Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Gerald J. Small

Second Advisor

Walter S. Struve

Abstract

Pump probe and hole burning spectroscopies have been used to study the electronic excitation transport (EET) in photosynthetic antenna and the initial charge separation in reaction center proteins. A theoretical description of time dependent polarized fluorescent and optical density transients arising from EET transport for solutions of randomly oriented chromoproteins is developed and extended to oriented monolayers of chromoproteins. The initial parallel to perpendicular ratio is found to be 3:1 regardless of the system dimensionality or chromoprotein organization. Residual anisotropy at long times is found to be directly related to the relative orientation of the donor and acceptor chromophores;Pump probe experiments performed on the Q[subscript] y band of the Bchl a-protein antenna complex from Prosthecochloris aestuarii shows that excitation transport occurs largely through incoherent hopping between localized states at times greater than 2 ps. The fact that early time ratios significantly less than 3:1 are found is taken as evidence for ultrafast exciton localization between exciton components occurring much faster than 2 ps;Temperature dependent polarized photobleaching dynamics is investigated through 680 nm pump probe experiments in the chl a antenna of native photosystem I particles from spinach. The results show that the anisotropic decay is lengthened by an order of magnitude when the temperature is lowered from 290 K to 38 K. Most of the increase occurs below 65 K which indicates that protein phonons play a significant role in EET. The isotropic decay is much less temperature sensitive and indicates that the anisotropic and isotropic decays are from different energy transport processes. A multiphonon excitation theory is detailed and used to show that phonon assisted EET occurs from localized independent modes about the donor and acceptor;Photochemical hole burning spectroscopy was used to study the protonated and deuterated reaction centers from the purple bacterium Rhodobacter sphaeroides. The data establish that the lifetime of P870[superscript]* is invariant to the burn frequency within the inhomogeneous distribution of zero phonon lines and to temperature between 1.6 and 8.0 K. The high signal to noise obtained for the data allow for stringent testing of a previously used theoretical model to simulate hole profiles and absorption spectra. Although the essential physics is not altered, the modeling of the distribution of low frequency phonons which couples to P870[superscript]* was found to be inadequate.

DOI

https://doi.org/10.31274/rtd-180813-11522

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Paul A. Lyle

Language

en

Proquest ID

AAI9321191

File Format

application/pdf

File Size

258 pages

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