Photocatalytic reactions of tin diphthalocyanine, Sn ^IVPc₂ and anionic form of Nd^III, Dy^III, Eu^III, Tm^III and Lu^III diphthalocyanine complexes ( [Pc(-2)Nd^IIIpc(-2)]⁻ , [Pc(-2)Dy^IIIPc(-2)]⁻ , [Pc(-2)Eu^IIIPc(-2)⁻, [Pc(-2)Tm^IIlPc(-2)r and [Pc(-2)LuIIIpc(-2)]⁻ respectively) in the presence of CH₂CI₂, S0₂, pentachlorophenol (PCP), 4-chlorophenol (4-Cp) and thionyl chloride have been studied. Photoreactions involving lanthanide diphthalocyanines, filtered and unfiltered radiations were employed, whereas for photoreactions involving tin diphthalocyanine, only unfiltered radiation was employed. For lanthanide diphthalocyanine complexes, LnPce-, the photosensitization power increases with the decrease of the lanthanide ionic radii, implying that the photocatalytic activity of LnPc₂⁻ complexes is associated with the π-π interaction between both phthalocyanine rings. Thus, LuPc₂⁻ is a better photocatalyst than other lanthanide diphthalocyanine complexes. Photolysis ofSnPc₂ in an acetonitrile/dichloromethane solvent mixture, using unfiltered radiation from a tungsten lamp, results in the one-electron oxidation of this species to [Pc( -2 )Sn(IV)Pc(-1)]⁻. The relative quantum yields for the disappearance of SnPc₂ are in the order of 10⁻¹. The photoreaction of SnPc₂ is preceded by excitation to nπ* excited states, before been ,quenched by CH₂CI₂. The one-electron oxidation species, [Pc(-2)Sn(lV)pc(-1)]⁻ was also formed during the photolysis of SnPc₂ in dichloromethane containing S0₂, and with quantum yields of order of 10⁻³. Visible photolysis of [Pc( -2)Nd^IIIpc(-2)]⁻, [Pc(-2)Dy^IIIPc(-2)]⁻ and [Pc(-2)Lu^IIIpc(-2)]⁻ in N,N. dimethylformamide (DMF)/dichloromethane solvent mixture containing SO₂, results in the formation of the one-electron oxidation species, Pc(-2 )Nd^IIIpc(-1), Pc( -2) Dyi^IIIPc(-1) and Pc(-2)Lu^IIIpc(-1), respectively. The relative quantum yields are in the order of 10². The photoreactions are preceded by population of the excited triplet state,³π-π* [ LnPc₂]⁻ complex, before exchanging an electron with S0₂. The one-electron oxidation species of Dy^III and Lu^III diphthalocyanine complexes have also been formed from visible photolysis of [Pc(-2 )Dy^IIIPc(-2)]⁻and [Pc(-2)Lu^IIIpc(-2)]⁻in acetonitrile containing PCP. The PCP is reductively dechlorinated to tetra- and trichlorophenols. The quantum yields for the photosensitization reactions are in the order of 1 0⁻. Photolysis, using visible radiation from 220 W Quartzline lamp, of an aqueous solution of 4-Cp, saturated with oxygen and containing a suspension of solid [Pc(-2)Nd^IIIpc(-2)]⁻, results in the formation of benzoquinone, hydro quinone and 4-chlorocatechol. The quantum yields for the degradation of 4-Cp are in the order of 10⁻. Langmuir-Hinshelwood kinetic model shows the adsorption of 4-chlorophenol onto solid [Pc(-2)Nd^IIIpc(-2)]⁻. Lanthanide diphthalocyanine complexes ([Pc-2)Nd^IIIpc(-2)]⁻. [Pc(-2)Eu^IIIpc(-2)]⁻, (Pc(-2)Tm^IIIpc( -2)]⁻ and (Pc(-2)Lu^IIIpc(-2)]⁻) undergo one or two-electron oxidation in the presence of thionyl chloride. At low concentrations of SOCI₂(<10⁻⁴ mol dm⁻³) the visible yhotolysis of [Pc(-2 )LnPc(-2)]⁻ complexes result in the one-electron oxidation, giving neutral lanthanide diphthalocyanine species, Pc(-2)Ln^IIIpc(-1). The Pc(-2 )LnPc(-I) species undergoes one-electron photooxidation to [Pc(-I )LnPc( -I)]⁻ in dichloromethane and in the presence of SOC₁₂. At large concentrations of SOC₁₂ (>10⁻² mol dm⁻³), direct two-electron oxidation of the (Pc(-2 )LnPc - 2)]⁻ species to (Pc(-1)LnPc(-1)]⁻ occurs. Spectroelectrochemical behaviours of Sn^IVPc₂ have been also studied. The cyclic voltammetry ofSnPc₂ in CH₂CI₂/TBAP show two reduction couples at -0.56 V and -0.89 V versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE. In DMFITEAP system, the reduction couples are observed at -0.44 V and -0.81 V versus SCE whereas the oxidation couple occurred at 0.43 V versus SCE. The oxidation couple corresponds to [Pc(-2 )Sn^IVPc(-2 )]/[Pc(-2)Sn^IVPc( -I)] . and the reduction couples to [Pc(-2)Sn^IVPc( -2 )]/[Pc(-2 )Sn^IVPc( -3 )]⁻ and [Pc(-2)Snl^IVPc( -3)] ⁻/[Pc(-3 )Sn^IVPc(-3)]²⁻, respectively. The electronic absorption spectra of these reduced and oxidized species are reported.

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

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

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This thesis describes the study of a variety of nanoscale materials and the development of novel synthetic strategies for their production. While the focus and bulk of this study have been directed specifically at subwavelength lithography, a significant portion of this thesis research involves nanoparticle synthesis, characterization, and functionalization. Put in very simple terms, optical lithography is a process where a beam of light, focused in a specific pattern, is used to generate a physical pattern on a solid substrate. This technology forms the basis for almost all microchip production in the world at the present time. As demand for faster and more powerful chips increases, the need to further miniaturize the patterns while minimizing cost has become very important. Multiple photochemical systems were developed in the search for non-reciprocal photochemistry at 193 nm to increase the resolution of lithographic processes at that wavelength. One approach, based on anthracene sensitization of sulfonium salts for acid generation, used photochemically reversible 4+4 aromatic cycloaddition reactions to introduce the non-linear photochemistry. A second approach took advantage of the photochemistry of N-methylphenothiazine and provided the first true example of a lithographically-relevant multi-photon acid generating process. Since all of the systems we studied used sulfonium salts as the acid generating species, we also looked at the photochemistry of the salts themselves. We evaluated the structural effects of the salts on their direct photochemistry and the implications for sensitized multi-photon photochemistry. We found that the identity of the anion plays a significant role in both processes and propose a new photochemical mechanism for acid generation that involves a charge transfer excitation process. We also describe the synthesis and characterization of novel fluorescent silver nanoparticles, both in solution and polymer films. We show that the fluorescent images can be patterned easily and preliminary results show that photolithography based on nanoparticle formation may be possible. This latter approach could provide a facile route to nanoparticle-embedded functional materials. This work with nanoparticles was inspired partly by earlier work, also presented herein, on semiconductor nanoparticles and their interactions with disulfide ligands.

Nanomaterials have become a popular topic of research over the years because of their many important applications. It can be a challenge to stabilize the particles at a nanometer size, while having control over their surface features. Copper nanoparticles were synthesized photochemically using a photogenerated radical allowing spatial and temporal control over their formation. The synthesis was affected by the stabilizers used, which changed the size, dispersity, rate of formation, and oxidation rate. Copper nanoparticles suffer from their fast oxidation in air, so copper-silver bimetallic nanoparticles were synthesized in attempts to overcome the oxidation of copper nanoparticles. Bimetallic nanoparticles were synthesized, but preventing the oxidation of the copper nanoparticles proved difficult. One important application of nanoparticles that was explored here is in catalyzing organic reactions. Because of the fast oxidation of copper nanoparticles, silver nanoparticles were synthesized photochemically on different supports including TiO2 and hydrotalcite (HTC). Their catalytic efficiency was tested using alcohol oxidations. Different silver nanoparticle shapes (decahedra and plates) were compared with the spheres to see the different catalytic efficiencies.

This thesis describes the photochemical synthesis of silver nano particles, several ways to make these particles as well as control the size and shape of the colloidal particles. Understanding the primary reactions in photochemical nanoparticle formation has lead to important contributions to the overall mechanism of metal nanoparticle synthesis. The size and shape control of the particles is shown to have important implications for the Raman spectrum of surface bound molecules. The particles have also been used in antibacterial properties where it was shown that silver nanoparticles are more antibacterial than the corresponding silver cation, while remaining non-toxic to several common cell lines. The particles were also shown to have some interesting properties that can be exploited in lithography and optoelectronics.

Metastable, electronically excited atoms (²Dº , ²Pº ) of phosphorus, arsenic and antimony have been observed following the isothermal flash photolysis of Group VA hydrides and trihalides. Several mechanisms for the production of these atoms are discussed. The decay of the excited atoms was observed to be rapid due to reactions with the transients produced in the flash photolysis of the parent compounds. Flash photolysis of the Group VA hydrides and trichlorides has yielded new electronic absorption spectra of the AsH and AsH₂, SbH and SbH₂, PC1, AsC1, and SbC1 free-radicals. Vibrational analysis on some of these spectra have been carried out. In the isothermal flash photolysis of cyanogen with Group VA hydrides, it is proposed that the following reactions of the cyanogen radical occur rapidly: CN + AH₃ → AH₂ + HCN (1) CN + AH₂ → AH + HCN (2) CN + AH → ACN + H (A=N,P,As) (3) → HCN + A* (A=P,As, Sb) (4) (formula omitted) HACN (A=N,P) (5) where A, unless specified, is N, P, As or Sb and * denotes electronic excitation. Three of the new electronic absorption spectra observed are tentatively attributed to the PCN, HPCN and AsCN free-radicals produced in reactions (3) and (5). The assignment of the other spectra is discussed. Reactions of CN with NF, PC1 and AsC1, corresponding to (3), have also been shown to occur rapidly. The reactions of the cyanogen radical in the flash photolysis of cyanogen with nitrous oxide, oxygen, water, and methyl isocyanate have also been studied and discussed. / Science, Faculty of / Chemistry, Department of / Graduate

CO2 is generally regarded as a waste product. However, the efficient catalytic reduction of CO2 means that this concept can change to viewing this molecule as a feedstock to produce chemically valuable products. The catalytic reduction of CO2 is a challenge because of its stability, and its reduction into chemically valuable products requires an appropriate catalyst and accessible energy source. While second and third row transition metals have shown considerable promise as photocatalysts for the reduction of CO2 to CO, one of our goals is to elaborate on the metal centers and the ligand environments in order to discover new catalysts and processes. These efforts have revealed new photocatalysts based on manganese and rhenium supported by κ2-PN phosphinoaminopyridine ligands. This thesis will describe the synthesis and characterization of these catalysts and their CO2 reduction parameters. The selectivity of these catalysts for either CO or HCOOH will be explored. Furthermore, ligand modifications and their effects on the catalyst behaviour will also be presented.

Solar ultraviolet-B (UVB) radiation is capable of converting 7-dehydrocholesterol (7-DHC) to previtamin D3 (preD3), which undergoes thermal isomerization to produce vitamin D3. Further ultraviolet irradiation of preD3 will produce other photoproducts, including lumisterol3, tachysterol3, and 7-DHC. Continued exposure to UVB results in a photoequilibrium of these photoproducts. During the winter months, people living at latitudes greater than 32° north or south are incapable of converting cutaneous 7-DHC to preD3. Because an increased zenith angle creates a longer path-length for UVB radiation to traverse through the atmosphere, ozone can absorb a much greater proportion of this radiation. Given the absorption spectrum of tachysterol3 which absorbs UV radiation up to 340nm, it was hypothesized that winter sunlight which contains UV radiation between 315nm and 340nm would be able to convert tachysterol3 to preD3. Each hour between sunrise and sunset, ampules containing 50g/mL tachysterol3, lumisterol3, and 7-DHC in 100% ethanol were exposed to solar radiation. These samples were chromatographed on a normal phase chromatographic column. Results revealed that tachysterol3 was efficiently converted to preD3 from sunrise to sunset, whereas as 7-DHC and lumisterol3 were not. Exposure of tachysterol3 to sunlight throughout the day revealed that tachysterol3 began converting to preD3 at sunrise at 8am and the peak conversion occurred between 10:00 and 13:00. PreD3 was generated from tachysterol3 until sunset. No preD3 was observed when 7-DHC or lumisterol3 were exposed at the same time. From this data, it is feasible to use tachysterol3 to produce preD3 in a topical preparation during winter.