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DiScipio_Regina_Dissertation.pdf (14.69 MB)

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Light, Matter, Action: Electronic Relaxation Processes in Biomolecular Photosensitizers and in Photovoltaics

DiScipio, Regina
http://orcid.org/0000-0001-9584-0499
http://rave.ohiolink.edu/etdc/view?acc_num=case1522958286743542

Abstract Details

2018, Doctor of Philosophy, Case Western Reserve University, Chemistry.
Whether interrogating biomolecules for the reactivity as a photosensitizer or metal complexes for their potential for charge separation in a photovoltaic; understanding of the excited state dynamics is critical. Ultrafast broadband transient absorption spectroscopy was used in conjunction with steady-state spectroscopies and time-dependent density functional theory level computations in order to propose excited-state relaxation mechanisms. The characterization and quantification that coincides with the excited-state relaxation mechanism is useful for proposing avenues for in situ reactivity. For the class of biomolecules, pterins, it was shown that UV light populates a vibrationally-hot fluorescent 1pp* state. While the excess vibrational energy is redistributed (ca. 0.2 ps), intersystem crossing (ISC) occurs to an isoenergetic 3np* state from which the population either internally converts to the 3pp* state or undergos electron transfer to generate a neutral radical species. It is proposed that the radical species is responsible for the unimolecular and bimolecular photodegradation that has been observed of the pterins. Similarly, zinc(II)-chelating tetraphenylazadipyrrolmethene and derivatives utilizing different metal centers (cobalt(II) and nickel(II)) and ligands with expanded conjugation and fluorination were explored. The general relaxation mechanism is that visible light populates two nearly degenerate ligand-to-ligand pp* states (2S+1¿). Internal conversion populates the lower energy state which undergoes some energy redistribution, either vibrational cooling or relaxation dynamics, before undergoing ground-state recovery by charge recombination. It was determined that an addition ultrafast ground state recovery pathway exists between when cobalt(II) and nickel(II) are used as the central metal that is inaccessible when zinc(II) is used. The charge recombination lifetime correlates with the power conversion efficiency acquired for these complexes when used as the electron acceptor in combination with the electron donor poly(3-hexylthiophene) (P3HT) in organic photovoltaic devices.
Carlos Crespo-Hernández (Advisor)
Geneviève Sauvé (Committee Chair)
Emily Pentzer (Committee Member)
Mary Barkley (Committee Member)
Nancy Oleinick (Committee Member)
203 p.
Analytical Chemistry; Chemistry; Physical Chemistry
ultrafast, fs, transient absorption spectroscopy, TAS, pterins, pterin, carboxypterin, biopterin, neopterin, formylpterin, PT, organic photovoltaics, OPV

Recommended Citations

Citations

  • DiScipio, R. (2018). Light, Matter, Action: Electronic Relaxation Processes in Biomolecular Photosensitizers and in Photovoltaics [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1522958286743542

    APA Style (7th edition)

  • DiScipio, Regina. Light, Matter, Action: Electronic Relaxation Processes in Biomolecular Photosensitizers and in Photovoltaics. 2018. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1522958286743542.

    MLA Style (8th edition)

  • DiScipio, Regina. "Light, Matter, Action: Electronic Relaxation Processes in Biomolecular Photosensitizers and in Photovoltaics." Doctoral dissertation, Case Western Reserve University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1522958286743542

    Chicago Manual of Style (17th edition)

case1522958286743542
200
© 2018, some rights reserved.Creative Commons License Light, Matter, Action: Electronic Relaxation Processes in Biomolecular Photosensitizers and in Photovoltaics by Regina DiScipio is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.
Release 3.2.12