Photochemistry of Triptycene-1,4-Quinone and the control of reaction multiplicity in the solid state
Creators: name: Gamlin, Janet Nathalir
Publisher: name: University of British Columbia
Year: 2009

description: [Chemical Compound Diagram] Three triptycene-l,4-quinoiie derivatives were synthesized and their photochemical rearrangements investigated in solution and in the solid state. The substituents at the 9,10-bridgehead positions affected the outcome of the photochemical reactions in some novel and unexpected ways. Upon direct irradiation of triptycene 63 in acetonitrile in the absence of oxygen, formation of the corresponding dibenzosemibullvalene derivative arising from the di-71-methane rearrangement was observed. Photolysis of the methyl substituted compound 69 led to the formation of the corresponding dibenzosemibullvalene compound as well as a dark blue norcaradiene derivative resulting from a carbene intermediate. Triptycene 72 also rearranged to a small extent to a norcaradiene derivative, but primarily underwent a y-hydrogen abstraction reaction giving a colorless dihydroiuran derivative. Additionally, a dark orange benz[a]aceanthrylene derivative was isolated. Photolysis of triptycene 63 in the presence of oxygen gave a unique triketone derivative. Irradiation of triptycene 63 in chlorinated solvents resulted in chlorinated triptycene quinones. All three starting triptycene- 1,4-quinones were found to be photo chemically inert in the crystalline state. The photoproduct structures were supported by X-ray crystallographic analysis, and possible mechanisms for their formation are presented and discussed. The ability to enhance triplet photochemical behavior of a probe molecule in the solid state was tested by introducing either heavy atoms, which enhance intersystem crossing, or sensitizers, which promote triplet-triplet energy transfer. The efficiency of intersystem crossing as well as triplet-triplet energy transfer was studied by forming salts between photochemically reactive carboxylic acids and either alkali metal hydroxides or organic amines containing an acetophenone moiety. Promising triplet-triplet energy transfer results were established by irradiating salts formed between a P,y-unsaturated keto-acid and several different sensitizer amines. The singlet/triplet photoreactivity of a series of monosubstituted dibenzobarrelene carboxylates (probe molecules) was also analyzed in the crystalline state and in solution. The Li+ , Na+ , K+ , Rb+ and Cs+ salts of the carboxylates as well as salts with various ammonium ion sensitizer components were prepared in order to control the reaction multiplicity in the solid state by the heavy atom effect or by triplet-triplet energy transfer. By monitoring the ratio of singlet photoproduct (dibenzocyclooctatetraene) to triplet photoproduct (dibenzosemibullvalene), the effects of heavy atoms linked to a probe molecule were studied. A general explanation for the increase in triplet product formation in the solid state upon the introduction of heavy atoms was suggested. Solid state triplet-triplet energy transfer was also successfully demonstrated in the salts containing the amine sensitizers. The X-ray crystal structures of the salts were studied in order to establish a correlation between the geometric arrangement of the donor and acceptor and the increase in triplet state reactivity. The observed difference in efficiency of the sensitizers was proposed to result from different excited states.