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Photoredox catalysis has been a flourishing field in synthetic organic chemistry. Organic chemists have been inspired by Nature and the conversion of photons into potential energy by light-harvesting biomolecules. Recent developments in photoredox catalysis have led to a rapid increase in development of new methodologies in synthetic organic chemistry. The use of transition metal photocatalysts and organic dyes in photo-mediated processes has been proven to be an effective alternative to the harsh and toxic reaction conditions that area needed in classical radical formation. Photoredox catalysis eliminates the need of initiators, stoichiometric additives, and strong oxidants, and allows for the highly efficient formation of new C-C bonds under mild conditions. Photochemistry and radical chemistry work in unison in their ability to undergo photoinduced single electron transfers (SET) or photoinduced electron transfers (PET) and enable one electron reaction pathways. A plethora of photocatalysts have been developed, mainly using Ir- and Ru-based polypyridyl complexes. Polynuclear gold complexes have come to light in the last decade as another class of photocatalysts. This bench stable complex is marked by its unique photophysical and electrochemical properties, most notable the relatively long-lived excited state. This triplet excited state can be used as a powerful reductant or oxidant when irradiated with UVA light. A class of organic substrates that can be used when working with this gold photocatalyst, is nonactivated bromoalkanes, which could not be used if working with other photocatalysts. First, the alkylative semi-pinacol using gold photoredox chemistry and nonactivated bromoalkanes was described. A new mode of reactivity of the gold binuclear photocatalyst was found where it was shown to work as a photocatalyst and a Lewis acid. Next, a follow-up to that report was the halogen atom transfer radical addition (ATRA) using gold photoredox catalysis. A mild ATRA reaction was presented where the dual reactivity of the gold photocatalyst was exploited. Mild bromine and iodine transfer reactions, without the use of strong oxidants or toxic additives, are largely unknown, and a metal-based mechanistic pathway was proposed to explain this transformation. Minisci-type alkylation is of high-interest in the field of medicinal chemistry and drug discovery. With this is mind, a photoredox catalysed Minisci reaction was presented, where the alkylation of an activated heteroarenes was achieved by HAT via chlorine atom generation. Knowing this, the alkylation using primary alcohols was presented, were a the 𝛼-alkoxy radical is formed after a HAT by chlorine atom. When secondary alcohols were used, a reduction of the heteroarene occurred and was described. Finally, a photo-mediated [3 + 2] cycloaddition using N-aryl cyclopropylamines and α, β- unsaturated carbonyl systems was described. This simple method that was presented does not require the use of photocatalysts or added additives, as it is self-catalyzed. The reaction is proceeding through a single electron transfer (SET) and offers a wide scope for the synthesis of N-arylaminocycloalkyl compounds. Overall, the collection of work described in this thesis represents the growth of photoredox catalysis in organic synthetic chemistry and the ability to form highly reactive radical without the need of harsh conditions, toxic reagents, or strong oxidants. The use of binuclear gold(I) complexes as a photocatalyst with unique photophysical and electrochemical properties was shown. Compared to Ir- and Ru-based polypyridyl complexes, which cannot react with nonactivated bromoalkanes, the binuclear gold(I) complexes offer broader redox potentials and a newfound dual mode of reactivity. Furthermore, photo-mediated synthetical useful reactions were shown. The application of photoredox catalysis in synthetic chemistry will continue to flourish, and this work is sample of all the possibilities that a simple photon can bring.

Coumarin and cinnamate derivatives were positioned as either polymer chain ends or side groups to synthesize photoactive macromolecules and gain the ability to reversibly control molecular weight and crosslink density using UV light. The cinnamates and coumarins were reacted onto the polymers via multiple reaction pathways. Polymers were functionalized with coumarin or cinnamate groups via an esterification reaction between hydroxyl functionalities and an acid chloride derivatized coumarin group. In addition to the esterification reaction, cinnamates were also coupled to polymers via a ring opening reaction between a hydroxyl functionalized cinnamate derivative and a maleic anhydride repeat unit copolymerized into the polymer. Both functional groups undergo a [2π + 2π] photodimerization reaction (coumarin groups in the UVA and cinnamate groups in the UVB), which was utilized to crosslink and chain-extend macromolecules. Coumarin dimers possess the additional ability to photocleave and thus reverse when irradiated at 254 nm. The coumarin reversible photodimerization reaction was utilized to reversibly increase the molecular weight and molecular weight distribution of coumarin-functionalized PEG monols and diols. For example, the number average molecular weight of the coumarin-functionalized PEG diol doubled and the molecular weight distribution increased from 1.08 to 2.75 when exposed to 110 J cm⁻² of UVA irradiation. Subsequent photocleavage (UVC irradiation, 2 J cm⁻²) of the chain-extended PEGs, cleaved coumarin dimers decreasing the molecular weight and molecular weight distribution to their original values. A number of poly(alkyl acrylate) and poly(methyl acrylate) systems were functionalized with coumarin groups to study the effect of the glass transition temperature and alkyl ester side group composition on the photodimerization reaction and subsequent crosslinking. The glass transition temperature (T_g) acted as an on/off switch for the photodimerization reaction. While the absolute difference between T_g and irradiance temperature did not affect the rate or extent of photodimerization reaction, polymers with a T_g greater than the irradiance temperature displayed less reaction than those with a T_g lower than the irradiance temperature. The final extent of conversion was controlled by a complex combination of factors including alkyl ester side chain steric bulkiness. Coumarin-functionalized alkyl acrylates based on ethylhexyl acrylate were tested as detachable PSAs. A 98% decrease in the adhesive peel strength was observed after exposure to UVA irradiation. Cinnamate groups were utilized in the design and synthesis of UV-curable hot melt pressure sensitive adhesives (PSAs). The cinnamate groups were attached to the PSAs to provide a method to increase molecular weight and add a small amount of crosslinking leading to an increase the adhesive strength of the PSAs. Broadband UV irradiation from a laboratory scale industrial lamp increased the peel strength of the adhesives. Postcure of the irradiated cinnamate-functionalized UV-curable hot melt PSAs was reduced compared to photoinitiated free-radical photocurable UV-curable hot melt PSAs. / Ph. D.

A method has been developed that can photoreduce polychlorinated biphenyl (PCB) to biphenyl with great speed and efficiency as well as at relatively low cost. This process uses visible light, generated by ordinary incandescent light bulbs, which is absorbed by a common dye sensitizer. The dye molecules, when excited by the absorption of light, can promote a chemical reaction between polychlorinated biphenyls and a hydrocarbon gas such as propane. In this chemical reaction, hydrogen is abstracted from the hydrocarbon gas molecule and is substituted for chlorine on the PCB molecule in a stepwise fashion, which ultimately yields the major reaction product biphenyl. This reaction occurs in a polar aprotic solvent at room temperature and is accelerated by the presence of an alkali metal hydroxide. The final residence of the chlorine appears to be a salt which precipitates from the reaction mixture. This procedure could be applied to the treatment of PCB contaminated transformer oils, soils, and landfill leachates. / M.S.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第25505号 / 工博第5272号 / 新制||工||2003(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 今堀 博, 教授 寺村 謙太郎, 教授 SIVANIAH Easan / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The development and application of photoredox methodologies in organic synthesis is a powerful paradigm in the synthesis of value-added products. While conventional methods of photoredox catalysis employ ultraviolet (UV) or blue light (i.e. visible light), the associated high energies can lead to deleterious off-cycle pathways and the formation of undesired byproducts. Transitioning to a low-energy (i.e. red/orange) light manifold can mitigate some of these challenges and promote batch-scale reactivity. We first show standardized syntheses and photophysical/electrochemical characterizations of a library of Os(II) polypyridyl complexes activatable by red light and demonstrate their application in metallaphotoredox-assisted aryl etherification. Thereafter, we leverage the advantages of spin-forbidden excitation (SFE) in the activation of novel Irⁱⁱⁱ photocatalysts, showing the first known examples of C(sp²)–C(sp³) bond formation with low-energy light. Finally, we utilize the low triplet energy and high redox versatility of an orange light photocatalyst to enable unified oxidative/reductive pathways in decarboxylative arylation, the first such photoredox system to effect dual catalytic manifolds in this paradigm with broadly similar reaction conditions.

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