Thesis (Ph.D)--Bowling Green State University, 2006. / Document formatted into pages; contains xv, 366 p. : ill. Includes bibliographical references.

Three classes of new photoreactions were discovered and their reaction mechanisms investigated. These reactions are related in that the same critical o-quinonemethide intermediate is involved in the mechanism of each reaction. The first reaction is the photocyclization of 2-(2’-hydroxyphenyl)benzyl alcohol (1) and derivatives to 6H-dibenzo[b,d]pyrans (e.g., 7 from 1), with excellent chemical (>95%) and quantum yields (Φp = 0.50 for 7 from 1 in basic solution). Results from investigations of structure-reactivity, pH-effects and fluorescence data suggest that, in neutral solution, the primary photochemical step involves ionization of the phenol moiety to phenolate ion in S1, which is probably concerted with twisting of the phenyl rings, to give a more planar species in S,. The subsequent dehydroxylation step of the benzyl alcohol moiety, to give o-quinonemethide 20, is initiated by a charge transfer from phenolate to the adjacent phenyl ring. The thermal ring closure of 20 competes with nucleophilic solvent (e.g., H20 or MeOH) capture, to give observed pyran 7 and alcohol 1 (by H20) and 5 (by MeOH), respectively. In moderately strong acidic media, acid-catalyzed photosolvolysis occurs, to give carbocation 21 which can also cyclize to afford pyran 7. The second photoreaction is the photocyclization reaction of 2- phenoxybenzyl alcohols 22 and 23 to give dibenzo[b,d]pyrans 7 and 29, respectively, in aqueous solution. The primary photochemical step is believed to involve initial aryl-O bond homolysis followed by rearrangement to give alcohol 1, which cyclizes to observed pyran 7 upon secondary photolysis. The meta-substituted isomer 24 did not produce cyclized photoproducts, but instead gave isomeric hydroxybiphenyls which are also derived from initial aryl-O bond homolysis followed by simple radical recombination. The photocyclization appears to be general for the ortho-phenoxybenzyl alcohol system, in which an appropriate assembly of phenoxy and hydroxymethyl (CH2OH) functional groups is a necessary requirement. In acidic solution, a competing proton-assisted photosolvolysis reaction, via heterolysis of the benzylic C-OH bond, takes place for all these compounds, to give carbocation intermediates which were subsequently trapped by the solvent. The last reaction is the photoisomerization of xanthene (26) to pyran 7 (~70% yield and Φp ~ 0.0035 in aqueous solution). In addition to 7, 2- benzylphenol (40) (Φ = 0.001), 9,9’-bixanthyl (41) (Φ < 0.001) and alcohol 1 (Φ < 0.001) were also observed as minor products in the reaction. The photoisomerization is again initiated by aryl-O bond homolysis in S1, to give a singlet phenyl/phenoxy biradical 48 which undergoes a radical ipso-attack on the adjacent phenyl ring, followed by rearrangement to afford o-quinonemethide 20, which cyclizes to form pyran 7 in competition with nucleophilic solvent capture to give 5 (by MeOH). Xanthene derivative 42 also photoisomerizes to the corresponding pyran derivative 29, which was obtained in much lower yield due to secondary photochemistry of 29. / Graduate

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The photodebromination of selected bromoarenes has been studied at 300 nm to determine the the possible mechanistic pathways leading to product. Irradiation of 4-bromobiphenyl (BpBr) at this wavelength leads to the product biphenyl. The quantum yield of intersystem crossing (0.98) and quenching studies with cis-1 ,3-pentadiene suggest that the reaction occurs only via the triplet state. The observed increase of quantum yield of reaction with increasing concentration of BpBr suggests formation of a triplet excimer between the triplet state and ground state of BpBr as the key reactive intermediate. The log of the rate constant for excimer formation showed a linear increase with solvent polarity. The correlation of rate constants for excimer formation with linear solvation energy parameters indicates only a weak polarization of the excimer species. In order to understand the extent of radical anion character in the excimer, the regiochemistry of the photo-debromination of 3,4-dibromobiphenyl (3,4-BpBr) was studied. 3,4-BpBr was irradiated with and without an electron donor (triethylamine). 3,4-BpBr was also chemically reduced with lithium biphenylide (LiDBB). The difference in the regiochemistries under these conditions has been interpreted in terms of reaction via a free radical anion in the case of reactions with triethylamine and LiDBB and a weakly polarized excimer in the case of direct irradiation. In order to understand the extent of polarization in the excimers and their conformation, it was decided to study systems where the structure of the molecule would fix the geometry of potential intramolecular charge-transfer complexes. Towards this goal, brominated [2.2]paracyclophanes, 4-bromo[2.2]para-cylophane (CpBr), pseudo-para-dibromo[2.2]cyclophane (ps-p-CpBr) and pseudo-ortho-dibromo[2.2]cyclophane (ps-o-CpBr), were studied. The effect of substitution pattern of the bromines on the efficiency of excimer formation was also investigated. The brominated [2.2]para-cyclophanes showed varying efficiencies of formation of intermolecular excimer and intramolecular charge-transfer. A probable conformation for the excimer from BpBr has been proposed based on these results. / Graduation date: 1991

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A decomposição catalisada de 1,2-dioxetanos contendo substituintes doadores de elétrons protegidos ocorre através do mecanismo CIEEL (Chemically Initiated Electron Exchange Luminescence) intramolecular e leva à formação eficiente de estados eletronicamente excitados singlete. Estes compostos estão sendo utilizados em uma grande variedade de métodos analítico-bioquímicos. Os dioxetanos 3,3-dimetil-4-(4-metóxi-fenil)-1,2-dioxetano (I), 3-(4-(tbutil-dimetil-sililóxi)-fenil-4,4-dimetil-1,2-dioxetano (II), 3,3-dimetil-4-(4-metóxi-benzil)-1,2-dioxetano (III) e 3-(4-(tbutil-dimetil-sililóxi)-benzil)-4,4-dimetil-1,2-dioxetano (IV) foram sintetizados, caracterizados e tiveram as suas propriedades quimiluminescentes estudadas. Estes dioxetanos possuem substituintes fenólicos protegidos por grupos metila ou trialquilsilila, diretamente ligados ao anel peroxídico ou distantes deste por um grupo metilênico. Embora os rendimentos quânticos obtidos na decomposição iniciada por íons fluoreto de II e IV sejam consideravelmente mais baixos que os dos análogos meta substituídos, os parâmetros de ativação mostraram-se bastante similares. Os baixos rendimentos quânticos obtidos com II e IV em comparação com os dos derivados meta substituídos podem ser explicados através do \"efeito meta\" descrito na literatura e demonstram também que no caso de IV, apesar da presença da ponte metilênica, existe uma \"conjugação\" entre o grupo fenólico e o anel peroxídico. / The catalyzed decomposition of 1,2-dioxetanes containing protected electron donor substituents occurs by intramolecular CIEEL (Chemically Initiated Electron Exchange Luminescence) and leads to the efficient formation of electronically excited singlet states. These compounds are employed in a wide variety of analytical biochemical methods. The dioxetanes 3,3-dimethyl-4-(4-methoxy-phenyl)-1,2-dioxetane (I), 3-(4-(tbutyl-dimethyl-silyloxy)-phenyl-4,4-dimethyl-1,2-dioxetane (II), 3,3-dimethyl-4-(4-methoxy-benzyl)-1,2-dioxetane (III) e 3-(4-(tbutyl-dimethyl-silyloxy)-benzyl)-4,4-dimethyl-1,2-dioxetane (IV) were synthesized, characterized and its chemiluminescent properties studied. These dioxetanes contain phenolic substituents, protected by methyl and trialkylsilyl groups, directly linked to the peroxidic ring or distanced from it by a methylene moiety. Although the quantum yields obtained in the fluoride initiated decomposition of II and IV are considerably lower than of the meta substituted analogs, the activation parameters proofed to be quite similar. The low quantum yields obtained for li and IV, in comparison to the meta substituted derivatives, can be explained by the \"meta effect\" described in the literature and demonstrate that conjugation between the phenolic group and the peroxidic ring exists also in the case of IV, in spite of the presence of the methylene bridge.

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

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Thesis (Ph. D.)--State University of New York at Binghamton, Chemistry Department, 2005. / Includes bibliographical references.