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Photophysical Processes (photophysical + process)
Selected AbstractsPhotophysical Processes in ,Supramolecular Balls' Formed by Lanthanide Chloride with 2,2,-BipyridineHELVETICA CHIMICA ACTA, Issue 11 2009Abstract The europium complex [EuCl2(bpy)2(H2O)2]Cl,1.25,C2H6O,0.37,H2O, where bpy is 2,2,-bipyridine, was synthesized and investigated with the aim to relate its molecular geometry and crystal packing to the efficiency of energy-transfer processes. The presence of H-bonds between noncoordinated Cl, ions and coordinated H2O molecules leads to the formation of discrete trimers assembled by a number of CH,,,Cl and stacking interactions into ,supramolecular balls' which contain Cl, ions and solvate molecules (H2O and EtOH). The additional stabilization of the complex is due to intramolecular N,,,C interactions between two bpy ligands that causes some shortening of the EuN bonds. Deciphering the luminescence properties of the Eu complex was performed under consideration of both the composition of the inner coordination sphere and the peculiarities of the crystal packing. The influence of the latter and the bpy orientation on the energy of the ligand,Eu charge-transfer state (LMCT) was established, and an additional excited state induced by the , -stacking interaction (SICT) was identified. [source] Primary Photophysical Processes in Photosystem II: Bridging the Gap between Crystal Structure and Optical SpectraCHEMPHYSCHEM, Issue 6 2010Thomas Renger Prof. Dr. Abstract This Minireview summarizes our current knowledge of the optical properties of photosystem II (PS-II) and how these properties are related to the photosynthetic function, that is, excitation energy transfer from the antenna complexes to the reaction center (RC) and the subsequent transmembrane charge separation in the latter. Interpretation of the optical spectra of PS-II is much more difficult than for the RC of purple bacteria, due to the "spectral congestion" problem, namely, the strong spectral overlap of optical bands in PS-II. Recent developments in deciphering the optical properties of the pigments in PS-II, the identification of functional states, and the kinetic details of the primary excitation energy and charge-transfer reactions are summarized. The spectroscopic term P680 that is generally used in the literature no longer indicates the same entity in its cationic and singlet excited form but different subsets of the six innermost pigments of the RC. The accessory chlorophyll ChlD1 forms a sink for singlet excitation and triplet energy and most likely represents the primary electron donor in PS-II. In this respect, a special chlorophyll monomer in PS-II plays the role of the special pair in purple bacteria. Evidence that exciton transfer between the core antenna complexes CP43 and CP47 and the RC is the bottleneck for the overall photochemical trapping of excitation energy in PS-II is discussed. A short summary is provided of PS-II of Acaryochloris marina, which mainly contains chlorophyll d instead of the usual chlorophyll a. This system does not suffer from the spectral congestion problem and, therefore, represents an interesting model system. The final part of this Minireview provides a discussion of challenging problems to be solved in the future. [source] Oligothiophenes Nano-organized on a Cyclotetrasiloxane Scaffold as a Model of a Silica-Bound Monolayer: Evidence for Intramolecular Excimer FormationCHEMISTRY - A EUROPEAN JOURNAL, Issue 46 2009Wojciech Mróz Abstract Excimer formation in a new class of terthiophene-based fluorophores covalently bonded to a cyclotetrasiloxane scaffold has been demonstrated and the photophysical process ruling it has been investigated in detail and modeled theoretically. In contrast to the conventional systems in which long-living fluorophores such as pyrene are linked in the same molecule, an excimer is formed only when two terthiophene-based branches nano-organized on the same cyclotetrasiloxane scaffold are close enough together when excitation takes place. In such a case, excimer formation is extremely efficient, and the new bound excited states are quite stable. [source] Triplet Formation in Fullerene Multi-Adduct Blends for Organic Solar Cells and Its Influence on Device PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Clare Dyer-Smith Abstract In organic solar cells, high open circuit voltages may be obtained by choosing materials with a high offset between the donor highest occupied molecular orbital (HOMO) and acceptor lowest unoccupied molecular orbital (LUMO). However, increasing this energy offset can also lead to photophysical processes that compete with charge separation. In this paper the formation of triplet states is addressed in blends of polyfluorene polymers with a series of PCBM multi-adducts. Specifically, it is demonstrated that the formation of such triplets occurs when the offset energy between donor ionization potential and acceptor electron affinity is ,1.6 eV or greater. Spectroscopic measurements support a mechanism of resonance energy transfer for triplet formation, influenced by the energy levels of the materials, but also demonstrate that the competition between processes at the donor,acceptor interface is strongly influenced by morphology. [source] Astrophysical laser operating in the O i 8446-Å line in the Weigelt blobs of , CarinaeMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005S. Johansson ABSTRACT Within the framework of a simple model of photophysical processes in the Weigelt blobs in the vicinity of the luminous blue variable (LBV) star , Carinae, we explain the presence of the fluorescent ,O i, 8446-Å and forbidden [O i] 6300-Å lines as well as the absence of the allowed O i 7774-Å line in spectra recorded with the Hubble Space Telescope (HST)/STIS instrument (Gull et al.). From atomic data and estimated stellar parameters we demonstrate that there is a population inversion and stimulated emission in the 3p 3P,3s 3S transition ,8446 due to photoexcitation by accidental resonance (PAR) by H Ly, radiation. [source] Dual Chromophore-Nitroxides: Novel Molecular Probes, Photochemical and Photophysical Models and Magnetic MaterialsPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Gertz I. Likhtenstein Over the last decades scientists have faced growing requirements in novel methods of fast and sensitive analysis of antioxidant status of biological systems, spin redox probing and spin trapping, investigation of molecular dynamics, and of convenient models for studies of photophysical and photochemical processes. In approaching this problem, methods based upon the use of dual chromophore-nitroxide (CN) compounds have been suggested and developed. A CN consists of two molecular sub-functionality (a chromophore and a stable nitroxide radical) tethered together by spacers. In the dual compound the nitroxide is a strong intramolecular quencher of the fluorescence from the chromophore fragment. Reduction to hydroxylamine, oxidation of the nitroxide fragment or addition of an active radical yield the fluorescence increase and the parallel decay of the fragment electron spin resonance (ESR) signal. At certain conditions the dual molecules undergo photomagnetic switching and form excited state multi-spin systems. These unique properties of CN were intensively exploited as the basis for several methodologies, which include molecular probing, modeling intramolecular photochemical and photophysical processes, and construction of new magnetic materials. [source] Porphyrin-Appended Europium(III) Bis(phthalocyaninato) Complexes: Synthesis, Characterization, and Photophysical PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2007Yongzhong Bian Dr. Abstract Mixed cyclization of 3-mono-, 4-mono-, or 4,5-di(porphyrinated) phthalonitrile compounds 2, 3, or 6 and unsubstituted phthalonitrile with the half-sandwich complex [EuIII(acac)(Pc)] (Pc=phthalocyaninate, acac=acetylacetonate) as the template in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in n -pentanol afforded novel porphyrin-appended europium(III) bis(phthalocyaninato) complexes 7,9 in 30,40,% yield. These mixed tetrapyrrole triads and tetrad were spectroscopically and electrochemically characterized and their photophysical properties were also investigated with steady-state and transient spectroscopic methods. It has been found that the fluorescence of the porphyrin moiety is quenched effectively by the double-decker unit through an intramolecular photoinduced electron-transfer process, which takes place in several hundred femtoseconds, while the recombination of the charge-separated state occurs in several picoseconds. By using different phthalocyanines containing different numbers of porphyrin substituents at the peripheral or nonperipheral position(s) of the ligand, while the other unsubstituted phthalocyanine remains unchanged in these double-deckers, the effects of the number and the position of the porphyrin substituents on these photophysical processes were also examined. [source] | ||||||||||