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Decay Channel (decay + channel)
Selected AbstractsEnergy- and Charge-Transfer Processes in a Perylene,BODIPY,Pyridine Tripartite ArrayEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2008Mohammed A. H. Alamiry Abstract A novel boron dipyrromethene (BODIPY) dye has been synthesized in which the F atoms, usually bound to the boron center, have been replaced with 1-ethynylperylene units and a 4-pyridine residue is attached at the meso -position. The perylene units function as photon collectors over the wavelength range from 350 to 480 nm. Despite an unfavorable spectral overlap integral, rapid energy transfer takes place from the singlet-excited state of the perylene unit to the adjacent BODIPY residue, which is itself strongly fluorescent. The mean energy-transfer time is 7,±,2 ps at room temperature. The dominant mechanism for the energy-transfer process is Dexter-type electron exchange, with Förster-type dipole,dipole interactions accounting for less than 10,% of the total transfer probability. There are no indications for light-induced electron transfer in this system, although there is evidence for a nonradiative decay channel not normally seen for F -type BODIPY dyes. This new escape route is further exposed by the application of high pressure. The meso -pyridine group is a passive bystander until protons are added to the system. Then, protonation of the pyridine N atom leads to complete extinction of fluorescence from the BODIPY dye and slight recovery of fluorescence from the perylene units. Quenching of BODIPY-based fluorescence is due to charge-transfer to the pyridinium unit whereas the re-appearance of perylene-based emission is caused by a reduction in the Förster overlap integral upon protonation. Other cations, most notably zinc(II) ions, bind to the pyridine N-atom and induce similar effects but the resultant conjugate is weakly fluorescent.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] The N -Arylamino Conjugation Effect in the Photochemistry of Fluorescent Protein Chromophores and AminostilbenesCHEMISTRY - AN ASIAN JOURNAL, Issue 9 2010Guan-Jhih Huang Abstract To understand the nonradiative decay mechanism of fluorescent protein chromophores in solutions, a systematic comparison of a series of (Z)-4-(N -arylamino)benzylidene-2,3-imidazolinones (ABDIs: 2,P, 2,PP, 2,OM, and 2,OMB) and the corresponding trans -4-(N -arylamino)-4,-cyanostilbenes (ACSs: 1,P, 1,PP, 1,OM, and 1,OMB) was performed. We have previously shown that the parameter ,f+2,,tc, in which ,f and ,tc are the quantum yields of fluorescence and trans,cis photoisomerization, respectively, is an effective probe for evaluating the contribution of twisted intramolecular charge transfer (TICT) states in the excited decays of trans -aminostilbenes, including the push,pull ACSs. One of the criteria for postulating the presence of a TICT state is ,f+2,,tc,1.0, because its formation is decoupled with the CC bond (,) torsion pathway and its decay is generally nonradiative. Our results show that the same concept also applies to ABDIs 2 with the parameter ,f+2,,ZE in which ,ZE is the quantum yield of Z,E photoisomerization. We conclude that the , torsion rather than the CC bond (,) torsion is responsible for the nonradiative decays of ABDIs 2 in aprotic solvents (hexane, THF, acetonitrile). The phenyl-arylamino CN bond (,) torsion that leads to a nonradiative TICT state is important only for 2,OM in THF and acetonitrile. If the solvent is protic (methanol and 10,20,% H2O in THF), a new nonradiative decay channel is present for ABDIs 2, but not for ACSs 1. It is attributed to internal conversion (IC) induced by solvent (donor),solute (acceptor) hydrogen-bonding (HB) interactions. The possible HB modes and the concept of , torsion-coupled proton transfer are also discussed. [source] Mass and lifetime measurements of exotic nuclei in storage ringsMASS SPECTROMETRY REVIEWS, Issue 5 2008Bernhard Franzke Abstract Mass and lifetime measurements lead to the discovery and understanding of basic properties of matter. The isotopic nature of the chemical elements, nuclear binding, and the location and strength of nuclear shells are the most outstanding examples leading to the development of the first nuclear models. More recent are the discoveries of new structures of nuclides far from the valley of stability. A new generation of direct mass measurements which allows the exploration of extended areas of the nuclear mass surface with high accuracy has been opened up with the combination of the Experimental Storage Ring ESR and the FRragment Separator FRS at GSI Darmstadt. In-flight separated nuclei are stored in the ring. Their masses are directly determined from the revolution frequency. Dependent on the half-life two complementary methods are applied. Schottky Mass Spectrometry SMS relies on the measurement of the revolution frequency of electron cooled stored ions. The cooling time determines the lower half-life limit to the order of seconds. For Isochronous Mass Spectrometry IMS the ring is operated in an isochronous ion-optical mode. The revolution frequency of the individual ions coasting in the ring is measured using a time-of-flight method. Nuclides with lifetimes down to microseconds become accessible. With SMS masses of several hundreds nuclides have been measured simultaneously with an accuracy in the 2,×,10,7 -range. This high accuracy and the ability to study large areas of the mass surface are ideal tools to discover new nuclear structure properties and to guide improvements for theoretical mass models. In addition, nuclear half-lives of stored bare and highly charged ions have been measured. This new experimental development is a significant progress since nuclear decay characteristics are mostly known for neutral atoms. For bare and highly charged ions new nuclear decay modes become possible, such as bound-state beta decay. Dramatic changes in the nuclear lifetime have been observed in highly charged ions compared to neutral atoms due to blocking of nuclear decay channels caused by the modified atomic interaction. High ionization degrees prevail in hot stellar matter and thus these experiments have great relevance for the understanding of the synthesis of elements in the universe and astrophysical scenarios in general. © 2008 Wiley Periodicals, Inc., Mass Spec Rev 27: 428,469, 2008 [source] Experimental Ti i oscillator strengths and their application to cool star analysisMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006R. J. Blackwell-Whitehead ABSTRACT We report experimental oscillator strengths for 88 Ti i transitions covering the wavelength range 465,3892 nm, 67 of which had no previous experimental values. Radiative lifetimes for 13 energy levels, including the low energy levels 3d2(3F) 4s4p (3P) z 5D°j, have been measured using time-resolved laser-induced fluorescence. Intensity-calibrated Ti i spectra have been measured using Fourier transform spectroscopy to determine branching fractions for the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region , > 1.0 ,m, a region of particular interest to the analysis of cool stars and brown dwarfs. [source] | ||||||||||