Home About us Contact
|
Home About us Contact | ||
|
|
||
Internal Conversion (internal + conversion)
Selected AbstractsEffect of the Media on the Quantum Yield of Singlet Oxygen (O2(1,g)) Production by 9H -Fluoren-9-one: Solvents and Solvent MixturesHELVETICA CHIMICA ACTA, Issue 2 2003Claudia We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O2(1,g), denoted as 1O2) by 9H -fluoren-9-one (FLU). The normalized empirical parameter E derived from ET(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of 1O2 production (,,) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (,ISC). Values of ,, of unity have been found in alkanes. In nonprotic solvents of increasing polarity, ,ISC and, therefore, ,, decrease due to solvent-induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor 1O2 sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing ,, to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of ,, upon addition of increasing amounts of the latter. [source] Hurricane potential intensity from an energetics point of viewTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 602 2004Weixing Shen Abstract This article describes an approach to hurricane potential intensity with a model that considers total kinetic energy balance within a hurricane. The major kinetic energy source and sink are the kinetic energy converted from sea surface entropy flux and the surface dissipation, respectively, but the conversion efficiency is radius-dependent in this model. Also, the internal conversion due to convectively available potential energy (CAPE) as a source is considered. In contrast to previous potential intensity models, energy balance in the entire hurricane is used to get its steady state. With this model, the roles of environmental sea surface temperature (SST), CAPE and some features of the hurricane itself in determining hurricane potential intensity are investigated. The results indicate that existence of CAPE may lead to the steady state (or potential intensity) appreciably different from the otherwise surface entropy flux conversion and surface dissipation balanced state, although CAPE contribution to kinetic energy generation is usually much smaller than that of the surface flux. It is interesting that hurricane potential intensity seems less dependent on the underlying SST than was shown with previous theoretical models. The results also suggest that hurricane size may affect its potential intensity in that larger-sized hurricanes tend to have higher potential intensities. Copyright © 2004 Royal Meteorological Society [source] Efficient Charge Injection from the S2 Photoexcited State of Special-Pair Mimic Porphyrin Assemblies Anchored on a Titanium-Modified ITO AnodeCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2006Mitsuhiko Morisue Dr. Abstract A novel surface fabrication methodology has been accomplished, aimed at efficient anodic photocurrent generation by a photoexcited porphyrin on an ITO (indium,tin oxide) electrode. The ITO electrode was submitted to a surface sol,gel process with titanium n -butoxide in order to deposit a titanium monolayer. Subsequently, porphyrins were assembled as monolayers on the titanium-treated ITO surface via phosphonate, isophthalate, and thiolate groups. Slipped-cofacial porphyrin dimers, the so-called artificial special pair at the photoreaction center, were organized through imidazolyl-to-zinc complementary coordination of imidazolylporphyrinatozinc(II) units, which were covalently immobilized by ring-closing olefin metathesis of allyl side chains. The modified surfaces were analyzed by means of X-ray photoelectron spectroscopy. Photoirradiation of the porphyrin dimer generated a large anodic photocurrent in aqueous electrolyte solution containing hydroquinone as an electron sacrificer, due to the small reorganization energy of the dimer. The use of different linker groups led to significant differences in the efficiencies of anodic photocurrent generation. The apparent flat-band potentials evaluated from the photocurrent properties at various pH values and under biased conditions imply that the band structure of the ITO electrode is modified by the anchoring species. The quantum yield for the anodic photocurrent generation by photoexcitation at the Soret band is increased to 15,%, a surprisingly high value without a redox cascade structure on the ITO electrode surface, while excitation at the Q band is not so significant. Extensive exploration of the photocurrent properties has revealed that hot injection of the photoexcited electron from the S2 level into the conduction band of the ITO electrode takes place before internal conversion to the S1* state, through the strong electronic communication of the phosphonyl anchor with the sol,gel-modified ITO surface. [source] Electronic Energy Levels in all- trans Long Linear Polyenes: The Case of the 3,20-Di(tert -butyl)-2,2,21,21-tetramethyl-all- trans -3,5,7,9,11,13,15,17,19-docosanonaen (ttbp9) Conforming to Kasha's RuleCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2005Javier Catalán Prof. Dr. Abstract The absorption, fluorescence and fluorescence excitation spectra for 3,20-di(tert -butyl)-2,2,21,21-tetramethyl-all- trans -3,5,7,9,11,13,15,17,19-docosanonaen (ttbP9) in dilute solutions of 2-methylbutane were recorded at temperatures over the range 120,280 K. The high photostability of this nonaene allows us to assert that it exhibits a single fluorescence and that this can be unequivocally assigned to emission from its 11Bu excited state, it being the first excited electronic state. Available photophysical data for this polyene and the wealth of information reported for shorter all- trans polyenes allow us to conclude that if the first excited electronic state for the chromophore possessed 21Ag symmetry, then the energy of such a state might have been so close to that of the 11Bu state that: 1) the radiationless internal conversion mechanism would preclude the observation of the emission from the 11Bu state reported in this work and 2) the 21Ag state reached through internal conversion would be vibrationally coupled to 11Bu and would facilitate the detection of the emission from 21Ag, which was not observed in any of the solvents used in this work. The spectroscopic and photochemical implications of these findings for other polyenes are discussed. [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] Substituent effects on the photofading of disperse azo dyes on poly(ethylene terephthalate) substrateCOLORATION TECHNOLOGY, Issue 3 2010Yasuyo Okada The relationships between the chemical structures and oxidative fading of the disperse azo dyes, p -nitrophenylazo- and benzothiazoleazo-anilines, on poly(ethylene terephthalate) substrate are discussed in terms of the parameters k0,i (rate constants of reaction towards 1O2) and fi (photosensitivity), the molecular parameters of molecular orbital theory and substituents in the diazo and coupling components, on the assumption that the initial rates of oxidative fading are proportional to the product of k0,i and fi. 2-Methoxy-5-acetylamino- N -substituted aniline couplers exhibited large fi values. 2-Chloro and 4-nitro substituents of aniline diazo components exhibited small fi values or high quantum yields of internal conversion, while 4-nitro substituent did not. A close correlation between N -substituents and light fastness, proposed by Müller and supplemented by Dawson, demonstrates the applicability of frontier orbital theory, through the highest occupied molecular orbital (HOMO) energy of the dyes, to the analysis of oxidative fading. Dyes with N -2-cyanoethyl substituents, which gave a lower HOMO energy, also exhibited superior light fastness compared with N -2-hydroxyethyl substituents. [source] | ||||||||||