Photoinduced intramolecular transformations of organic molecules

Yuelie Lu, Purdue University

Abstract

The major part of this dissertation is a study of the photophysical and photochemical properties of aliphatic thioketones in solution and the gas phase. The solution and gas phase photochemical transformations of aliphatic thioketones observed in this work demonstrate that the excited thiocarbonyl function has distinctive characteristics as compared with a carbonyl functionality. The S$\sb2$ state of aliphatic thioketones studied in the gas phase are relatively strongly emissive as compared with those in solution, the S$\sb1$ state is non-emissive, and the T$\rm\sb n$ states are weakly emissive relative to solution. Vibrational excitation of the S$\sb2$ state in the gas phase leads to Norrish Type II chemistry in addition to the insertion chemistry which predominates in solution. The Norrish Type II reaction is rapidly quenched by either adding inert foreign gases or increasing self pressure. The gas phase photolysis of alicyclic thioketones may provide a synthetically useful method to prepare thermostable cyclic enethiols. The photo-induced methyl migrations of methylindenes in the gas phase were studied using 1-$\sp{13}$C-2-methylindene under "normal flow rate" conditions to compare with earlier work under "low flow rate" conditions. The observations are consistent with the latter process giving rise to appreciable amounts of secondary photoproducts. The photophysical properties of benzylic ketones in non-polar hydrocarbon solution and aqueous solution have been studied. There is efficient energy transfer from the benzene ring to the ketones in $\alpha,\alpha\sp\prime$-tetramethyl-2-indanone, $\alpha,\alpha\sp\prime$-tetramethyl-2-tetralone, and 3-phenyl-2-propanone. This is evident in ketone fluorescence after aryl excitation. There is no detectable aryl fluorescence in these benzylic ketones. The facts that ketone fluorescence in 2-indanone is much less than that seen with its $\alpha$-methyl substituted analogue, and photolysis of 2-indanone and 2-benzosuberone at 254 nm in D$\sb2$O leads to faster exchange of the alpha benzyl hydrogens suggest the photoinduced enolization of 2-indanone and 2-benzosuberone would seem to be an important radiationless decay path for the molecules.

Degree

Ph.D.

Advisors

Morrison, Purdue University.

Subject Area

Organic chemistry|Analytical chemistry|Chemistry

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