of non-linear Klein–Gordon equation

In the framework of Bohmian quantum mechanics, the Klein–Gordon equation can be seen as representing a particle with mass m which is guided by a guiding wave ?(x) in a causal manner. Here a relevant question is whether Bohmian quantum mechanics is applicable to a non-linear Klein–Gordon equation? We examine this approach for ?⁴(x) and sine-Gordon potentials. It turns out that this method leads to equations for quantum states which are identical to those derived by field theoretical methods used for quantum solitons. Moreover, the quantum force exerted on the particle can be determined. This method can be used for other non-linear potentials as well.     

Supramolecular Interaction of Two Tryptophans with <Emphasis Type="Italic">p</Emphasis>-sulfonated calix[<Emphasis Type="Italic">4,6,8</Emphasis>]arene

The complex characteristics of p-sulfonated calix[n]arene (SCnA) and two tryptophans N-[(tert-butoxy) carbonyl]-tryptophan (trp-A) and N-carbobenzoxy-tryptophane (trp-B) were examined through various techniques. Spectrofluorimetry was performed at different temperatures to determine the stability constants and evaluate the thermodynamic parameters of the two complexes. The effect of pH on complex formation was estimated. According to the fluorescence data, the assumption about the steric hindrance of the tert-butyl group of trp-A and the phenyl group of trp-B was put forward. ¹H NMR was also performed to determine the binding interaction mechanism. Results showed that the indole benzene rings of the two tryptophans partly penetrated into the cavity of p-sulfonated calix[n]arene. The shift in Ha, Hb and Hc, Hd positions became more significant as the number of phenolic units of the calixarene ring increased. Molecular modeling of the complexes elucidated the assumption about the steric hindrance of the tert-butyl group of trp-A and the phenyl group of trp-B. These observations of molecular modeling computation are consistent with previous fluorescence data and ¹H NMR results.     

Experimental Research to Confirm the Excitation of Gamov–Teller Resonance in Compound Nucleus <Superscript>118</Superscript>Sb

At proton energies of 4–9 MeV, trial experimental investigations were performed to confirm the excitation of Gamov–Teller resonance (GTR) 1⁺ in the compound nucleus ¹¹⁸Sb discovered by B.Ya. Guzhovskiy’s research group in the ¹¹⁷Sn(p,xn) reaction at proton energies of 7.2 MeV (the first component is GTR1) and 9.9MeV (the second component is GTR2). The ¹¹⁷Sn(p,xn) reaction was used, whose neutrons and background neutrons were registered by an all-wave long counter arranged at an angle of 140° to the direction of the proton beam propagation. Simultaneously, along with the registration of neutrons, elastically and inelastically scattered protons at angles of 20° and 160° were registered. At the proton energy equal to ~7.2 MeV, in the excitation functions for ¹¹⁷Sn(p,xn), ¹¹⁷Sn(p,p₀), and ¹¹⁷Sn(p,p₄)¹¹⁷Sn* (1004.5 keV, 3/2⁺), a resonance with a width of ≈1.2 MeV having an energy structure was discovered. Its possible quantum numbers are 1⁺.     

Fluorescence of the <Emphasis Type="Italic">cis</Emphasis>-dimers of porphyrins containing ethylene bridges

The absorption and fluorescence spectra of solutions of the porphyrin dimers containing ethylene bridges, binding two Zn(II)octaethylporphyrin molecules or one Zn(II)octaethylporphyrin and one octaethylporphyrin molecule into cis conformation, were studied. For both studied cis-dimers, structureless absorption spectra were observed, only in general resembling the spectra of initial molecules, as well as weak fluorescence with a wide bell-shaped spectrum with a maximum at 680–700 nm and a quantum yield of about Φ_f≈3×10^?5, which is three orders of magnitude lower as compared to the fluorescence of initial monomeric porphyrins. A strong dependence of the fluorescence yield on a medium viscosity was revealed. In addition, low-yield irreversible cis-trans photoisomerization of cis-dimers was detected. A mechanism responsible for the strong intramolecular quenching of fluorescence of the porphyrin dimers containing ethylene bridges is suggested to be a conformation transformation in the region of the ethylene bridge, leading the molecular system to the region of “conic crossing” of the energy surfaces of excited and ground electron states.     

Quantum Image Encryption Based on Iterative Framework of Frequency-Spatial Domain Transforms

A novel quantum image encryption and decryption algorithm based on iteration framework of frequency-spatial domain transforms is proposed. In this paper, the images are represented in the flexible representation for quantum images (FRQI). Previous quantum image encryption algorithms are realized by spatial domain transform to scramble the position information of original images and frequency domain transform to encode the color information of images. But there are some problems such as the periodicity of spatial domain transform, which will make it easy to recover the original images. Hence, we present the iterative framework of frequency-spatial domain transforms. Based on the iterative framework, the novel encryption algorithm uses Fibonacci transform and geometric transform for many times to scramble the position information of the original images and double random-phase encoding to encode the color information of the images. The encryption keys include the iterative time t of the Fibonacci transform, the iterative time l of the geometric transform, the geometric transform matrix G i which is n × n matrix, the classical binary sequences K (\(k_{0}k_{1}{\ldots } k_{2^{2n}-1}\)) and \(D(d_{0}d_{1}{\ldots } d_{2^{2n}-1}\)). Here the key space of Fibonacci transform and geometric transform are both estimated to be 2²⁶. The key space of binary sequences is (2 ^n×n ) × (2 ^n×n ). Then the key space of the entire algorithm is about \(2^{2{n^{2}}+52}\). Since all quantum operations are invertible, the quantum image decryption algorithm is the inverse of the encryption algorithm. The results of numerical simulation and analysis indicate that the proposed algorithm has high security and high sensitivity.     

Theoretical Analysis of the Fluorescence Spectra of 7-Azaindole and Its Tautomer

The electronic—vibrational fluorescence spectra of the first, S₀ → ¹L_b, and second, S₀ → ¹L_a, electronic transitions of 7-azaindole and its tautomer for an isolated state have been calculated. Specific features of structural changes in 7-azaindole and its tautomer upon electronic excitation are determined. Vibrational spectra are assigned for the ground state, and the vibrational structure of fluorescence spectra is interpreted. It is shown that the intensity redistribution between the 6a and 6b oscillations, which is observed in the fluorescence spectrum of the S₀ → ¹L_b transition in 7-azaindole, can be explained as a result of intensity borrowing (according to the Herzberg—Teller mechanism) from the ¹L_a state.