Previous work from our laboratory has been concerned with investigating the photochemical reactivity of tetrahydro-1,4-naphthalenedione and tetrahydronaphthoquinol systems, both in the solid state and in solution. The fascinating results obtained prompted us to extend the studies to the analogous tetrahydro-1,4-anthracenediones, tetrahydro-5,12-naphthacenediones and tetrahydroanthraquinol systems. Tetrahydro-1,4-anthracenedione is expected to undergo bis-enolization with extreme ease, and therefore its preparation requires mild and neutral conditions. These compounds were prepared by Diels-Alder reaction between o-quinodimethane and p-benzoquinone and other p-substituted quinones o-Quinodimethane was generated in situ by sulphur dioxide extrusion from 3,6-dihydrobenzo[b]oxathiin-2-oxide. The photochemistry of the tetrahydro-1,4-anthracenediones, tetra-hydro-5,12-naphthalenedione and tetrahydroanthraquinols has been investigated both in the solid state and solution. The effect of the solid state medium on the photoreactivity, compared to the solution, is significant; the nature and/or the number of the photoproducts formed in the solid state is generally different from the results obtained in solution. These differences have been explained on the basis of the crystal and molecular structures of the reactants. Special steric effects, which may impede the photochemical reactions in the solid state have been identified. The values of the geometric parameters (d, r and A) for hydrogen atom abstraction are found to be similar to those observed in earlier studies by Scheffer et al. It has been found that the o-quinodimethane/2,3-dimethyl-l,4-naphthoquinone adduct affords, via β-hydrogen atom abstraction and closure of the resulting 1,3-biradical, a cyclopropanol. The cyclopro-panol itself undergoes photolysis initiated by a novel ring opening process. Irradiation of crystals of the adduct does not result in any cyclopropanol. The reasons for the non-reactivity of the Diels-Alder adduct in the solid state have been suggested to be due to the non-bonded steric interactions between the lattice neighbors as shown by the X-ray crystal structure. The photorearrangement of one substrate, namely 2,3,4a,9a-tetra-methyl-4a,9a,9,10-tetrahydro-1,4-anthracenedione is found to be controlled by the temperature, multiplicity, and phase of the reaction. By carrying out the reaction at or above room temperature or in the presence of a sensitizer or in the crystalline state, the reaction can be forced in one direction. Lowering the photolysis temperature causes the formation of another product. The nature of the photoproduct is independent of the temperature in the crystalline state. The results have been interpreted in terms of a required ring inversion which is needed for the formation of the low temperature photoproduct (see Scheme 44). The ring inversion is not allowed in the solid state. / Science, Faculty of / Chemistry, Department of / Graduate

Femtosecond time-resolved transient absorption (fs-TA), nanosecond time-resolved transient absorption (ns-TA), and nanosecond time-resolved resonance Raman spectroscopy (ns-TR3) methods were used to study the behaviors of the transient intermediates involved in the photophysical and photochemical processes of 3-methylbenzophenone (3-MeBP), 3-(hydroxymethyl)benzophenone (m-BPOH), and 2-(1-hydroxyethyl) 9,10-anthraquinone (2-HEAQ). A particular focus of this work was to study the unusual meta methyl activation reactions of these compounds in water-containing solutions. Density functional theory (DFT) calculations were conducted to help make assignments of the observed experimental transient species and to better understand the reaction mechanisms. First, the photophysical and photochemical reactions of m-BPOH were investigated in selected solvents. In acetonitrile (MeCN) the formation of the triplet state of m-BPOH, (denoted as (m-BPOH)3 ), was detected via an intersystem crossing (ISC). In 2-propanol (IPA), (m-BPOH)3 abstracted a hydrogen atom from the solvent molecule to form an aryl ketyl radical. In an acidic mixed aqueous solution at pH 2, the photoredox reaction appeared to be the predominant reaction. In a more acidic aqueous solution with [H+] =1.0 M, the photoredox reaction faced some competition from the overall photohydration reaction. Second, the photophysical and photochemical reactions of 2-HEAQ in MeCN, IPA, and neutral, acid and basic aqueous solutions were studied. The ISC process of 2-HEAQ took place in MeCN with generation of the triplet excited state species of 2-HEAQ, (2-HEAQ)3. In IPA solvent, (2-HEAQ)3 underwent a hydrogen abstraction with the solvent. A photoredox reaction takes place via an initial protonation process of the AQ group that is followed by deprotonation of the methylene C-H bond in aqueous solutions within a pH range from 2 to 10. Under a stronger acidic aqueous condition with [H+] =1.0 M, the photohydration reaction becomes the major reaction. In strong basic solutions (pH=12) only ISC was observed to take place. The unusual photoredox reaction takes place via protonation of the carbonyl oxygen first followed by deprotonation of the C-H bond in the side chain for both m-BPOH and 2-HEAQ. The protonation of the excited carbonyl oxygen group has been widely studied. On the other hand, the deprotonation of methylene C-H bond is unusual. Therefore, this photoredox reaction for m-BPOH and 2-HEAQ is termed as a meta methyl activation reaction. Third, the photophysical and photochemical reactions of 3-MeBP were explored and compared to those of 4-methylbenzophenone (4-MeBP). This work found that 3-MeBP and 4-MeBP exhibit similar behaviors with m-BPOH and 2-HEAQ in MeCN and IPA. In MeCN, both 3-MeBP and 4-MeBP undergo an efficient ISC process producing triplet excited state species, (3-MeBP)3 and (4-MeBP)3, respectively. In IPA, the (3-MeBP)3 and (4-MeBP)3 intermediates were quenched by the hydrogen abstraction reaction with the solvent. In acidic aqueous solutions (pH  2), the protonated carbonyl oxygen species (3-MeBPH+)3 and (4-(MeBPH+)3 are directly observed by fs-TA spectra. In the case of 4-MeBP, a photohydration is detected and the m-(4-MeBPH2O)3 and o-(4-MeBPH2O)1 species are observed. In contrast, an unusual meta methyl activation reaction is observed for 3-MeBP. In a stronger acid aqueous solution ([H+] =1.0 M) the meta methyl activation reaction becomes the predominant reaction. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy