Lin, C. T. (Chhui-Tsu)
M.S. (Master of Science)
Department of Chemistry
Solution (Chemistry); Porous materials; Photochemistry
The purpose of this thesis is to investigate the photophysical and photochemical properties of embedded solutes in porous Vycor glass. The emission and excitation spectra of quinoline and 2,3-dichloroquinoxaline embedded in a calcined (600°C) porous Vycor glass and dissolved in different solvents were recorded at various temperatures. The spectral characteristics and phosphorescence lifetimes of adsorbates were observed to be identical with those in a 0.5 N sulfuric acid solution, indicating proton transfer from the surface to the N-heterocyclics. The strong surface-adsorbate interaction is further revealed by the dynamic study of adsorbates at 77K and 4.2K. Emission spectra and lifetimes at 77K are reported for samples prepared by adsorbing benzo(c)cinnoline (9,10-diazaphenanthrene; 9,10-dp) in calcined Vycor glass. For Vycor glass calcined at 300, 400, 600, and 900°C, the embedded species are identified as hydrogen-bonded 9,10-dp, protonated 9,10-dp, protonated dihydro-9,10-dp, and protonated carbazole, respectively. The transformations are explained as resulting from an increase in the surface Brønsted acidity of Vycor glass upon calcination. The observed transformation is shown to be surface-induced in nature and occurs readily inside the porous Vycor glass. The low-temperature (77K) emission technique has also been used to examine the photophysical properties of embedded benzophenone (BP), acetophenone (AP), and p-methoxyacetophenon (MAP) in the calcined Vycor glass. For all calcining temperatures, the Vycor glass only provided different polar environments for BP and AP. However, at the calcining temperatures of 600°C and 900°C, the surface-induced transformation of MAP was observed. By comparing the emission properties of embedded MAP with acidic MAP solutions having various pH values, the acidity of the calcined (600°C) Vycor glass was calibrated to be between pH=2.6 and 3.6. The importance of the T₁, ³ᴨ,ᴨ*, state of the embedded solute for the surface-induced reaction is also discussed.
Hsu, Wenlie, "Spectroscopic studies of solutes embedded in porous Vycor glass" (1988). Graduate Research Theses & Dissertations. 5013.
ix, 123 pages
Northern Illinois University
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