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Excited State Dynamics, Molecular In...

Sabatini, Randy Pat.

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Excited State Dynamics, Molecular Interactions, and Electron Transfer in Systems for the Photochemical Production of Hydrogen.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Excited State Dynamics, Molecular Interactions, and Electron Transfer in Systems for the Photochemical Production of Hydrogen./
作者:	Sabatini, Randy Pat.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2015,
面頁冊數:	306 p.
附註:	Source: Dissertation Abstracts International, Volume: 77-01(E), Section: B.
Contained By:	Dissertation Abstracts International77-01B(E).
標題:	Alternative Energy. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3723308
ISBN:	9781339060347

Excited State Dynamics, Molecular Interactions, and Electron Transfer in Systems for the Photochemical Production of Hydrogen.
Sabatini, Randy Pat.

Excited State Dynamics, Molecular Interactions, and Electron Transfer in Systems for the Photochemical Production of Hydrogen. - Ann Arbor : ProQuest Dissertations & Theses, 2015 - 306 p.

Source: Dissertation Abstracts International, Volume: 77-01(E), Section: B.

Thesis (Ph.D.)--University of Rochester, 2015.

This item is not available from ProQuest Dissertations & Theses.

Photochemical H2 production involves the absorption of light by a chromophore, subsequent electron transfer to a catalyst, reduction of protons to form H2, and then regeneration of the chromophore to continue the cycle. While H2 is produced on the order of minutes and hours, the preceding processes occur on a much faster timescale, from seconds to femtoseconds. Electron transfer from chromophore to catalyst competes with a number of other excited state dynamics, all of which can vary wildly from system to system. This thesis will document both the H2 production and spectroscopic characterization of a series of different organic and inorganic chromophores. By measuring such rates as internal conversion, intersystem crossing, and energy and electron transfer, an understanding of the relative activities was attained, as well as intuition on how to improve upon the system.

ISBN: 9781339060347Subjects--Topical Terms:

1035473
Alternative Energy.

Excited State Dynamics, Molecular Interactions, and Electron Transfer in Systems for the Photochemical Production of Hydrogen.
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245 1 0 $a Excited State Dynamics, Molecular Interactions, and Electron Transfer in Systems for the Photochemical Production of Hydrogen.
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300 $a 306 p.
500 $a Source: Dissertation Abstracts International, Volume: 77-01(E), Section: B.
500 $a Advisers: David W. McCamant; Richard Eisenberg.
502 $a Thesis (Ph.D.)--University of Rochester, 2015.
506 $a This item is not available from ProQuest Dissertations & Theses.
520 $a Photochemical H2 production involves the absorption of light by a chromophore, subsequent electron transfer to a catalyst, reduction of protons to form H2, and then regeneration of the chromophore to continue the cycle. While H2 is produced on the order of minutes and hours, the preceding processes occur on a much faster timescale, from seconds to femtoseconds. Electron transfer from chromophore to catalyst competes with a number of other excited state dynamics, all of which can vary wildly from system to system. This thesis will document both the H2 production and spectroscopic characterization of a series of different organic and inorganic chromophores. By measuring such rates as internal conversion, intersystem crossing, and energy and electron transfer, an understanding of the relative activities was attained, as well as intuition on how to improve upon the system.
520 $a Chapter 1 describes the theory involved with this thesis. Chapter 2 details the methods used to characterize the systems studied. Chapter 3 provides an introduction to molecular chromophores currently in the literature.
520 $a Chapter 4 describes a series of Boron-dipyrromethene (Bodipy) dyes, which were studied to determine the effects of the triplet state on photochemical hydrogen production. Halogens (Br, I) were added to the 2,6 positions of the parent dye in order to increase spin-orbit coupling, facilitating intersystem crossing. Ultrafast transient absorption spectroscopy (TAS) revealed the lifetime of the singlet excited state (S1) to be 3-5 ns, 1.2 ns, and 130 ps for the parent, brominated, and iodinated dye, respectively. The decrease in S1 lifetime throughout the series is attributed to an increase in the rate of intersystem crossing. Using platiized titanium dioxide (Pt-TiO2), only the halogenated dyes were active for photochemical hydrogen production, suggesting that the long-lived triplet state is necessary for bimolecular electron transfer, and thus H2 production.
520 $a In Chapter 5, a series of Bodipy dyes are used in conjunction with a cobalt dimethylglyoxime (Co(dmg)) catalyst. Only halogenated Bodipy chromophores were active for H2 production, and dyes with a mesityl substituent were more stable than those with a phenyl substituent, due to the more basic nature of the aryl. Although recent literature articles describe H2 production using a Bodipy -- Co(dmg) dyad, the higher activity from this study, using discrete molecules, sheds doubt that the dyad actually remains intact upon photolysis.
520 $a Chapter 6 compares the activity of chalcogenorhodamine dyes, attached to TiO2, used in dye sensitized solar cells (DSSCs) and photochemical H2 production systems. While the oxygen and selenium derivative performed similarly in DSSCs, the selenium derivative greatly outperformed its oxygen counterpart in H2 production. TAS revealed ultrafast electron transfer in conditions similar to DSSCs but not in conditions similar to H2 production, making the long-lived triplet state only beneficial in H2 production. The discrepancy in electron transfer rates appears to be caused by the presence or absence of aggregation in the system, altering the coupling between the dye and TiO2. This finding demonstrates the importance of understanding the differences between, as well as the effects of the conditions for DSSCs and solar hydrogen production.
520 $a Chapter 7 describes a photophysical comparison of a large group of rhodamine dyes, characterizing the deactivation pathways upon excitation. One major result was that the thienyl dyes have shorter lifetimes than their phenyl counterparts, yet they have similar activity when attached to Pt-TiO 2 for photochemical H2 production. This was attributed to better coupling to the surface of TiO2, due to a smaller dihedral angle between the xanthylium core and aryl. The relevance of both the charge-separated and triplet state was also studied for the different derivatives. In Chapter 8, dyads consisting of a Bodipy chromophore and a Pt(diimine)(dithiolate) complex were studied both spectroscopically and for H2 production. To produce H2 effectively, excitation of either moiety should result in electron transfer from the Pt complex to the catalyst. However, excitation of the Bodipy moiety results in singlet energy transfer to the Pt singlet excited state, rapid intersystem crossing, and then triplet energy transfer back to the Bodipy triplet state. Two methods, lowering the solvent dielectric and placing electron withdrawing groups on the diimine, were found to lower the energy of the Pt triplet state, making triplet energy transfer unfavorable. H2 production of several dyads, attached to Pt-TiO2, all showed light harvesting improvement of the dyad relative to the Pt complex by a factor of 2-4. The insensitivity to the triplet alignment is attributed to the strong coupling of the dyad to the surface of TiO2, which results in a much faster rate of electron transfer than that of triplet energy transfer.
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