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Synthesis, spectroscopy, solution structural characterization, and electron transfer kinetics of systems designed to probe donor-acceptor electronic coupling modulated by stacked aromatic residues separated by less than the sums of their van der Waals rad

Posted on:2001-10-22Degree:Ph.DType:Thesis
University:University of PennsylvaniaCandidate:Iovine, Peter MFull Text:PDF
This thesis focuses on the synthesis, spectroscopy, dynamical properties, and electron transfer kinetics of novel porphyrin-quinone systems designed to probe donor-acceptor electronic coupling modulated by stacked aromatic residues in which the nature of the aromatic interactions that define the electron transfer medium differ markedly from that thus far delineated in duplex DNA.; Key synthetic achievements of this work include the first synthesis of rigid, π-stacked porphyrin-quinone systems in which the interplanar separation of the Donor, Spacer, and Acceptor lie in the sub van der Waals regime (∼3.0 Å), the application of metal-mediated cross-coupling to novel aromatic architectures, the co-development of a valuable new porphyrinic synthon, and the utilization of various aryl 1,4-diboronic esters. The synthetic route exploits a modular approach in which interchangeable aromatic building blocks are used in the construction of the π manifold thereby allowing facile electronic and steric modification to any aspect of the molecular assembly without significant alteration of the overall synthetic method.; The unique structural features of these π-stacked porphyrin-spacer-quinone systems give rise to disparate shielding effects which distribute uniformly the aromatic 1H resonances for these diamagnetic compounds over extraordinarily large spectral windows that exceed 9.0 ppm. The 2D NMR (NOESY) signatures evince numerous NOE contacts with little to no spectral overlap. An accurate determination of the solution structure for 5-[8-(4-[8-(2,5-Benzoquinonyl)-1-naphthyl]-1-phenyl)-1-naphthyl]-10,20-diphenylporphyrin was accomplished, incorporating NOESY derived proton-proton distances as restraining functions in hybrid molecular dynamics/simulated annealing and molecular mechanics calculations.; The electron transfer dynamics and electrooptic properties of these novel π-stacked donor-acceptor systems were investigated using ultrafast Transient Absorption Spectroscopy. The rate of photoinduced electron transfer and thermal charge recombination events in these species were determined and preliminary estimates as to the distance dependence of electron transfer are presented. Driving force data for the charge separation and charge recombination events were obtained by cyclic voltammetric measurements.
Keywords/Search Tags:Electron transfer, Systems, Spectroscopy, Synthesis, Aromatic, Donor-acceptor
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