A detailed study of the excited state energy migration dynamics that take place within an assembly of Ru(II) and Os(II) polypyridyl complexes linked together through a polymer backbone is presented. The energy migration process is initiated by the photoexcitation of the metal-to-ligand charge transfer (MLCT) transition in one of the Ru(II) complexes and terminated by energy transfer to a lower energy Os(II) trap. Energy transfer sensitization of Os(II) can occur in a single step if the excited state is formed adjacent to a trap, or after a series of hops between isoenergetic rutheniums prior to reaching a trap. The dynamics of the energy transfer process are followed by monitoring the growth of Os(II) luminescence at 780 nm. The kinetics of the growth are complex and can be fit by a sum of two exponentials. This kinetic complexity arises both from the presence of a distribution of donor-acceptor distances and the variety of time scales by which Os(II) can be formed. We have augmented the time-resolved experiments with Monte Carlo simulations, which provide insight into the polymer array's structure and at the same time form the basis of a molecular-level description of the energy migration dynamics. The simulations indicate that the most probable Ru-->Os energy transfer time is approximately 400 ps while the time scale for Ru-->Ru hopping is approximately 1-4 ns. The time scale for Ru-->Ru hopping relative to its natural lifetime (1000 ns) suggests that this polymer system could be extended to considerably longer dimensions without an appreciable loss in its overall efficiency.
A molecular assembly based on derivatized polystyrene is described, which mimics both the light-harvesting and energy-conversion steps of photosynthesis. The system is unique in that the two key parts of a photosynthetic system are incorporated in a functional assembly constructed from polypyridine complexes of Ru II . This system is truly artificial, as none of the components used in construction of the assembly are present in a natural photosynthetic system. Quantitative evaluation of the energy and electron transfer dynamics after transient irradiation by visible light offers important insights into the mechanisms of energy transport and electron transfer that lead to photosynthetic light-to-chemical energy conversion. In natural photosynthesis, light is converted into chemical energy by a sequence of coupled energy and electron transfer events. Initially, sunlight is absorbed by light-harvesting pigments, chlorophylls and carotenoids, which act as antenna fragments. The energy collected by absorption creates molecular excited states and is subsequently transferred between chromophores through an energy cascade ultimately reaching the reaction center. At the reaction center, the light energy is converted into chemical energy by a series of electron transfer steps (1-5). Understanding of these concepts has motivated chemists to design assemblies that have related properties and may provide the basis for artificial solar energy conversion devices (6 -10). The construction of a functional and efficient artificial solar energy conversion device would have a significant impact on our ability to use solar energy.To date, most research on the artificial solar energy conversion has focused on mimicking various aspects of natural photosynthesis. Through these studies, a reasonable understanding of various components necessary for construction of an artificial photosynthetic system has been developed. The main challenge at the moment is to assemble these components in a spatially organized manner, which will allow their efficient collaboration in harvesting the light energy and converting it efficiently into chemical energy. There are currently two strategies. One is based on constructing complex supramolecular assemblies in which the various components are linked together by chemical bonds (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). The second utilizes various supports such as polymers (23-32), zeolites (33-38), sol-gel glasses (39 -41), lipid membranes (42, 43), or selfassembled films (44 -47) as scaffolds for incorporating and organizing the necessary components.Derivatized polymers provide an attractive approach to this problem because they offer f lexibility and simplicity in the design of multifunctional assemblies. We (23-28) and others (29 -32) have used derivatized polymers to gain insight into various aspects of the photosynthetic process. Recently, we showed, for example, that polymeric assemblies derivatized with polypyridyl complexes of Ru II and Os II display antenna and energy transport properties ...
The acid-functionalized tris-heteroleptic chromophore--donor--acceptor assembly [RuII(bpyCOOH)(bpyCH2PTZ)(bpyCH2MV2+)](PF6)4]4+ (1) (bpyCOOH = 4'-methyl-2,2'-bipyridine-4-carboxylic acid; bpyCH2PTZ = 10-((4'-methyl-2,2'-bipyridin-4-yl)methyl)phenothiazine; bpyCH2MV2+ = 1-((4'-methyl-2,2'-bipyridin-4-yl)methyl)-1'-methyl- 4,4'-bipyridinediium) was synthesized in a one-pot reaction by careful selection of the order of ligand addition to RuCl2(DMSO)4 (DMSO = dimethyl sulfoxide). The success of this method was based upon separation and isolation of 1 from mixtures containing ligand-scrambled products by cation exchange chromatography. Metal-to-ligand charge-transfer (MLCT) excitation in acetonitrile at 464 nm was followed by intramolecular electron transfer to give a redox-separated state [RuII(bpyCOOH)(bpyCH2PTZ.+)(bpyCH2MV.+)]4+ with an efficiency of eta RS = 0.35 +/- 0.05.
This article examines how the Simpson case affected newspaper coverage of domestic violence. We analyzed the frequency with which domestic violence was covered and the content of that coverage in the New York Times, the Inquirer and Philadelphia Daily News. As expected, the number of non-Simpson domestic violence stories increased immediately after the event but declined in the majority of newspapers afterwards. The hypothesis that domestic violence story coverage would shift from incident focused to socially focused reporting was not generally supported. Social coverage was present across all domestic violence stories before the Simpson event, and with only minor variations, the overall coverage content did not change.
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