Electronic Energy Transfer in a Single Donor–Acceptor Pair with Triplet–Triplet Absorption

Optics and Spectroscopy - The protocol of dynamic decoupling using a sequence of resonance RF pulses with different shapes in a system of dipole-coupled electron/nuclear spins with inhomogeneous...     

Spin Chemistry Investigation of Peculiarities of Photoinduced Electron Transfer in Donor–Acceptor Linked System

Photoinduced intramolecular electron transfer in linked systems, (R,S)- and (S,S)-naproxen-N-methylpyrrolidine dyads, has been studied by means of spin chemistry methods [magnetic field effect and chemically induced dynamic nuclear polarization (CIDNP)]. The relative yield of the triplet state of the dyads in different magnetic field has been measured, and dependences of the high-field CIDNP of the N-methylpyrrolidine fragment on solvent polarity have been investigated. However, both (S,S)- and (R,S)-enantiomers demonstrate almost identical CIDNP effects for the entire range of polarity. It has been demonstrated that the main peculiarities of photoprocesses in this linked system are connected with the participation of singlet exciplex alongside with photoinduced intramolecular electron transfer in chromophore excited state quenching.     

Light-Induced Spin Polarization in Porphyrin-Based Donor–Acceptor Dyads and Triads

The light-induced spin polarization generated by sequential electron transfer in an axially bound triad based on Al(III) porphyrin (AlPor) is discussed. In the triad, $\text {TTF} \!-\! \text {Ph} \!-\! \text {py}\!\to\!\text {AlPor}\! - \!\text {Ph}\! -\! \text {NDI}$ , the electron acceptor naphthalene diimide (NDI) is attached covalently to the Al(III) center, while the donor tetrathiafulvalene (TTF) coordinates to Al(III) via an appended pyridine (py) on the opposite face of the porphyrin ring. Excitation of the porphyrin at room temperature in solution leads to charge separation between the donor and acceptor. In the liquid crystalline solvent 5CB, a spin-polarized transient electron paramagnetic resonance spectrum of a weakly coupled radical pair is observed and is assigned to the state $ \text{TTF}^{\cdot + } \text{NDI}^{\cdot - } $ . In the absence of the donor, a spectrum of the triplet state of the strongly coupled radical pair $ \text{AlPor}^{ \cdot + } \text{NDI}^{ \cdot - } $ is obtained. The analysis of the spectra is described using a model developed by Kandrashkin et al. (Appl Magn Reson 15: 417–447, 1998). It is shown that in the triad the spectrum of $ \text {TTF}^{ \cdot + } \text {NDI}^{ \cdot - } $ shows evidence of the singlet–triplet mixing in the precursor $ \text{AlPor}^{ \cdot + } \text{NDI}^{ \cdot - } $ . At later time, singlet recombination leads to inversion of the spectrum, from which the singlet back reaction lifetime is estimated as 350 ns. The decay of the inverted spectrum yields a lifetime of 8.3 μs for the triplet back reaction lifetime.     

CT-Operated Bifunctional Fluorescent Probe Based on a Pretwisted Donor–Donor–Biphenyl

Taking into account the structural requirements for TICT-type sensor molecules, a general synthetic route to derive pH and cation-responsive pretwisted donor (D)–donor (D) biphenyls (b) equipped with donor receptors is developed and a first model compound containing a mono aza-15-crown-5 and a DMA receptor is synthesized, see Scheme 1. The spectroscopic properties of this new bifunctional D–D biphenyl are studied in the non-polar and polar solvents cyclohexane, acetonitrile, and methanol. Protonation as well as complexation studies are performed with the representative metal ions Na(I), K(I), Ca(II), Ag(I), Zn(II), Cd(II), Hg(II), and Pb(II) to reveal the potential of this molecule for communication of whether none, only one, or both binding sites are engaged in analyte coordination by spectroscopically distinguishable outputs. The results are compared to those obtained with closely related donor (D)–acceptor (A) substituted biphenyl-type sensor molecules and are discussed within the framework of neutral and ionic D – A biphenyls.     

Triplet‐Triplet Electron Excitation Energy Transfer in the Gas Phase for the Carbazol–Diacetyl Donor‐Acceptor Pair

For the carbazol–diacetyl donoracceptor pair, the features of exothermal triplettriplet (TT) transfer of electron excitation energy in the gas phase upon excitation of carbazol by the nitrogen laser radiation which is not absorbed by diacetyl have been investigated. The luminescence spectra of carbazol in the gas phase have been studied. It is shown that carbazol phosphorescence in the gas phase is absent. Therefore, for estimating the TT transfer efficiency and its temperature dependence, in the kinetic approximation the dependences of the intensity of timeresolved delayed fluorescence of carbazol and sensitized phosphorescence of diacetyl on diacetyl pressure have been analyzed. It has been found that in the gas phase the features of the electronic structure of the molecules under investigation are responsible for the low efficiency of transfer (2·10^–4 at 453 K), which increases by an order of magnitude with increasing temperature in the 453–513 K range despite the increasing influence of the back transfer.     

Determination of the Efficiency and Energy Transfer Rate in the Fluorescence of a Single Donor–Acceptor Pair Attached to a Biomolecule

Resonance energy transfer from a single donor molecule to a single acceptor molecule (Förster resonance energy transfer) is currently used to determine the microscopic parameters describing interconformational changes in a protein molecule to which this single donor–acceptor pair is attached. A recently developed method makes it possible to intricately search for such parameters using a formula for the efficiency of Förster resonance energy transfer, which is the sum of several Gaussians. Another simpler method for the determination of the desired parameters of interconformational transitions has been proposed in this work on the basis of statistical processing of fluctuating tracks of fluorescence of a single donor–acceptor pair attached to a protein molecule.     

Pressure-Induced Metallization Accompanied by Elongated S–S Dimer in Charge Transfer Insulator NiS_2

The insulator-metal transition triggered by pressure in charge transfer insulator NiS2 is investigated by combining high-pressure electrical transport,synchrotron x-ray diffraction and Raman spectroscopy measurements up to40-50 GPa.Upon compression,we show that the metallization firstly appears in the low temperature region at～3.2 GPa and then extends to room temperature at～8.0 GPa.During the insulator-metal transition,the bond length of S-S dimer extracted from the synchrotron x-ray diffraction increases with pressure,which is supported by the observation of abnormal red-shift of the Raman modes between 3.2 and 7.1 GPa.Considering the decreasing bonding-antibonding splitting due to the expansion of S-S dimer,the charge gap between the S-ppπ* band and the upper Hubbard band of Ni-3 d eg state is remarkabl.y decreased.These results consistently indicate that the elongated S-S dimer plays a predominant role in the insulator-metal transition under high pressure,even though the p-d hybridization is enhanced simultaneously,in accordance with a scenario of charge-gap-controlled type.     

Mechanisms of Fluorescence Quenching in Donor—Acceptor Labeled Antibody—Antigen Conjugates

The cyanine dyes Cy5 and Cy5.5 are presented as a new long wavelength-excitable donor-acceptor dye pair for homogeneous fluoroimmunoassays. The deactivation pathways responsible for the quenching of the fluorescence of the antibody-bound donor are elucidated. Upon binding of the donor dye to the antibodies at low dye/protein ratios, its fluorescence quantum yield rises to unity. Higher dye/protein ratios lead to progressive aggregation of the dyes, which results in quenching of monomer fluorescence due to resonance energy transfer (RET) from the monomers to the nonfluorescent dimers. The dependence of the quenching efficiency on the labeling ratio is described quantitatively by assuming a Poisson distribution of the dyes over the antibodies. The maximum fluorescence intensity per antibody is obtained at a labeling ratio of 4. Upon formation of the antibody-antigen complex, electron transfer and RET to the antigen-bound acceptor dye occur. Steady-state and time-resolved fluorescence measurements reveal that approximately 50% of the donor quenching is due to RET, while the residual quenching effect is caused by the static quenching process.     

Luminescence of Donor‐Acceptor Pairs in Compounds of Yttrium and Scandium Oxides

The luminescence spectra of Sc₂O₃, Y₂O₃, and Y₂GeO₅ ceramics and thin films exposed to laser and cathode excitation were investigated. The investigation of the properties of longwave luminescence bands in Sc₂O₃ with maxima at 2.65, 2.35, and 2.05 eV, in Y₂O₃ with maxima at 2.60, 2.35, and 2.10 eV, and also in Y₂GeO₅ with maxima at 2.55, 2.25, and 2.00 eV point to the fact that they are caused by radiative recombination of the excited donoracceptor pairs Sc³⁺ (or Y³⁺)O^2–.     

Proton Halo or Skin in the Excited States of Light Nuclei

Properties of nuclei 13,15,N and 9B are investigated in the relativistic mean-field theory with NLz and NL3 force parameters.The calculated binding energies are very close to the experimental ones.The calculations show that the first excited state (1p1/2) in 9B,the first excited state (2s1/2)in 13 N and the second excited state(2s1/2) in 15N are weakly bound .In particular,for 13N and 15N,the proton density distributions in the two above excited states have a long tail and the rms radii of the last proton are greatly larger compared with their respective matter radii.It is predicted that a proton halo exists in the first excited state of 13N and in the second excited state of 15N,respectively.It also indicates that the first excited state in 9B is a proton skin state.     

Isolated (Quantum) Emitters Generated with the Participation of Donor–Acceptor Pairs in the ZnSe/ZnMgSSe Heterostructure

Measurements of low-temperature (5 K) microphotoluminescence reveal the existence of isolated (quantum) emitters in ZnSe/ZnMgSSe quantum well with a radiation line experiencing abrupt displacements of its spectral position by several meV within 1–10 min. The unusual properties of the detected emitters are explained on the basis of a system with a large dipole moment in its ground state, e.g., a single donor–acceptor pair.     

Organic Light Emitting Diodes with an Organic Acceptor/Donor Interface Involved in Hole Injection

Organic light emitting diodes with an interface of organic acceptor 3-, 4-, 9-,10-perylenetetracarboxylic dianhydride （PTCDA） and donor copper phthalocyanine （CuPc） involved in hole injection are fabricated. As compared to the conventional device using a 5 nm CuPc hole injection layer, the device using an interface of 10nm PTCDA and 5 nm CuPc layers shows much lower operating voltage with an increase of about 46% in the maximum power efficiency. The enhanced device performance is attributed to the efficient hole generation at the PTCDA/CuPc interface. This study provides a new way of designing hole injection.     

The 17th International Conference on Dynamical Process in Excited States of Solids

<正>We are pleased to announce that DPC'10 will be held June 20～25,2010 at Argonne National Laboratory,Argonne,IL,USA.Website:http://dpc10.cse.anl.gov Scope     

Excited States in ^18Ne Studied via ^17F＋p

The elastic resonance scattering of ^17F＋p is studied in inverse kinematics via a thick-target method. The excitation function for ^17F＋p elastic scattering is obtained within the energy interval of Ec.m ≈ 0.4-1.7 MeV. The experimental excitation function is analyzed with a multilevel R-matrix code MULTI7, and the proton widths are deduced. The α decay from 6.15 MeV 1- state in 18Ne is observed, which is critical to the 14O（α, p）17F reaction as the main breakout route from CNO cycle to rp-process in supernovae and x-ray bursts.     

On the Quantitative Treatment of Donor–Donor Energy Migration in Regularly Aggregated Proteins

An algorithm is presented that quantitatively accounts for donor–donor energy migration (DDEM) among fluorophore-labeled proteins forming regular aggregates. The DDEM algorithm is based on Monte Carlo and Brownian dynamics simulations and applies to calculation of fluorescence depolarisation data, such as the fluorescence anisotropy. Thereby local orientations, as well as reorienting motions of the fluorescent group are considered in the absence and presence of DDEM and among, in principle, infinitely many proteins as they form regular aggregates. Here we apply the algorithm for calculating and illustrating the DDEM and the time-resolved fluorescence anisotropy under static as well as dynamic conditions within helical, linear and circular aggregate structures. A principal approach of the DDEM algorithm for analysing protein aggregates is also outlined.     

Mechanism of Intramolecular Transfer of a Proton and an Electron in an Excited State of 4′‐Amine Derivatives of 3‐Hydroxyflavone

The intramolecular transfer of a proton in 4amine derivatives of 3hydroxyflavone was investigated in binary solvents, which are a mixture of polar and nonpolar liquids. The dependence of the efficiency of the intramolecular transfer of a proton in an excited state on the frequency of the exciting light has been revealed, which is due to the spectral inhomogeneity of the molecules of fluorophors in binary solvents. A scheme of the processes of intramolecular transfer of a proton and an electron in 4amine derivatives of 3hydroxyflavone is suggested.     

Energy and Charge Transfer from Guest to Host in Doped Organic Electroluminescent Devices

The luminescence properties of doped organic electroluminescent devices are explained by means of a Hamiltonian model.The results show that there is a corresponding relation between the amount of transferred charge and the change of the energy originating from charge transfer,and the relation can be influenced by dopant concentration.As the amountof transferred charge increases,the total energy decreases and the luminescence intensity increases.Therefore,we deduce that the energy transfer from guest to host may be derived from the charge transfer.For a given organic electroluminescent device,the maximum value of the conductivity can be observed in a specific dopant concentration.The calculated results show that the greater the transferred charges,the higher the conductivities in doped organic electroluminescent devices.The results agree basically with experimental results.     

Neutron Halos in the Excited States of Spherical Nuclei Near the β-Stable Line

The newly discovered neutron halos in the excited states of nuclei 12B, 13C, and 209pb are studied by therelativistic mean-field theory. The calculated binding energies are very close to the experimental ones. The experimentally extracted root-mean-square radii of the last neutron with different occupations in nuclei are well reproduced bycalculations. New candidates for the neutron halos in excited states are predicted and are useful for further search ofneutron halos in the excited states of stable nuclei.