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Insights into the Photophysical Reac...

Paulus, Bryan Christopher.

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Insights into the Photophysical Reaction Coordinate of 1st Row Transition Metal Chromophores from Vibrational Coherences.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Insights into the Photophysical Reaction Coordinate of 1st Row Transition Metal Chromophores from Vibrational Coherences./
作者:	Paulus, Bryan Christopher.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	277 p.
附註:	Source: Dissertations Abstracts International, Volume: 81-09, Section: B.
Contained By:	Dissertations Abstracts International81-09B.
標題:	Inorganic chemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27742508
ISBN:	9781658483988

Insights into the Photophysical Reaction Coordinate of 1st Row Transition Metal Chromophores from Vibrational Coherences.
Paulus, Bryan Christopher.

Insights into the Photophysical Reaction Coordinate of 1st Row Transition Metal Chromophores from Vibrational Coherences. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 277 p.

Source: Dissertations Abstracts International, Volume: 81-09, Section: B.

Thesis (Ph.D.)--Michigan State University, 2020.

This item must not be sold to any third party vendors.

Controlling the processes which occur following absorption of photon is beneficial for any conceivable application which seeks to convert light into chemical potential. Transition metal chromophores often undergo ultrafast photoinduced transformations which involve significant nuclear motion. This intricate relationship between electronic and nuclear degrees of freedom suggests significant mixing of their wavefunctions and an interdependence of these molecular properties that can map onto the photophysical dynamics. In systems such as these, the rich dynamical information encoded in vibrational coherences can in principle provide unique insight into the nature of this coupling. Furthermore, this has the potential to provide subtle clues for how one could exert some degree of kinetic control through informed structural, compositional, and environmental modifications. This dissertation describes efforts to use excited state vibrational coherences to glean mechanistic information about ultrafast excited state decay in several first-row transition metal chromophore systems and, further, to exploit that information to reengineer the chromophore to alter the photophysical properties.This dissertation begins by using ultrafast transient absorption measurements to provide an updated kinetic model for a series of chromium(III) tris-betadiketonate compounds. Following prompt 4T2 → 2E ISC to the lowest energy excited state, thermally activated back-intersystem crossing repopulates the 4T2 state which internally converts to the ground state on the ~ 1 ps timescale. Steric bulk in the periphery of the molecule reduces the rate of internal conversion resulting in significantly different spectral evolution. Identical low frequency symmetric breathing modes with dephasing times ranging from ~200-2500 fs were identified in the 2E excited state of each molecule. The more rapid dephasing times are likely due to IVR. Similar methodology was then used to characterize the excited state dynamics in a structurally related series of cobalt(III) tris-betadiketonate compounds. Following ligand field excitation into the 1T1g state, each compound had essentially identical biphasic kinetics with ground state recovery occurring with a ~2 ps time constant from an excited state of (t2g)5(eg*) electron configuration. Low frequency metal-ligand breathing modes similar to those observed in the chromium systems were observed with dephasing times consistently on the order of ~200 fs.Finally, two methods to elongate MLCT lifetimes of iron(II) polypyridyl compounds were demonstrated. In the first, the vibrational modes which drive the ultrafast, sub-200 fs MLCT deactivation to the lower energy metal-centered excited states in a [Fe(cage)]2+ control molecule were identified by their coherent oscillations in a transient absorption experiment. These modes were subsequently hindered by incorporation of electronically benign copper(I) atoms to the N4 coordination environments in the periphery of the ligand scaffold resulting in a > 20-fold increase in the MLCT lifetime. In the final study, it was shown that the excited state properties of iron(II) polypyridyl type systems can be systematically and dramatically tuned by swapping out a single bidentate phenanthroline ligand of a [Fe(phen)3]2+ control molecule with stronger-field cyanide or acyclic dicarbene ligands. This modular approach to tuning the kinetics resulted in a > 25-fold increase in the MLCT lifetime and a fundamentally different decay pathway.

ISBN: 9781658483988Subjects--Topical Terms:

3173556
Inorganic chemistry.
Subjects--Index Terms:

Photon absorption

Insights into the Photophysical Reaction Coordinate of 1st Row Transition Metal Chromophores from Vibrational Coherences.
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500 $a Source: Dissertations Abstracts International, Volume: 81-09, Section: B.
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506 $a This item must not be sold to any third party vendors.
520 $a Controlling the processes which occur following absorption of photon is beneficial for any conceivable application which seeks to convert light into chemical potential. Transition metal chromophores often undergo ultrafast photoinduced transformations which involve significant nuclear motion. This intricate relationship between electronic and nuclear degrees of freedom suggests significant mixing of their wavefunctions and an interdependence of these molecular properties that can map onto the photophysical dynamics. In systems such as these, the rich dynamical information encoded in vibrational coherences can in principle provide unique insight into the nature of this coupling. Furthermore, this has the potential to provide subtle clues for how one could exert some degree of kinetic control through informed structural, compositional, and environmental modifications. This dissertation describes efforts to use excited state vibrational coherences to glean mechanistic information about ultrafast excited state decay in several first-row transition metal chromophore systems and, further, to exploit that information to reengineer the chromophore to alter the photophysical properties.This dissertation begins by using ultrafast transient absorption measurements to provide an updated kinetic model for a series of chromium(III) tris-betadiketonate compounds. Following prompt 4T2 → 2E ISC to the lowest energy excited state, thermally activated back-intersystem crossing repopulates the 4T2 state which internally converts to the ground state on the ~ 1 ps timescale. Steric bulk in the periphery of the molecule reduces the rate of internal conversion resulting in significantly different spectral evolution. Identical low frequency symmetric breathing modes with dephasing times ranging from ~200-2500 fs were identified in the 2E excited state of each molecule. The more rapid dephasing times are likely due to IVR. Similar methodology was then used to characterize the excited state dynamics in a structurally related series of cobalt(III) tris-betadiketonate compounds. Following ligand field excitation into the 1T1g state, each compound had essentially identical biphasic kinetics with ground state recovery occurring with a ~2 ps time constant from an excited state of (t2g)5(eg*) electron configuration. Low frequency metal-ligand breathing modes similar to those observed in the chromium systems were observed with dephasing times consistently on the order of ~200 fs.Finally, two methods to elongate MLCT lifetimes of iron(II) polypyridyl compounds were demonstrated. In the first, the vibrational modes which drive the ultrafast, sub-200 fs MLCT deactivation to the lower energy metal-centered excited states in a [Fe(cage)]2+ control molecule were identified by their coherent oscillations in a transient absorption experiment. These modes were subsequently hindered by incorporation of electronically benign copper(I) atoms to the N4 coordination environments in the periphery of the ligand scaffold resulting in a > 20-fold increase in the MLCT lifetime. In the final study, it was shown that the excited state properties of iron(II) polypyridyl type systems can be systematically and dramatically tuned by swapping out a single bidentate phenanthroline ligand of a [Fe(phen)3]2+ control molecule with stronger-field cyanide or acyclic dicarbene ligands. This modular approach to tuning the kinetics resulted in a > 25-fold increase in the MLCT lifetime and a fundamentally different decay pathway.
590 $a School code: 0128.
650 4 $a Inorganic chemistry. $3 3173556
650 4 $a Physical chemistry. $3 1981412
650 4 $a Chemistry. $3 516420
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653 $a Vibrational coherence
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