Spectral-luminescent properties of condensation products of 8-aminoquinoline,aromatic aldehydes,and dimedone

Hydrobenzophenanthrolinone derivatives were synthesized by three-component condensation of 8-aminoquinoline, aromatic aldehydes, and dimedone. The structures of the obtained substances were confirmed by NMR and IR spectroscopy and mass spectrometry. Spectral-luminescent investigations of the synthesized compounds showed that they were characterized by high oscillator strengths for allowed electronic transitions S _n ← S ₀ (n = 1–3). Low fluorescence quantum yields in EtOH (Φ_fl ~ 10^–4–10^–3) and an increase of the Φfl values in toluene (~10^–2) at room temperature and with lowering the temperature to 77 K (Φ_fl ~ 10^–1) for a number of the compounds under study were satisfactorily explained within the framework of Marcus theory.     

Fluorescence spectroscopy of potential electroluminescent materials: Substituent effects on DSB and segmented PPV derivatives

The absorption and fluorescence of substituted distyrylbenzene (DSB) derivatives and segmented poly(phenylene vinylene) (PPV) derivatives are characterized by long-wavelength absorption maxima and absorption coefficients of λ_a = 380–450 nm, ε = 20,000–60,000 M⁻¹ cm¹ and fluorescence maxima, quantum yields, and decay times of λ_r = 440–530 nm, Φ_f = 0.2–0.9, and Τ = 0.8–2.5 ns, respectively. Alkoxy substituents at the central phenylene ring of DSB groups increase the bathochromic shift in the spectra in comparison to DSB, without a significant decrease in the high DSB fluorescence quantum yield. Both phenyl and cyano substitutions at the vinylene bridge lead to a further bathochromic shift of the fluorescence and a decrease in the quantum yield to ca. 0.4. The DSB derivatives and the related segmented PPV derivatives show nearly the same absorption spectra, fluorescence spectra, and radiative rate constantsk _f= Φ_f/Τ, indicating the efficacy of the segmentation of the polymer chain. The radiative rate constants determined by the Φ_f and Τ values and by the Strickler/Berg formula are in reasonable agreement. This supports the possibility of interpreting the properties of the polymers in terms of their DSB units. The decrease in the emission anisotropy can be ascribed to multistep energy transfer processes between different oriented segments.     

Spectral-luminsecent properties of polyalkanesteramides

Absorption and fluorescence spectra and fluorescence quantum yields of solutions and transparent films of polyalkanesterimides (PAEI) were studied. The molecular chain of the investigated polyalkanesterimides contains phthalimide repeating units and –(CH₂)_n– fragments where n = 6 and 10. It is shown that the fluorescent properties of such polymers are the same as those of low-molecular-weight phthalimide luminophores. The alkane fragments contained in the polymer chain have been concluded to prohibit a charge-transfer transition and thereby enhance the polyalkanesterimide fluorescence intensity.     

A Molecular Thermometer Based on the Delayed Fluorescence of C70 Dispersed in a Polystyrene Film

A new optical molecular thermometer, based on the thermally activated delayed fluorescence of C₇₀ dispersed in a polystyrene film, was developed. In the presence of oxygen, the fluorescence intensity of the C₇₀ film is essentially temperature independent in a wide range. In the absence of oxygen, however, the fluorescence intensity markedly increases with temperature. At room temperature (25°C), and after degassing the sample, the fluorescence intensity of C₇₀ increases 22 times, while at 100°C the fluorescence intensity is increased by 70 times. With our system, the very weak fluorescence of C₇₀ (Φ_F ≅ 5 × 10⁻⁴, in toluene) can be increased up to 91 times (up to an estimated maximum value Φ_F = 0.046). The estimate value of the singlet-triplet gap (29 kJ mol⁻¹) and the fluorescence lifetime (0.63 ns) of the C₇₀ in film are in agreement with the values reported in the literature for C₇₀ in solution. The values of the phosphorescence lifetime at room temperature (23 ms) and the quantum yield of triplet formation (0.989) were also determined. The system is completely reversible with respect to heating-cooling cycles.     

Synthesis,Electrochemical, and Optical Properties of New Fluorescent,Substituted Thieno[3,2-b][1]Benzothiophenes

The synthesis, electrochemical and optical properties of three fluorescent substituted thieno[3,2-b][1]benzothiophenes (TBT) derivatives, including 3-methoxythieno[3,2-b][1]benzothiophene (3-MeO-TBT), 2,3-dimethylthieno[3,2-b][1]benzothiophene (2,3-diMe-TBT), and 6-methoxythieno[3,2-b][1]benzothiophene-2-carboxylate (6-MeO-TBT-2-COOMe), were investigated. The oxidation potential values varied between 1.40 and 1.20 V/SCE according to the electronic substituent effect, and electropolymerization attempts, performed in 0.1 M LiClO₄ acetonitrile solution, led to the formation of very thin films of poly(3-MeO-TBT) and poly(2,3-di-Me-TBT). Electronic absorption spectra, fluorescence excitation and emission spectra, fluorescence quantum yields (Φ_F) , lifetimes (τ_F), and other photophysical parameters of the three new TBT derivatives were measured in DMSO solutions at room temperature. For the methyl-and methoxy-substituted TBT derivatives, the fluorescence emission peak were slightly red shifted relative to that of unsubstituted TBT (Δλ_em = 1–12 nm) whereas, in the case of 6-MeO-TBT-2-COOMe, a rather strong red-shift (Δλ_em = 73 nm) was attributed to the existence of a “push-pull” electronic interaction of the MeO and COOMe groups. All Φ_F values were rather high, varying between 0.11 and 0.35, according to the substituent effect. Fluorescence decays were mono-exponential and τ_F values were very short, ranging between 0.11 and 0.30 ns for the substituted TBT derivatives until study.     

Fluorescence Properties of Dibenzofluorescein in Aqueous Solution

The deprotonation of dibenzofluorescein (DBFL), a long wavelength fluorescence probe, results in the simultaneous occurrence of neutral form, monoanion and dianion under physiological conditions. The fluorescence properties of the former two cannot be measured directly because they are always coexistent with some other species. By measuring the fluorescence under various pHs we computed the fluorescence parameters for each species involved in the prototropic equilibria of DBFL, including each species’ emission spectrum, excitation spectrum, emission and excitation maximum, fluorescence quantum yield and lifetime. It was found that the monoanion is the most fluorescent chromospheres (Φ _f = 0.66, compared to Φ _f = 0.25 for dianion, 0.18 for cation and 0.0 for the neutral form). Together with the computed pK _as, we are able to suggest that the monoanion plays a major role under physiological conditions when DBFL is used as a fluorescence probe, contrary to the assumption in literature.     

Synthesis and Characterization of New Fluorene-Based Singlet Oxygen Sensitizers

The synthesis, photophysical characterization, and determination of singlet oxygen quantum yields (Φ_Δ) for a class of fluorene derivatives with potential application in two-photon photodynamic therapy (PDT) is reported. It has been demonstrated that these compounds possess the ability to generate singlet oxygen (¹O₂) upon excitation. A photochemical method, using 1,3-diphenylisobenzofuran (DPBF) as ¹O₂ chemical quencher, was employed to determine the singlet oxygen quantum yields (Φ_Δ) of the fluorene-based photosensitizers in ethanol. Φ_Δ values ranged from 0.35 to 0.75. These derivatives may have potential application as two-photon photosensitizers when pumped via two-photon excitation in the near-IR spectral region.     

Novel Fluorophores as Building Blocks for Optical Probes for In Vivo Near Infrared Fluorescence (NIRF) Imaging

Aiming at the identification of new fluorescent reporters for targeted optical probes, we assessed the application-relevant features of a novel asymmetric cyanine, DY-681, in comparison to the only clinically approved dye indocyanine green (ICG), the golden imaging standard Cy5.5, and the asymmetric cyanine DY-676 successfully exploited by us for the design of different contrast agents. This comparison included the analysis of the spectroscopic properties of the free fluorophores and their thermal stability in aqueous solution as well as their cytotoxic potential. In addition, the absorption and emission features of IgG-conjugated DY-681 were examined. The trimethine DY-681 exhibited spectral features closely resembling that of the pentamethine Cy5.5. Its high thermal stability in phosphate buffer saline (PBS) solution in conjunction with its low cytotoxicity, reaching similar values as determined for Cy5.5 and DY-676, renders this dye more attractive as ICG and, due to its improved fluorescence quantum yield in PBS, also superior to DY-676. Although in PBS, Cy5.5 was still more fluorescent, the fluorescence quantum yields (Φ _f) of DY-681 and Cy5.5 in PBS containing 5 mass-% bovine serum albumin (BSA) were comparable. Labeling experiments with DY-681 and the model antibody IgG revealed promisingly high Φ _f values of the bioconjugated dye.     

Luminescence of oxotetrahydrobenzo[c]phenanthridine in polar and nonpolar solvents: Inversion of the energy levels of the Sππ* and Tnπ* states

The spectral-luminescent properties and electronic-level structure of a derivative of oxotetrahydrobenzo[c]phenanthridine—3,3-dimethyl-1,2,3,4-tetrahydrobenzo[c]phenanthridine-1-one (DTP)—in polar and nonpolar solutions are studied by the luminescence and picosecond spectroscopy techniques at 293 and 77 K. It is shown that DTP exhibits ππp* fluorescence only in polar proton-containing methanol, ethanol, and n-propanol and that this fluorescence is associated with a chromophore + alcohol complex. Solutions of DTP in n-propanol and the nonpolar mixture methylcyclohexane + toluene (6:1) at 77 K display ππp* phosphorescence with a quantum yield Φ_Ph=0.1, a lifetime τ_Ph=1.9 s, and a frequency of the 0-0 transition equal to 21550 cm⁻¹. The fact that DTP fluorescence is absent in aprotic solvents and exists in alcohols is explained by the inversion of the energy levels of the S _ππ* and T _n π* states, as a result of which the energy level of the fluorescing S _ππ* state in alcohol becomes the lowest. The picosecond spectra and kinetics of the inducedS _n (ππ*) ← S ₁(π π*) and T _k (ππ*) ← T ₁(ππ*) absorption made it possible to estimate the lifetime of the S ₁(ππ*) state of DTP in n-propanol at 293 K (20±10 ps) and the position of the triplet-triplet absorption peak (495 nm). __________ Translated from Optika i Spektroskopiya, Vol. 94, No. 6, 2003, pp. 993–998. Original Russian Text Copyright ? 2003 by Bondarev, Knyukshto, Tikhomirov, Pyrko.     

Quantized magnetic flux through the ground-state orbit of the hydrogen atom

We have investigated the spin-dependent quantized magnetic fluxes through the ground-state electronic orbit of the hydrogen atom. We show that the corresponding fluxes are (1/2)Φ₀ for the spin-up case and (3/2)Φ ₀ for the spin-down case, respectively, where Φ₀ = hc/e is the flux quantum. Using the energy-flux proportionality, we also show that the spin-up case (where the electron spin is antiparallel to the proton spin, resulting in zero total spin) is the spin-dependent ground state of the hydrogen atom. The present result helps to understand the spin flip-flop in excitonic transitions in nanostructures.     

Multiple-quantum radio-frequency spectroscopy of atoms: Application to the metrology of geomagnetic fields

The evolution of the radio-frequency magnetic resonance spectrum of optically oriented potassium atoms in terrestrial magnetic fields as a function of the amplitude of the alternating magnetic field H ₁ is investigated theoretically and experimentally. It is shown that among the set of observed n-quantum resonances which satisfy the selection rules ΔF=0 and Δm _F±n (n is an integer), there is one resonance with the highest multiplicity n=4 (m _F=2⇔m _F=−2), which has exceptional properties. These qualities make this resonance a candidate for use in a weak-field quantum magnetometer with record-high characteristics. A preliminary investigation of an experimental model of a four-quantum potassium magnetometer is performed. Zh. Tekh. Fiz. 69, 27–30 (September 1999)     

Energy and pressure dependence of the CO2 laser induced dissociation of sulfur hexafluoride

Low pressure SF₆ with its isotopes in natural abundance was irradiated by a pulsed CO₂ laser operated on theP20 line (10.6 μm band). Dissociation yields of³²SF₆ and³⁴SF₆ were measured separately. If the radiation is focussed into the cell, the dissociation yield is proportional to the 3/2 power of the laser energy, as was derived under general conditions and confirmed experimentally. The reaction probabilityP(Φ), the fraction of molecules dissociated by an energy flux Φ, was measured using parallel light. For both isotopes,P(Φ) saturates at high energy flux close toP=1. At a lower flux (2 J cm⁻²), the dissociation probability of³²SF₆ displays a threshold, whereas the dissociation probability of³⁴SF₆ is a very steep function of Φ over the whole range of fluxes.P(Φ) at the higher energy flux was measured in a cavity absorption cell, in which up to 80% of the molecules were dissociated by a single pulse. Below 0.2 mbar SF₆ the dissociation yields for both isotopes are pressure independent. Above 2 mbar the isotopic selectivity is completely lost. Addition of hydrogen always decreases the dissociation yields.     

Fluorescence Studies on Potential Antitumoral Heteroaryl and Heteroannulated Indoles in Solution and in Lipid Membranes

Fluorescence properties of three potential antitumoral compounds, a 3-(dibenzothien-4-yl)indole 1, a phenylbenzothienoindole 2 and a 3-(dibenzofur-4-yl)indole 3, were studied in solution and in lipid aggregates of dipalmitoyl phosphatidylcholine (DPPC), dioleoyl phosphatidylethanolamine (DOPE) and egg yolk phosphatidylcholine (Egg-PC). The 3-(dibenzofur-4-yl)indole 3 exhibits the higher fluorescence quantum yields in all solvents studied (0.32 ≤ Φ_F ≤ 0.51). All the compounds present a solvent sensitive emission, with significant red shifts in alcohols. The results point to an ICT character of the excited state, more pronounced for compound 1. Fluorescence (steady-state) anisotropy measurements of the compounds incorporated in lipid aggregates of DPPC, DOPE and Egg-PC indicate that the three compounds are deeply located in the lipid bilayer, feeling the difference between the rigid gel phase and fluid phases.     

Dynamical correlations of two-dimensional vortex-like defects

High-order dynamical correlations of defects (quantum vortices, disclinations, etc.) in thin films are examined by starting from the Langevin equation for the defect motion. It is demonstrated that the dynamical correlation functions F _2n of the vorticity or disclinicity behave as F _2n ∼y ²/r ⁴ⁿ , where r is the characteristic scale and y is the renormalized fugacity. Therefore below the Berezinskii-Kosterlitz-Thouless transition temperature the F _2n are characterized by anomalous scaling exponents. The behavior differs strongly from the normal law F _2n ∼F ₂ ⁿ obeyed by equal-time correlation functions; the unequal-time correlation functions appear to be much larger. The phenomenon resembles intermittency in turbulence. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 675–679 (25 November 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Acidichromism and Ionochromism of Luteolin and Apigenin,the Main Components of the Naturally Occurring Yellow Weld: A Spectrophotometric and Fluorimetric Study

Luteolin and apigenin, extracted from Reseda luteola L., were spectrophotometrically and fluorimetrically studied. The spectra were investigated as a function of pH in methanol/water solutions (1/2, v/v) in the 2–12 pH range. The absorption spectra markedly shifted to the red by increasing the pH. Three acid–base dissociation steps were detected for luteolin (pK _a = 6.9; 8.6; 10.3) and two for apigenin (pK _a = 6.6; 9.3). Fluorescence emission was very weak or undetectable (Φ _F < 10⁻⁴) in acidic solution, but increased in intensity with increasing the pH. Both molecules exhibited a great propensity towards complex formation with metal ions, with association constants on the order of 10⁵–10⁷ for the first complexation step; in the presence of excess Al³⁺ ions, multiple equilibria were detected. A marked fluorescence enhancement was observed upon complexation with Al³⁺ ions (Φ _F ∼ 1 for luteolin and ∼10⁻² for apigenin).     

Stress-Induced Alteration of Chlorophyll Fluorescence Polarization and Spectrum in Leaves of <Emphasis Type="Italic">Alocasia macrorrhiza</Emphasis> L. Schott

The value of intrinsic chlorophyll fluorescence polarization, and the intensity in emission spectrum were investigated in leaf segments of Alocasia macrorrhiza under several stress conditions including different temperatures (25–50°C), various concentrations of NaCl (0–250 mM), methyl viologen (MV, 0–25 μM), SDS (0–1.0%) and NaHSO₃ (0–80 μM). Fluorescence emission spectrum of leaves at wavelength regions of 500–800 nm was monitored by excitation at 436 nm. The value of fluorescence polarization (P value), as result of energy transfer and mutual orientation between chlorophyll molecules, was determined by excitation at 436 nm and emission at 685 nm. The results showed that elevated temperature and concentrations of salt (NaCl), photooxidant (MV), surfactant (SDS) and simulated SO₂ (NaHSO₃) treatments all induced a reduction of fluorescence polarization to various degrees. However, alteration of the fluorescence spectrum and emission intensity of F₆₈₅ and F₇₃₁ depended on the individual treatment. Increase in temperature and concentration of NaHSO₃ enhanced fluorescence intensity mainly at F₆₈₅, while an increase in MV concentration led to a decrease at both F₆₈₅ and F₇₃₁. On the contrary, NaCl and SDS did not cause remarkable change in fluorescence spectrum. Among different treatments, the negative correlation between polarization and fluorescence intensity was found with NaHSO₃ treatments only. We concluded that P value being measured with intrinsic chlorophyll fluorescence as probe in leaves is a susceptible indicator responding to changes in environmental conditions. The alteration of P value and fluorescence intensity might not always be shown a functional relation pattern. The possible reasons of differed response to various treatments were discussed.     

Fluorescence and Electronic Structure of the Laser Dye DCM in Solutions and in Polymethylmethacrylate

The photophysical properties and polarization of the fluorescence of the laser dye 4-dicyanomethylene-2-methyl-6-(p(dimethylamino)styryl)-4H-pyran (DCM) in solutions of different polarities and in polymethylmethacrylate (PMMA) at 293 and 77 K were investigated by stationary and pulsed fluorescent spectroscopy. Based on the data of polarized fluorescence, an oscillator model has been suggested, according to which the electronic absorption spectrum of DCM in the 240–500-nm range is formed by at least three electron transitions. The quantum yield of fluorescence _f increases linearly with increase in the polarity of a solvent in a toluene dimethylsulfoxide (DMSO) mixture from 0.08 (toluene) to 0.80 (DMSO). An increase of _f to 0.90 was also observed on increase in the rigidity of the medium by freezing a solution of DCM in n-propanol at 77 K or introducing of a dye to the polymeric matrix of PMMA at room temperature ( _f = 0.76). The fluorescence-decay kinetics of DCM in toluene, n-propanol, and PMMA at 293 K follows a biexponential law, whereas in n-hexane and vaseline oil at 293 K and in n-propanol at 77 K it follows a monoexponential law. The mechanisms underlying radiationless deactivation of the electron-excitation energy in solutions and in polymeric media are discussed.     

Cooper pairing and superfluidity in the Emery model

The energy E of the system as a function of the gauge phase Φ is calculated by exact diagonalization in a two-dimensional Cu₄O₈ cluster and by the slave-boson method for large systems. It is shown that motion of carriers with charge 2e, i.e., Cooper pairs, is observed for certain values of the parameters in the Hamiltonian. This motion is identified from the onset of a characteristic maximum of E(Φ) at Φ≈Φ₀/2, where Φ₀ is the flux quantum. The phase diagram is constructed and the range of values of the model parameters where the effect is observed is determined. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 78–82 (25 January 1996)     

Improved condition for the absence of bound states and converging analytic bounds to critical screening parameter

Converging lower bound to the critical screening parameterD _c associated with the ground state of a two-particle system interacting through a cut-off Coulomb potential is obtained analytically using an improved condition for the absence of bound states. The predicted numerical result for the lower bound is found to be within 10⁻³% of the exact result. On the other hand, a multi-parameter variational approach yields a tight upper bound, within 0.54% of the exact result. It is shown that the critical screening parameter for the exciteds-states can also be determined in an approximate way. We obtainD _c ^ms ≈ [0.764435n ⁻²+0.617737n ⁻³]⁻¹ wheren is the principal quantum number. The predictedD _c for various quantum states (n=1 to 8) are in good agreement with the values obtained numerically by Singh and Varshni.