Characterization of Structure and Interfacial Energy Transfer of Molecular Thin Films
Fischer, Shirley Gale
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https://hdl.handle.net/2142/67259
Description
Title
Characterization of Structure and Interfacial Energy Transfer of Molecular Thin Films
Author(s)
Fischer, Shirley Gale
Issue Date
1981
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Language
eng
Abstract
Asymmetric environments can be provided at interfaces of thin films, where effective carrier separation and light-driven electron transfer reactions can occur. These reactions are of interest in solar energy and photosynthesis studies.
A spin-coating device is used to fabricate thin films on the order of 2000-5000 (ANGSTROM) thick. These films are manufactured from casting solutions containing solvent, polymer, and a chromophore, usually fluoranthene. Onto this film, submonolayer amounts of perylene are deposited by a vacuum vapor deposition process.
A fluorescence emission spectrum of this film assembly yields a predominant perylene feature, which is distinctly different from that of fluoranthene. This is surprising, since PE receives less than one percent of the excitation light and is outnumbered by FA by a factor of 180 on a number per unit area basis. Approximately 4% of the fluoranthene fluorescence intensity is quenched. This degree of quenching implies an energy transfer distance on the order of 100 (ANGSTROM).
In order to understand these phenomena, the system needed to be better characterized, to determine if experimental artifacts were contributing to this large energy transfer distance. Possible candidates such as inhomogeneity of the fluoranthene film, fluoranthene diffusion and perylene diffusion into the bulk were investigated.
Resolution of these problems involved several spectroscopic techniques such as fluorescence, absorption, Auger electron spectroscopy, and electron spin resonance. The results of these experiments imply no bulk diffusion of perylene or fluoranthene and they show no evidence for surface excess factors. Mechanistic studies indicate the absence of energy migration in the fluoranthene phase. The fluoranthene-perylene energy transfer appears to obey pure Forster kinetics. The critical energy transfer radius was determined to be on the order of tens of Angstroms by two independent methods.
One such method involved experimental data obtained from fluorescence decay curves of a mixed fluoranthene/perylene distribution in the polymer. An extension of theory used to describe this non-radiative quencher mode is derived.
Energy traps are accessible with this system allowing exploitation for solar energy technology. The mechanism of energy transfer here mimics that of photosynthesis, and may serve as a model for that process. In addition, this device is versatile and inexpensive.
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