University of Illinois Urbana-Champaign

Zeolites and Polymer Thin Films as Media for Structuring Light-Induced Electron Transfer Reactions (Rhodamine B, Forster, Energy Migration)

Wilkins, Keith D.

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Description

Title
Zeolites and Polymer Thin Films as Media for Structuring Light-Induced Electron Transfer Reactions (Rhodamine B, Forster, Energy Migration)
Author(s)
Wilkins, Keith D.
Issue Date
1984
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
Abstract
  • Zeolites are characterized as structural templates for light-induced electron transfer reactions. The main emphasis is on factors affecting loading of Ruthenium tris(bipyridine) (Ru(bpy)(,3)('+2)) into the lattice and explaining luminescent decay data in terms of the molecular environment.
  • The loading was found to depend on the {Ru(bpy)(,3)('+2)} in the exchange solution, the length of the exchange and the pH. The zeolite broke down in acidic solution and in the presence of phosphate. In unbuffered solution the Ru(bpy)(,3)('+2) decomposed to a green product.
  • Quenching experiments with tetramethylphenylenediamine (TMPD) show evidence of two emitting species of Ru(bpy)(,3)('+2). Evaluation by curve fitting resolved the decay into two lifetimes. The long lifetime of 897 ns arises from Ru(bpy)(,3)('+2) bound on or near the surface. The short lifetime of about 74 ns is either from Ru(bpy)(,3)('+2) in the interior or from emitting dimers. The possibilities of creating an antenna in the zeolites is also discussed.
  • Fluorescence decay kinetics of rhodamine B (RhB) were examined at concentrations from 5 to 40 mM in polymer films of poly(vinyl acetate) (PVA) and poly(styrene sulfonate, sodium salt) (PSS). The decay kinetics were modified by doping the films with the quencher acid black 24. The polarity of the matrix has a strong effect on exciton migration. In more polar media the fluorescence peak shifts to the red and decreases overlap between the emission and absorption spectra of RhB. Values for R(,o) (RhB-RhB) ranged from 23 (ANGSTROM) in PSS to 54 (ANGSTROM) in PVA. Diffusion coefficients of excitons, D, were evaluated by two and three parameter fits of decays to curves predicted by the theory Yokota and Tamimoto based on a Pade approximant. Values of D increased rapidly to > 10('-3) cm('2)/sec in two parameter fits (zero time intensity, I(,o) and D), but peaked then tailed off when the effective quencher concentration was also allowed to vary. Self-quenching from dimer pairs is the cause of the roll off which begins at {RhB} of 20 mM. At higher concentrations the system behaved according to Forster kinetics with D approaching zero. The ramifications for the construction of energy-gathering antennas is discussed.
Graduation Semester
1984
Type of Resource
text
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