Browsing by Subject "Porphyrin"

Now showing 1 - 8 of 8
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    Design, Synthesis, And Characterization Of Aluminum(Iii) Porphyrin Assemblies For Use In Photochemical Cells
    (2020-05) Boe, Benjamin
    A series of axially-coordinated aluminum(III) porphyrins were synthesized and evaluated as potential photosensitizers of a ruthenium-based water oxidation catalyst. The porphyrins themselves are 5,10,15,20-tetraphenylporphyrins, and differ in the degree of fluorination on the peripheral phenyl groups. These aluminum(III) porphyrins readily assemble into catalytic dyads through formation of a covalent ester linkage between the central aluminum atom of the porphyrin and a terminal carboxyl group on the ruthenium catalyst. The aluminum center is also able to act as a Lewis acid, forming the final triad by way of a coordinate bond with a suitable Lewis base. Catalytic dyads were successfully synthesized from all three porphyrins in the series; a set of control compounds were also prepared. The dyads and reference molecules were then characterized, with molecular structure and successful formation of the dyads being confirmed with proton NMR spectroscopy, optical properties assessed with respect to UV-Vis absorption and fluorescence spectroscopy, and redox potentials being assessed by both cyclic and differential pulse voltammetry. Formation of the final triad was achieved by titration of the catalytic dyads with a C60 fullerene functionalized to act as a Lewis base; absorption and fluorescence spectra were monitored during titration, allowing for confirmation of the triad formation, as well as calculation of binding constants. The characterization data were used to construct energy level diagrams, laying the groundwork for a theoretical abstraction of these molecule’s functioning. the catalytic systems as synthesized, as well as how they might function in a prototypical photochemical cell. ii Analysis of the results reveal these materials to be promising candidates as photoactivated water oxidation catalysts. The absorption and electrochemical data demonstrate that, when the catalytic dyads are formed, the electronic structure of the constituent parts is preserved. The fluorescence spectra of the dyads show significant quenching relative to the reference porphyrins. Control studies allowed for the exclusion of intermolecular processes as being the source of this quenching, and therefore the optically excited porphyrin must be able to interact with the attached ruthenium catalyst, either through energy or electron transfer. Based on the negligible overlap of the spectra of the catalyst with that of the porphyrins, energy transfer is unlikely. The most likely source of the fluorescence quenching is therefore electron transfer across the ester-bond. The formation and persistence of such a radical ion pair is a fundamental prerequisite for the material to function as a water oxidation catalyst, as it is on this charge-separated species that water oxidation proceeds. Coordination of the dyads with a fullerene ligand was similarly demonstrated, with the resulting triad exhibiting complete fluorescence quenching. The fullerene ligand itself was chosen specifically for its suitability as an electron acceptor, and once again the most likely cause of this quenching is intramolecular electron transfer.
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    Design, Synthesis, and Characterization of Novel Photosensitizers for Use in Molecular Machines
    (2021-08) Bayard, Brandon
    Phosphorus porphyrin-naphthyl compounds were synthesized and evaluated for future use as an electron acceptor/donor system within a photoactivated molecular shuttle. This evaluation consisted of characterizing the redox and optical properties of the systems, as well as determining the formation constant of the complex formed between the naphthyl group in each compound and a previously reported macrocycle, cyclobis(paraquat-p-phenylene) (CBPQT), with affinity towards various naphthyl derivatives. This data was holistically reviewed and used to evaluate the potential use of phosphorus porphyrin-naphthyl compounds as an electron donor/acceptor system within a molecular shuttle. Furthermore, an informed design for such a molecular shuttle was produced, and steps towards its synthesis were taken. Two other projects in which novel photosensitizers were synthesized and characterized are detailed here. The purpose of these two projects is to extensively identify their optical and redox properties such that they may be used in future systems such as molecular machines or artificial photosynthesis. The first project explores a series of phosphorus tetraphenylporphyrin derivatives in which the phenyl rings of the porphyrins have various amounts of methoxy groups adorning them. The second project explores a novel phosphorus porphyrin/aluminum porphyrin heterodimer. The goal of which is to characterize the interactions of the chromophores when no exciton coupling is observed.
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    Engineering light-energy conversion into nonphotosynthetic hosts
    (2013-12) Tikh, Ilya
    Over billions of years photosynthetic organisms have refined the molecular machinery required for the capture and conversion of light into chemical energy. To date, much research has been devoted into harnessing this unique trait from photosynthetic organisms and utilizing them for ecologically clean production of valuable resources, such as alternatives to fossil fuels or commodity chemicals. Unfortunately, photosynthetic organisms are not always ideal host for the production of desired chemicals and are frequently difficult to engineer. In order to bypass those hurdles, this work focused on introducing the machinery responsible for the light-energy conversion into a nonphotosynthetic host. The supplementation of a heterologous host with the energy captured via the light-energy conversion could alleviate some of the host's metabolic burden and allow for greater yields of desired compounds. In order to achieve our goals, we set out to engineer functional expression of the bacterial reaction center from R. sphaeroides as well as the enzymes required for the production of bacteriochlorophyll into E. coli. For the first time we were able to demonstrate the expression of the reaction center complex as well as its primarily polar localization with E. coli cells. Furthermore, we characterized two previously poorly understood enzymes involved in the production bacteriochlorophyll, the 8-vinyl reductase (BciA) and the Mg protoporphyrin monomethylester cyclase (BchE). In the case of BciA, we showed that unexpectedly the BciA from R. sphaeroides was not functional when expressed in E. coli, unlike the BciA from C. tepidum. At the beginning of this work, BchE was the only enzyme involved in the biosynthesis of bacteriochlorophyll that has not been heterologously expressed and had no published biochemical or biophysical data. Through our efforts, we were able to demonstrate that BchE contained an oxygen sensitive 4Fe-4S cluster able to interact with SAM, the predicted co-factor. Additionally, for the first time, we showed the interaction of BchE with several intermediates of the bacteriochlorophyll biosynthetic pathways. Complementary to our efforts, we also produced a set of protein expression vectors for use in R. sphaeroides. R. sphaeroides is a photosynthetic organism which has been used extensively for the production of value added compounds and has the potential to be used for the production of membrane proteins. The novel vectors are BioBrickTM compatible and contain DsRed as a reporter protein driven by the photosynthetic puf promoter. We demonstrated that by selecting which section of the promoter was utilized in combination with various culture conditions, final reporter levels could be modulated. Reporter levels ranged from virtually undetectable to higher than what is present in E. coli when expression is driven from a constitutive lac promoter from the same vector backbone.
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    Excited state dynamics of metalloporphyrins utilized in optoelectronic devices
    (2013-08) Hinke, Jonathan Arthur
    Energy consumption in the world is currently dominated by fossil fuels (85%) which include coal, gas, and oil while photovoltaics constitute a small portion (0.1%). The hotovoltaic market is primarily comprised of silicon based photovoltaics which are currently unable to compete with fossil fuels in cost per kilowatt hour. However, emerging organic photovoltaics (OPVs) have shown potential to be surpass silicon based photovoltaics and be cost competitive with fossil fuels. One of the limitations in OPVs is the short diffusion length (10 nm) relative to the absorbing layer thickness (100-200 nm). Porphyrins, of which chlorophylls are derivatives, remain at the forefront of OPV investigation due to their success in natural photosynthesis and potential in photovoltaic devices. Furthermore, platinum octaethyl porphyrin (PtOEP) has been estimated to have a diusion length between 18-30 nm and long triplet lifetime (100 microsecondss). This long diffusion length indicates that platinum porphyrins are able to efficiently funnel excitons to the interface, showing promise as suitable donor materials. Other porphyrins, such as nickel, palladium, tin, and indium show similar properties including strong absorption, enhanced excited state lifetimes, and charge separated states. This thesis investigates the excited state properties of porphyrin materials. Ultrafast pump probe spectroscopy allows for investigation of excited state dynamics including intramolecular energy transfer observed in nickel porphyrins. Femtosecond dynamics of palladium and platinum porphyrins are explored as well as triplet fusion in PtOEP neat films, providing a unique way to study energy transfer and amorphous films. Finally, pump probe studies aim to explain photoluminescent quenching behavior in tin and indium porphyrins through observation of charge separated states. Investigation of these porphyrins is crucial to improving device efficiency through fundamental understanding of the excited state dynamics in films and neat films.
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    Synthesis and characterization of ferrocenyl-containing porphyrins and tetraazaporphyrins
    (2013-08) Purchel, Anatolii
    Nano-sized molecular-based platforms provide a promising approach to materials which can be used in optoelectronics, switchable redox-driven devices, and dye-sensitized solar cells (DSSC), as well as other technological applications. Poly(ferrocene)-containing compounds with accessible mixed-valence properties at low potentials and broad absorption spectra in the UV-vis-NIR region represent an important class of organometallics which have potential for use in light-harvesting, photocatalysis, and molecular electronics. Target compounds were prepared using previously developed procedures, and characterized using UV-vis-NIR, MCD, and NMR methods. A variety of solvents and electrolytes were used to investigate the redox properties of these poly(ferrocene)-containing porphyrins and tetraazaporphyrins analogues in order to determine their influence on long-range metal-metal coupling. The spectroscopic signatures of the redox-active species were investigated using spectroelectrochemical methods which were well correlated with Density Functional Theory calculations. The mixed valence properties and electronic communication observed in obtained compounds relate to those desired in molecular electronics applications and for use in DSSC's.
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    Synthesis and characterization of ruthenium (II) tetraphenylporphyrin with redox active axial ligands for molecular wires
    (2016-05) Fathi Rasekh, Mahtab
    Four new ruthenium(II) tetraphenylporphyrin with redox active axially coordinated ligands including two new heterotrinuclear Fe-Ru-Fe complexes of the ruthenium(II) tetraphenylporphyrin axially coordinated with a pair of isocyanoferrocene ((FcNC)2RuTPP) or 1,1'-diisocyanoferrocene (([C5H4NC]2Fe)2RuTPP) ligands [Fc = ferrocenyl, TPP = 5,10,15,20-tetraphenylporphyrinato(2-) anion], and two new isocyanoazulene containing complexes (2-CNAz)2RuTPP ( 2-CNAz = 2-isocyanoazulene) and (6-CNAz)2RuTPP ( 6-CNAz = 6-isocyanoazulene) were synthesized and characterized by UV-vis, MCD, NMR, and FTIR spectroscopies as well as by electrospray ionization mass spectrometry and single crystal X-ray diffraction. Isolation of insoluble polymeric {([C5H4NC]2Fe)RuTPP}n molecular wires was also achieved for the first time. The redox properties of the new trinuclear (FcNC)2RuTPP and ([C5H4NC]2Fe)2RuTPP complexes were probed using electrochemical (CV and DPV), spectroelectrochemical, and chemical oxidation methods and correlated to those of the bis(tert-butylisocyano)ruthenium(II) tetraphenylporphyrin reference compound, (t-BuNC)2RuTPP, as well as (2-CNAz)2RuTPP and (6-CNAz)2RuTPP complexes. In all cases, the first oxidation process was attributed to the reversible oxidation of the RuII center. The second and third reversible oxidation processes in (FcNC)2RuTPP are separated by ~100 mV and were assigned to two single-electron FeII/FeIII couples suggesting a weak long-range iron-iron coupling in this complex. Electrochemical data acquired for ([C5H4NC]2Fe)2RuTPP complex are complicated by the interaction between the axial 1-1,1'-diisocyanoferrocene ligand and the electrode surface as well as by axial ligand dissociation in solution. Spectroelectrochemical and chemical oxidation methods were used to elucidate spectroscopic signatures of the [(RCN)2RuTPP]n+ species in solution. In both (2-CNAz)2RuTPP and (6-CNAz)2RuTPP complexes, the first oxidation process was attributed to the reversible oxidation of RuII center and the second oxidation process was assigned to the reversible oxidation of porphyrin core. The third and fourth irreversible processes were assigned to the oxidation of two isocyanoazulene axially coordinated ligands. DFT and TDDFT calculations aided in correlating spectroscopic and redox properties of complexes with their electronic structures.
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    UV-Vis and MCD Spectroscopy and TDDFT investigations into N-Confused porphyrins and properties of mono-functionalized tetraferrocenyl porphyrins in solution and on a gold surface
    (2014-08) Erickson, Nathan Robert
    N-confused porphyrin (NCP) and its externally methylated variant (MeNCP) were investigated using UV-visible and magnetic circular dichrosim (MCD) spectroscopies. In addition to evaluating the spectroscopy of the neutral compounds, the acid/base chemistry of these macrocycles was examined by the same methods. NCP exhibits two tautomeric states depending on the polarity of the solvent, and their protonation/deprotonation chemistries also differ depending on solvent polarity. DFT and TDDFT calculations were employed to evaluate the observed spectroscopic changes. Using both experimental and calculated results, we were able to determine the sites of protonation/deprotonation for both tautomeric forms of NCP. Inspection of the MCD Faraday B terms for all of the macrocycles presented in this report showed that the ΔHOMO > ΔLUMO condition is maintained in all cases and these observations were in good agreement with the DFT calculations. Various methylated N-confused tetraphenylporphyrins (MeNCTPP) were investigated using UV-Vis and magnetic circular dicrhoism (MCD) spectroscopy in polar and apolar solvents as well as the protonation and deprotonation of the compounds. The MeNCTPPs were also investigated using time-dependent density functional theory (TDDFT) methods in the gas phase. Experimentally, the MCD spectra showed that all the molecules investigated had transitions with the ΔHOMO > ΔLUMO. TDDFT results confirmed these energy gaps. TDDFT calculations also showed that nearly all low energy transitions were from the HOMO to the LUMO and LUMO+1, except in the case of 2c, 5a, and 5c. Otherwise, results show that the addition of a methyl group to the N-confused tautomer of tetraphenylporphyrin effectively regulates the proton tautomerization of the N-confused tautomer. MeNCTPPs are unaffected by the polarizability of the solvent. Two unsymmetric meso-tetraferrocenyl-containing porphyrins of general formula H2Fc3Fc(COR)P [Fc = ferrocenyl, R = -CH3 or -(CH2)5Br, P = porphyrin(2-)] have been prepared and characterized by variety of spectroscopic methods, while their redox properties were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches. Spectroscopic signature of the mixed-valence [H2Fc3Fc(COR)P ]n+ (n = 1, 3) were investigated using spectroelectrochemical as well as chemical oxidation methods and corroborated with DFT and TDDFT calculations. Inter-valence charge-transfer (IVCT) transitions in [H2Fc3Fc(COR)P ]+ were analyzed using band deconvolution analysis in the borders of Hush model. The resulting data from the mixed-valence [H2Fc3Fc(COR)P ]+ derivatives matched very closely to the previously reported MTFcP and metal-free poly(ferrocenyl)porphyrins complexes and were assigned as Robin and Day Class II mixed-valence compounds. Following previous results indicating the ability of gold supported TFcP monolayers in photo-catalytic reduction of dioxygen, self-assembled monolayers (SAMs) of a thioacetyl derivative (H2Fc3Fc(CO(CH2)5SCOCH3)P) were also prepared and characterized using UV-vis spectroscopy and CV methods. Photoelectrochemical properties of SAMs in different electrolyte systems were investigated by electrochemical techniques and photocurrent generation experiments, showing that the choice of electrolyte is critical for efficiency of redox-active SAMs.
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    Zinc oxide nanoparticles: doping, Inkjet printing, and electron accepting from photoexcited porphyrin dyes
    (2013-06) Bierbaum, Andrew Joseph
    This research attempted to extend the useful applications of ZnO by investigating ZnO nanoparticles, doping ZnO nanoparticles, characterizing electron injection from dye molecules into ZnO nanoparticles, and depositing thin films of doped ZnO nanoparticles using inkjet printing. Chapter 1 describes research that produced particles ranging from 2.7 nm to 1 μm of undoped and doped ZnO. These particles were made using solution methods with zinc acetate and aluminum and gallium nitrate salts as dopants, and the particles were characterized by ultraviolet visible absorption, photoluminescence, infrared absorption, and transmission or scanning electron microscopy. The doped ZnO nanoparticles displayed optical signatures of doping in particles larger than 10 nm. This is significant because doping of nanoparticles is still not fully understood, and there are few examples of successfully doping nanoparticles. Chapter 2 describes the research done toward inkjet printing of ZnO films for potential use in a fully inkjet printed solar cell. The research aim was to produce a TCO film of ZnO using inkjet printing that had a bulk resistivity between 10-2 and10-3 Ω cm, a thickness between 0.1 and 1 μm, the highest transparency possible, and processed using conditions under 250 ºC. Film produced using solution methods including inkjet printing were characterized by four point probe ohmmeter, x-ray diffraction, ultraviolet visible absorption, visible microscopy, profilometry, and scanning electron microscopy. Inkjet printed films produced using nanoparticles did not meet the production requirements, but ii progress towards these goals are presented along with the successes and shortcoming of the methods used. Chapter 3 describes the research done on charge transfer from photoexcited porphyrin dyes into ZnO nanoparticles dispersions in methanol. The goal of this research was to further the understanding of the dye-semiconductor interaction and important electron transfer characteristics. Using a series of three porphyrin dyes and a range of particle sizes, the rate of electron transfer was investigated.