Effects of Reactants’ Solvation Shell Compositions on Pyrene Fluorescence Quenching by Iodide Anion
Restricted (Penn State Only)
- Author:
- Chettle, Brian
- Area of Honors:
- Chemistry
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Bratoljub Milosavljevic, Thesis Supervisor
Andrew Zydney, Thesis Honors Advisor - Keywords:
- Physical Chemistry
solvation
photophysics
photochemistry
laser photolysis
spectroscopy
fluorescence
pyrene
iodide
heavy atom effect - Abstract:
- In this project, the effects of reactants’ solvation shell composition in pyrene fluorescence quenching by iodide in water-ethanol mixtures have been examined using a nanosecond pulse laser photolysis technique. Pyrene was chosen as the reactant due to its photophysical properties; namely, the III/I ratio in its fluorescence spectrum was previously found to be sensitive to the medium polarity. Since the medium polarity depends on medium composition, it is possible to determine the medium composition from the medium polarity measurements. In this work, the III/I ratio was measured as a function of solvent composition and used to assess the pyrene solvation shell composition. Counterintuitively, preferential solvation with ethanol was observed. The rate constant of pyrene fluorescence spontaneous decay was also measured as a function of solvent molar composition; even more pronounced preferential solvation by ethanol was observed. The fluorescence quencher, iodide anion, exhibits charge-transfer-to-solvent (CTTS) absorption band, which is also sensitive to solvent polarity. The CTTS spectral peak position was measured as a function of molar fraction, and it was used to assess the iodide ion solvation shell composition. The laser photolysis transient absorption spectroscopy experiment showed that the pyrene triplet state concentration increases with the degree of quenching, which indicates that the quenching mechanism is a heavy atom effect. The quenching rate constant dependence on solvent molar composition deviates from ideal behavior, which can be predominately attributed to the non-ideal dependence of viscosity on the solvent molar composition. However, the deviation from the Stokes-Einstein equation, primarily at high mole fractions of ethanol, may be attributed to reactant solvation effects.