Date of Award

6-1987

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Chemistry

Language

English

Abstract

The pKa and pKa* of 1-pyrenecarboxylic acid (PCA) in a 50% ethanol/water solvent were experimentally (letermined to be 4.3 and 5.2, respectively. The pK8 of pyrene acrylic acid (PAA) in the same solvent was experimentally determined to be 4.6. An excited state equilibrium was not reached at the buffer concentrations used for the pKa* analysis; therefore, a valid value for the pKa* can not be reported at this time, but taking both the experimental results and the calculated pK8.'s into account, it appears that the pKa* of PAA is in the range 6.6 < pKa* < 7.4. The fluorescence of PCA, PAA, and 1-anthroic acid (1-AA) were studied as a function of solvent. The fluorescence of PCA was solvent independent- small spectral shifts as well as the retention of structure were observed in solvents of varying polarity. The fluorescence of 1-AA and PAA exhibited a solvent dependence. The results of both the pKa analysis and the fluorescence studies indicate that the S0 and the S1 states of PCA have a similar geometry, but that the geometry of the S0 and the S1 states of PAA differ. The change in geometry may be the rotation of the carboxyl group from its nearly perpendicular position with the ring in the S0 state to a more coplanar position with the ring in the S1 state. The effects of hydrogen bonding in hexafluoroisopropanol on the spectral properties of PAA were studied, and the results of the studies indicate that PAA forms a hydrogen-bonded complex with hexafluoroisopropanol in both the ground and the excited states.

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In Copyright - Educational Use Permitted.