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2,5-Dimethyl-2,4-hexadiene induced photodechlorination of 9,10-dichloroanthracene
Saltiel, J.,Smothers, W.K.,Schanze, K.S.,Charman, S.A.,Bonneaub, R. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.6
Photochemical formation of 9-chloroanthracene (MCA) from 9,10-dichloroanthracene (DCA) is observed in the presence of 2,5-dimethyl-2,4-hexadiene (DMH) in acetonitrile (AN). The mechanism of the reaction was investigated using kinetics, deuterium labeling, and quenching techniques. Contrary to conclusions in a recent publication, our work supports the salient features of the mechanism we had proposed earlier. DCA is photostable in degassed AN in the absence of DMH. When DMH is added, irradiation of DCA at 365 or 404 nm converts it quantitatively to MCA. The photoreaction is strongly inhibited when low concentrations of molecular oxygen or 1,2,4,5-tetracyanobenzene are also present. Results from fluorescence quenching studies along with kinetics parameters from the dependence of DCA loss and MCA formation quantum yields on [DMH] implicate participation of the DCA/DMH singlet exciplex, the DCA/$(DMH)_2$ triplex and the DCA radical anion ($DCA^{{\cdot}-}$) as intermediates in the photodechlorination. Results from experiments using deuterated DMH, deuterated AN, and AN containing $D_2O$ or $H_2O$ show that the 10-H of MCA is introduced by protonation of $DCA^{{\cdot}-}$. Contrary to a recent report, there is no radical pathway to MCA via dissociation of $DCA^{{\cdot}-}$ to chloride and $MCA^{\cdot}$ radical. Changes in the absorption spectrum of DCA in AN with increasing [DMH] suggest that the static quenching of DCA fluorescence at high [DMH] is due primarily to nearest neighbour quenching instead of DCA/DMH ground state complex formation.
Polymer-based chromophore–catalyst assemblies for solar energy conversion
Leem Gyu,Sherman Benjamin D.,Schanze Kirk S. 나노기술연구협의회 2017 Nano Convergence Vol.4 No.37
The synthesis of polymer-based assemblies for light harvesting has been motivated by the multi-chromophore antennas that play a role in natural photosynthesis for the potential use in solar conversion technologies. This review describes a general strategy for using polymer-based chromophore–catalyst assemblies for solar-driven water oxidation at a photoanode in a dye-sensitized photoelectrochemical cell (DSPEC). This report begins with a summary of the synthetic methods and fundamental photophysical studies of light harvesting polychormophores in solution which show these materials can transport excited state energy to an acceptor where charge-separation can occur. In addition, studies describing light harvesting polychromophores containing an anchoring moiety (ionic carboxylate) for covalent bounding to wide band gap mesoporous semiconductor surfaces are summarized to understand the photophysical mechanisms of directional energy flow at the interface. Finally, the performance of polychromophore/catalyst assembly-based photoanodes capable of light-driven water splitting to oxygen and hydrogen in a DSPEC are summarized.
Light and dark biocidal activity of cationic poly(arylene ethynylene) conjugated polyelectrolytes
Corbitt, Thomas S.,Ding, Liping,Ji, Eunkyung,Ista, Linnea K.,Ogawa, Katsu,Lopez, Gabriel P.,Schanze, Kirk S.,Whitten, David G. Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.7
In this paper we report a study of cationic poly(arylene ethynylene) conjugated polyelectrolytes. The objective of the study was to compare the behavior of a polymer where a thiophene has replaced a phenyl ring in poly(phenylene ethynylene) polycations (PPE) previously investigated. Properties of solution phase and physisorbed suspensions of the polymer on microspheres were investigated. The photophysical properties of the polymer are evaluated and used to understand the striking differences in biocidal activity compared to the PPE polymers previously examined. The principal findings are that the thiophene polymer has remarkable dark biocidal activity against Pseudomonas aeruginosa strain PAO1 but very little light-activated activity. The low light-activated biocidal activity of the thiophene polymer is attributed to a highly aggregated state of the polymer in aqueous solutions and on microspheres as a physisorbed coating. This results in low triplet yields and a very poor sensitization of singlet oxygen and other reactive oxygen intermediates. The highly effective dark biocidal activity of the thiophene-containing polymers is attributed to its high lipophilicity and the presence of accessible quaternary ammonium groups. The difference in behavior among the polymers compared provides insights into the mechanism of the dark process and indicates that aggregation of polymer can reduce light activated biocidal activity by suppressing singlet oxygen generation.
Influence of the mixing regime on algal photosynthetic performance in laboratory scale enclosrues
Jacco Kromkamp,Ferdinand Schanz,Machteld Rijkeboer,Elisa Berdalet,Bumchul Kim,Herman J. Gons 江原大學校 附設 環境硏究所 1992 環境硏究 Vol.9 No.-
The photosynthesis of plankton sampled from the eutrophic Lake Loosdrecht was studied in Laboratory Scale Enclosures (LSEs) with regard to the rate of mixing. First, two LSEs were operated at different mixing rates. No significant differences in photosynthetic performance were found, with the exception of a depressed photosynthesis in the afternoon in the LSE which had a low mixing rate. Secondly, when mixing was stopped, the phytoplankton which stayed in the dark due to the steep light gradient in the LSE responded by changing its maximal photosynthetic capacity, The results show that the filamentous cyanobacteria in the lake can respond rapidly to changes in the depth of the mixed layer by altering their photosynthetic performance.