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Amorphous and crystalline silicon nanocomposites have been shown to act as effective “sensitizers” for erbium ions. In the present work, a series of erbium-doped (0.2 at.%) SiOx:Er films (x = 1 - 1.8) were synthesized by physical vapor deposition and subsequently annealed at temperatures ranging from 400°C to 1100°C to induce phase separation and cluster growth. Silicon nanocluster (Si-NC) and Er3+ photoluminescence intensity spectra and dynamics were investigated as a function of SiOx composition, annealing temperature, pump wavelength and power, and specimen temperature in order to determine characteristic cross-sections and to map the efficiency of the energy transfer process between Si-NCs and Er3+ ions. Additionally, two types of optical waveguides based on SiOx:Er materials were fabricated using conventional CMOS compatible microfabrication processes. Waveguide propagation losses as well as signal absorption and enhancement were investigated under pumping conditions to evaluate the use of SiOx:Er materials as amplifying media. / Communications and Signal Processing

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Interações do estado fundamental e espécies transientes, formadas após fotólise e fotossensibilização de 2-ethylaminodiphenylborinate (2APB) e diphenylboronic anhydride (TPhB), foram estudadas por várias técnicas. Os espectros UV mostram uma grande banda de absorção na região do Ultra-violeta. Os espectros de fluorescência mostram o aumento da intensidade de emissão, em 300 nm, que se desloca para o vermelho até 10-3 M. Em concentrações mais elevadas, a intensidade de emissão diminui, provavelmente devido à formação de agregados. Excitação dos organoboranos no UV, em soluções livre de oxigênio, mostram a formação de dois transientes em 300 e 360 nm. Este último, atribuído a espécie triplete, tem uma vida útil de 5 ms em etanol e é totalmente suprimida na presença de oxigênio. A banda em 300 nm não é afetada por oxigênio, tem uma vida útil da ordem de milisegundos e corresponde a uma espécie com radical centrado no boro. O radical também pode ser obtido por transferência eletrônica do estado triplete da Safranina ao organoborano, formando a forma semioxidada do corante. Experimentos EPR, usando DMPO, mostram que a fotólise direta no UV de 2ABP forma o radical arilborano, seguido pela clivagem de uma ligação B-C e formação de radicais fenil. Radicais de boro são formados quando organoboranos são fotossensíveis por Safranina. Na tentativa de se estender o uso de organoboranos em sistemas de poliméricos, sais ônium foi usado para produzir mais iniciadores e melhorar a velocidade de polimerização. Na excitação visível, induzida a produzir iniciadores, o sentitizador (corante *) é oxidado pelo organoborano para formar o cátion radical correspondente (coranteo+) e R3Bo -. Este ânion radical pode iniciar a polimerização ou interagir com sal de ônio, resultando na liberação de uma grande quantidade de radicais que inicia a polimerização mais eficiente. / Ground state interactions and excited states and transients formed after photolysis and photosensitization of 2-ethylaminodiphenylborinate (2APB) and diphenylboronic anhydride (TPhB) were studied by various techniques. The UV spectra show a large absorption band at UV-spectra. The fluorescence spectra show increasing emission intensity with maximum at 300 nm, which shifts to the red up to 10-3 M concentrations. At higher concentrations, the emission intensity decreases, probably due to the formation of aggregates. UV excitation in deareated solutions shows the formation of two transients at 300 and 360 nm. The latter has a lifetime of 5 ms in ethanol and is totally quenched in the presence of oxygen and assigned to the triplet state of organoborane. The 300 nm peak is not affected by oxygen, has a lifetime in the order of milliseconds, and corresponds to a boron-centered radical species originated from the triplet state. The radical can also be obtained by electron transfer from triplet Safranine to the borane forming the semioxidized form of the dye. EPR experiments using DMPO show that the UV-direct photolysis of 2ABP renders initially arylboroncentered radicals followed by the cleavage of a B-C bond and formation of phenyl radicals. Similar boron radicals are formed when 2APB is photosensitized by Safranine. To extend the use of organoboranes in polymeric system, ônium salts was used to produce more initiators and improve the polymerization velocity. In the visible-induced excitation to produce initiators, the sentitizer (dye*) is oxidized by trivalent and neutral organoborane compound to form the corresponding radical cation (dyeo+) and R3Bo-. This radical anion may itself initiate the polymerization or may interact with onium salt, resulting in the release of a lot of radical that can initiate the polymerization more efficiently.

Interações do estado fundamental e espécies transientes, formadas após fotólise e fotossensibilização de 2-ethylaminodiphenylborinate (2APB) e diphenylboronic anhydride (TPhB), foram estudadas por várias técnicas. Os espectros UV mostram uma grande banda de absorção na região do Ultra-violeta. Os espectros de fluorescência mostram o aumento da intensidade de emissão, em 300 nm, que se desloca para o vermelho até 10-3 M. Em concentrações mais elevadas, a intensidade de emissão diminui, provavelmente devido à formação de agregados. Excitação dos organoboranos no UV, em soluções livre de oxigênio, mostram a formação de dois transientes em 300 e 360 nm. Este último, atribuído a espécie triplete, tem uma vida útil de 5 ms em etanol e é totalmente suprimida na presença de oxigênio. A banda em 300 nm não é afetada por oxigênio, tem uma vida útil da ordem de milisegundos e corresponde a uma espécie com radical centrado no boro. O radical também pode ser obtido por transferência eletrônica do estado triplete da Safranina ao organoborano, formando a forma semioxidada do corante. Experimentos EPR, usando DMPO, mostram que a fotólise direta no UV de 2ABP forma o radical arilborano, seguido pela clivagem de uma ligação B-C e formação de radicais fenil. Radicais de boro são formados quando organoboranos são fotossensíveis por Safranina. Na tentativa de se estender o uso de organoboranos em sistemas de poliméricos, sais ônium foi usado para produzir mais iniciadores e melhorar a velocidade de polimerização. Na excitação visível, induzida a produzir iniciadores, o sentitizador (corante *) é oxidado pelo organoborano para formar o cátion radical correspondente (coranteo+) e R3Bo -. Este ânion radical pode iniciar a polimerização ou interagir com sal de ônio, resultando na liberação de uma grande quantidade de radicais que inicia a polimerização mais eficiente. / Ground state interactions and excited states and transients formed after photolysis and photosensitization of 2-ethylaminodiphenylborinate (2APB) and diphenylboronic anhydride (TPhB) were studied by various techniques. The UV spectra show a large absorption band at UV-spectra. The fluorescence spectra show increasing emission intensity with maximum at 300 nm, which shifts to the red up to 10-3 M concentrations. At higher concentrations, the emission intensity decreases, probably due to the formation of aggregates. UV excitation in deareated solutions shows the formation of two transients at 300 and 360 nm. The latter has a lifetime of 5 ms in ethanol and is totally quenched in the presence of oxygen and assigned to the triplet state of organoborane. The 300 nm peak is not affected by oxygen, has a lifetime in the order of milliseconds, and corresponds to a boron-centered radical species originated from the triplet state. The radical can also be obtained by electron transfer from triplet Safranine to the borane forming the semioxidized form of the dye. EPR experiments using DMPO show that the UV-direct photolysis of 2ABP renders initially arylboroncentered radicals followed by the cleavage of a B-C bond and formation of phenyl radicals. Similar boron radicals are formed when 2APB is photosensitized by Safranine. To extend the use of organoboranes in polymeric system, ônium salts was used to produce more initiators and improve the polymerization velocity. In the visible-induced excitation to produce initiators, the sentitizer (dye*) is oxidized by trivalent and neutral organoborane compound to form the corresponding radical cation (dyeo+) and R3Bo-. This radical anion may itself initiate the polymerization or may interact with onium salt, resulting in the release of a lot of radical that can initiate the polymerization more efficiently.

Ultraviolet A is a major spectral component of solar electromagnetic energy reaching the surface of the earth. Excessive exposure to solar UVA is a known contributor to skin photoaging and photocarcinogenesis, associated with increased incidence rates and a significant health burden imposed by skin cancer worldwide. However, the molecular mechanisms underlying UVA-induced skin photodamage remain largely undefined. UVA radiation has been shown to cause cutaneous oxidative stress and photosensitization reactions involving the light-driven photochemistry of specific skin chromophores upstream of reactive oxygen species formation, recognized as key players in skin photooxidative damage. Consequently, there has been significant interest in the identification of endogenous compounds that facilitate these reactions serving as endogenous photosensitizers. In my graduate research, we assessed the potential of selected endogenous chromophores, pyridoxal and 6-formylindolo[3,2-b]carbazole (FICZ), to elicit UVA-induced photo- and genotoxicity in relevant models of human skin, and further identified the underlying molecular mechanisms involved. We demonstrated for the first time that the B6-vitamer pyridoxal, previously shown to contain the phototoxic 3-hydroxypyridine moiety, is a micromolar sensitizer of UVA-induced genotoxicity in human primary keratinocytes and human epidermal reconstructs, which may be relevant to human skin exposed to high concentrations of B6-vitamers. Additionally, we have demonstrated that FICZ, a tryptophan photoproduct and endogenous high-affinity aryl hydrocarbon receptor (AhR) agonist, as the most potent endogenous UVA- and visible light-activated photosensitizer identified as of today. FICZ potentiates photooxidative stress, an effect that occurs independent of AhR ligand activity. Given the extraordinary photodynamic potency of FICZ, which surpasses that of any known endogenous photosensitizer, including protoporphyrin IX, and its rapid metabolic turnover, we tested the feasibility of using FICZ for the photodynamic elimination of malignant skin cancer cells in vitro and in vivo. Indeed, light photoactivation of FICZ-induced phototoxidative damage and cytotoxicity in a panel of cultured human malignant skin cells, and furthermore suppressed post-UVB tumorigenic progression in high-risk SKH-1 mice. Based on these pilot studies, follow up experiments will further optimize FICZ-based photodynamic interventions targeting human skin malignancies in relevant model systems. In pursuit of minimizing the need for invasive therapeutic methods, exploitation of stress response pathways has become a topic of interest for interventions aimed at the eradication of skin cancer at early or late progressional stages. Therefore, we tested feasibility of harnessing the cellular metal stress response for the elimination of skin cancer cells using the zinc-ionophore and FDA-approved microbicidal agent zinc pyrithione (ZnPT). Indeed, in a panel of cultured malignant skin cancer cells it was observed that ZnPT treatment caused rapid intracellular zinc overload and redox dysregulation, followed by a loss of genomic integrity and induction of caspase-independent cell death. In a murine photocarcinogenesis model, chronic topical ZnPT-administration post-UV caused epidermal zinc-overload and stress response gene expression with pronounced blockade of tumorigenic progression. These data suggest the feasibility of repurposing a topical OTC-drug for zinc-directed photochemoprevention of solar UV-induced nonmelanoma skin cancer. In summary, these studies contribute to our mechanistic understanding of photosensitizer- and zinc-induced stress responses in human skin, and furthermore provide the molecular basis for innovative therapeutic strategies aimed at the elimination of skin cancer cells.

A common characteristic of all chemical allergens, both respiratory and skin allergens, is the ability to form stable associations with proteins; the resulting hapten-protein complex being sufficient to provoke an immune response. There is evidence to suggest that selective binding of chemicals with proteins or peptides may impact on the quality of immune response that will develop. In the investigations described here, we have taken a reductionist approach to protein reactivity and evaluated the binding characteristics of 20 of the most commonly reported chemical respiratory allergens towards defined peptides with a single reactive amino acid of interest. The hypothesis is that it is possible to identify and characterize different forms of chemical allergens as a function of preferential peptide binding.Utilizing the standardized reaction conditions of a direct peptide reactivity assay (DPRA), the reactivity of respiratory allergens for cysteine and lysine peptides was evaluated. Activity in the DPRA is reported as the percent depletion of peptide following 24 h incubation. An important and intriguing observation was that, when compared with skin sensitizers, chemical respiratory allergens exhibited a preferential reactivity for lysine. This preference was characterized quantitatively as a ratio of the mean depletion of lysine compared with cysteine (Lys:Cys ratio). The Lys:Cys ratio was observed to be robust and reproducible over time.A limitation of many in chemico methods for hazard identification is the lack of a metabolic component that allows for the identification of pro-haptens. In order to address this limitation, reported here is the use of the peroxidase peptide reactivity assay (PPRA), which utilizes a horseradish peroxidase/hydrogen peroxide (HRP/P) enzymatic system as a proxy for oxidative metabolism. Additionally, reactivity in the PPRA is characterized after a 24 h reaction time utilizing a concentration-response model (thus, permitting consideration of dose-response relationships defined as an EC15 value). Unexpectedly, the preferences for lysine observed with chemical respiratory allergens in the DPRA were lost or blunted in PPRA. The EC15 values demonstrated that relative reactivity between chemical respiratory allergens varied by up to 4 orders of magnitude. The identification of quantitative differences in reactivity could prove useful as a guide to evaluate potency in the future, should reliable metrics become available.To characterize the selectivity of binding by chemical respiratory allergens, the DPRA was modified to allow for the evaluation of reactivity to histidine, tyrosine and arginine. Confirming our previous observations, each of the respiratory sensitizers was observed to react to both lysine and cysteine, with in most instances, a preference for the former. Reactive promiscuity was a function of the other peptides with histidine being the most reactive followed by arginine and tyrosine. To model more complex reactive conditions, a novel modification was made to the DPRA to allow competition for lysine and cysteine to be assessed in a single reaction mixture. The results of these competitive reactivity experiments identified a range of binding patterns to lysine and cysteine that in some cases resulted in different binding being expressed.At present, there are no methods available to reliably identify potential chemical respiratory allergens. The work presented here has demonstrated that respiratory allergens can be identified as potential sensitizers based on their ability to react with lysine and cysteine. More importantly, the balance of reactivity to these two peptides can provide a means of discriminating between respiratory and skin sensitizers.

About 85% of the world’s energy is derived from non-renewable sources—coal, petroleum, and natural gas. Solar photocatalysis is one way to potentially generate renewable fuels. Zinc dipyrrin complexes have the potential to be efficient sensitizers for reductive photochemistry, but their ability to form long-lived triplet excited states needs further investigation. The overall aim of this research is to compare the photophysical properties zinc and boron dipyrrin complexes and investigate the role of the charge separated state in triplet state formation. This presentation will describe the synthesis and purification of zinc and boron dipyrrin complexes and their photophysical characterization, including fluorescence quantum yields in a series of solvents and their emission at low temperatures.

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