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<p dir="ltr">LeadGlow (<b>LG</b>) was reported in 2009 for its ability to both sensitively and selectively detect Pb²⁺ in aqueous solutions. Utilizing the synthetic approach of <b>LG</b>, it is possible to generate a class of novel fluorophores. A derivative of first-generation <b>LG </b>was synthesized and reported here for the first time, intuitively named <b>LG2</b>. Both compounds contain interesting photophysical properties that have not been extensively researched prior to this work. Because of this, photophysical properties of both <b>LG</b> and <b>LG2</b> are unveiled here for the first time. These properties were investigated by determinations of quantum yield (QY), average fluorescence lifetime, and DFT calculations. <b>LG</b> was found to have a higher QY (0.057) than <b>LG2</b> (0.011); however, <b>LG2</b> displays an average fluorescence lifetime (3.186 ns) 5x greater than that of <b>LG</b>. Both <b>LG </b>and <b>LG2</b> are synthesized via Hg²⁺-facilitated desulfurization of their respective thiocarbonyls, resulting in a turn-on fluorescence feature. The thiocarbonyl-containing fluorophores (<b>SLG </b>and <b>SLG2</b>) display quenched fluorescence compared to their oxo-derivatives (<b>LG </b>and <b>LG2</b>), this work attempts to investigate the mechanism(s) responsible.<b> </b>A whole class of LeadGlow compounds can be synthesized and could be potentially used as fluorescence-based sensors.</p>

This paper deals with 3-picoline, 4-picoline, 3,4-lutidine and 3,5-lutidine complexes of copper(I) iodide (CuI(3-pic), CuI(4-pic), CuI(3,4-lut) and (CuI(3,5-lut)). The experimental investigation was divided into several parts. Firstly, the synthesis and characterization of the compounds both as powder and as thin films. Secondly, the photoluminescence study. Thirdly, the observation of ligand exchange reaction by vapor diffusion, and lastly, the determination of the lifetime by time-resolved photoluminescence of respective compound.  All studied copper(I)-iodide-substituted pyridine compounds were emissive both as powders and thin films. The synthesis of the tetranuclear cluster powders yields both cluster and polymeric forms of structure. The pXRD of the powders CuI(3-pic), CuI(4-pic), and CuI(3,5- lut) confirmed to be as polymeric structures, hence the CuI(3-pic) showed thermochromism behavior. The structure of CuI(3,4-lut) is still unconfirmed. The most effective method for the synthesis of the thin films was the SILAR method.  The photoluminescence spectra of respective thin films differ from their corresponding powders, and the structure of the compounds as thin films is yet unexplored. The emission of CuI(3-pic), CuI(4-pic), and CuI(3,4-lut) as thin films were similar 480nm, hence the emission of CuI(3,5-lut) thin film lays on 518 nm. Therefore, the ligand exchange reaction was performed on the CuI(3-pic) thin film with 3,5-lutidine as the exchanging ligand.  The ligand exchange reaction of CuI(3-pic) thin film by vapor diffusion of 3,5-lutidine results in a spectrum shift from the emission spectrum of CuI(3-pic) to the spectrum of CuI(3,5-lut). This indicates a successful ligand exchange reaction by vapor diffusion.  The lifetimes of the investigated compounds which have their best fit of mono-exponential function were between 2,2 μs and 9,52 μs. The lifetimes were determined on the thin films with time-resolved photoluminescence. The ligand exchange reaction was also observed by time- resolved photoluminescence which reveals some stable lifetimes during the reaction that can indicate the formation of intermediates. In contrast, the measured lifetimes during the ligand exchange reaction have their best fit of bi-exponential function which can be due to reaction conditions during the measurement or the homogeneity of the thin films. / Denna uppsats behandlar 3-pikolin, 4-pikolin, 3,4-lutidin och 3,5-lutidin komplex av koppar(I) jodid (CuI(3-pic), CuI(4-pic), CuI(3,4-lut) och (CuI(3,5-lut)). Den experimentella undersökningen delades in i olika delar. Först, syntesen och karakteriseringen av föreningarna både som pulver och som tunn film. Sedan studerades fotoluminiscensen av respektive förening. Därefter genomförde en ligand-utbytes-reaktion genom förgasning och slutligen bestämde livstiden av föreningarnas exciterade tillstånd.  Alla koppar(I) jodid föreningar som studerade gav upphov till emission både som pulver och som tunn film. Syntesen av tetranukleära kluster i pulverform resulterade i både kluster och polymer struktur. pXRD av pulvren CuI(3-pic), CuI(4-pic) och CuI(3,5-lut) bekräftade dess struktur som polymera strukturer. Däremot visade CuI(3-pic) termokromism. Strukturen för CuI (3,4-lut) kunde inte obekräftas. Den mest effektiva metoden för syntes av tunn film i det här fallet är med SILAR-metoden.  Fotoluminescensspektra för respektive tunn film skiljer sig från deras motsvarande pulverform och strukturen på tunn film är fortfarande outforskat. Emission av CuI(3-pic), CuI(4-pic) och CuI(3,4-lut) som tunn film var ungefär lika ~480 nm medan för CuI(3,5-lut) så var det på 518 nm. Med denna kontrast utfördes ligand-utbyte-reaktionen på tunn film av CuI(3-pic) med 3,5- lutidin.  Ligand-utbyte-reaktionen av CuI(3-pic) på tunn film via förgasning av 3,5-lutidin resulterar i en spektrumförskjutning från spektrumet av CuI(3-pic) till spektrumet av CuI(3,5-lut). Detta indikerar i en lyckad ligand-utbyte-reaktion.  Livslängderna för de undersökta föreningarna vilket har sin bästa passning i mono- exponentiell funktion var mellan 2,2 μs och 9,52 μs. Livstiderna bestämdes på de tunn film med ”time-resolved photoluminescence”. Ligand-utbyte-reaktionen observerades också med ”time- resolved photoluminescence” som avslöjar några stabila livstider under reaktionen vilket kan indikera bildning av intermedianer. De uppmätta livstiderna under ligand-utbyte-reaktionen har däremot sin bästa passning av bi-exponentiell funktion vilket kan bero på reaktionsförhållanden under mätningen och tunn filmernas homogenitet.

<p>The complexation reactions of silylenes (SiMe₂, SiPh₂ and SiMes₂) and germylenes (GeMe₂, GePh₂ and GeMes₂) with a series of O-, S-, N- and P-donors have been studied in hexanes solution. The equilibrium constants for complexation of SiMes₂ and GeMes₂ with 7 Lewis bases were determined, and demonstrate that the silylene is more Lewis acidic than the germylene by ca. 1 kcal mol^-1. Diethyl ether reacted with the six tetrellylenes with equilibrium constants that decrease in the order SiPh₂ > SiMe₂ > GePh₂ > GeMe₂ > SiMes₂ > GeMes₂, establishing a trend in the Lewis acidities of the silylenes and germylenes. Experimental results are complemented by calculated (G4) binding enthalpies of the MMe₂-donor complexes, which were found to correlate with Drago’s E and C parameters leading to the classification of SiMe₂ and GeMe₂ as borderline soft Lewis acids.</p> <p>A number of sigma-bond insertion reactions by transient silylenes was examined, namely the O-H, N-H and Si-O insertion reactions with alcohols, amines and siloxanes, respectively. In all cases the reactions were found to proceed via a two step mechanism in which the first step is a reversible formation of a Lewis acid-base complex. The second step was found to be a catalytic H-migration in the reactions with alcohols and amines; the catalysis by the alcohol is at least 10⁴ times faster than that by the amine. Complexes of silylenes with alkoxysilanes and siloxanes transform into the final products via a unimolecular [1,2]-silyl migration.</p> <p>Chalcogen abstraction reactions by silylenes (SiMe₂, SiPh₂, SiTmp₂ and SiMes₂) and germylenes (GeMe₂ and GePh₂) from oxiranes (cyclohexene oxide (CHO) and propylene oxide (PrO)) and thiiranes (cyclohexene sulfide (CHS) and propylene sulfide (PrS)) were investigated by laser flash photolysis and steady-state photolysis methods. The results indicate that the reaction proceeds via a two step mechanism, in which the first step is a reversible complexation followed by a unimolecular decomposition of the complex to yield products of chalcogen abstraction, namely alkenes and the corresponding R₂M=X transients (R = Me, Ph, Tmp and Mes, M = Si or Ge, X = O or S). Diphenylsilanethione was directly detected and identified on the basis of its spectra and reactivity with amines and alcohols. The O- and S- abstraction by silylenes proceed with ca. 50% efficiency; in contrast, no evidence for O-abstraction by GeMe₂ from CHO could be found, while propene was formed in ca. 35% yield in the reaction of GeMe₂ with PrS.</p> / Doctor of Philosophy (PhD)

Development of therapeutics is an extensive process, consuming significant amounts of time and requiring herculean synthetic efforts. A new therapeutic is most often designed from a previously commercialized scaffold, to increase the chance of success. Designing new molecular scaffolds can be extremely high risk and time consuming, yet at the same time the reward can be substantial. Accessing new molecular scaffolds, with efficient and “green” methods, is important in modern medicinal chemistry to diversify chemical space for therapeutic targets. There may be significant quantities of therapeutic candidates that have been over-looked due to synthetic challenges. There is a need for methodologies to synthesize challenging molecular scaffolds that are underexplored in commercialized therapeutics. The work described herein employs two distinct methodologies to access complex molecular scaffolds: 1) by developing a titanium (II) mediated Kulinkovich de-Meijere reaction arrested by Bredt’s rule and a suitable aryl sulfonyl moiety to afford diverse molecular scaffolds with potential for medicinal chemistry applications and 2) utilizing a [4 + 4] photocycloaddition of 2-pyridone-enolynes to access functionally rich cyclooctanoids that are capable of further photochemical transformations into even more complex molecular scaffolds. The titanium (II) mediated Kulinkovich reaction traditionally yields cyclopropylamines and cyclopropanols from amides and esters, respectively. The reaction involves two consecutive carbon-carbon bond forming steps. The bridged tricyclic intermediates would violate Bredt’s Rule and prevent the final carbon-carbon bond formation. This transformation can access a wealth of cyclic amino-ketones from olefin-tethered lactams. In addition, appropriate selection of an electron withdrawing group on nitrogen achieves the same bond sequestration. Interception of the titanafuran intermediate allows for electrophilic trapping of the titanium-carbon bond. The electronically arrested second carbon-carbon bond forming step adds generality to the interrupted Kulinkovich de-Meijere reaction to access the challenging molecular scaffolds of trans-α,α’-disubstituted cyclic ketones. Intramolecular [4 + 4] photoreaction of 2-pyridones with silyl 3-enol-1-ynes yields a highly reactive 1,2,5-cyclooctatriene. In the presence of a silanol proton source the allene is converted into a 1,3-diene. Without the combination of silyl 3-enol-1-ynes and silanol, as previously reported with 1,3-enynes, complex mixture of products is observed. Use of more nucleophilic solvents results in near quantitative yield of the cyclooctadienone through loss of silicon. Further photochemical manipulations of the cyclooctanoids allows for rapid scaffold diversification into bullvalene-like structures through a di-π-methane rearrangement. / Chemistry

Screening small molecule libraries is a powerful method for identifying biologically active substances. Current compound libraries are typically comprised of a large number of structurally similar compounds designed around bioactive core structures of known molecules. While the number of tested compounds are increasing, there has been a decline in drug-discovery success due to only a small region of chemical space being represented in these compound libraries. In addition, newly discovered biological targets tend not to be modulated by currently known natural products and molecular scaffolds. Diversity-oriented synthesis (DOS) aims to construct structurally novel and diverse products in a highly efficient manner to generate small-molecule libraries with a high degree of structural diversity and function. There is a need for new organic methodologies to access these atypical molecular scaffolds. The work presented here utilizes photochemical and titanium-mediated methodologies to access novel molecular scaffolds in two distinct directions: 1) by utilizing [2+2] photocycloaddition of pyridone-enynes to access functionalized cyclobutanoids capable of further modification and 2) by developing a novel Bredt’s rule-arrest Kulinkovich-de Meijere reaction to produce alkaloid building blocks with useful functionality. 2-Pyridones are known to undergo photo-initiated [2+2] and [4+4] cycloadditions with themselves and other conjugated -systems. These transformations provide rapid access to highly functionalized cyclobutanoid and cyclooctanoid derivatives capable of further manipulation to access both known and novel chemical space. Utilizing [2+2] photocycloaddition of pyridones conjugated with enyne partners we prepared polycyclic cyclobutanoids with excellent regio- and stereoselectivity. Further, these products were functionalized to give complex tetracyclic molecular scaffolds. The described approach to the 5-8-5 framework of the fusicoccane family features a key intramolecular [4+4] photocycloaddition of tethered pyridones. Intelligent design of the tether and proper choice of solvent affords rapid assembly of the polycyclic framework and sets the relative stereochemistry of five stereogenic centers. The strategy for construction of cyclooctanoid natural products is part of a long standing program to utilize the powerful photochemical properties of 2 pyridone. A novel approach for rapid access to a structurally diverse array of amino-ketone scaffolds employing a Kulinkovich-de Meijere reaction of inexpensive lactam-olefin building blocks has been developed. The formation of cyclopropylamines from alkenes and amides, the Kulinkovich-de Meijere reaction, involves two carbon-carbon bond-forming steps. Strategic use of a tricyclic intermediate can arrest the process if the second step requires formation of a bridgehead double bond. This intramolecular transformation results in formation of carbocyclic amino ketone building blocks. Further manipulation provides access to novel three-dimensional chemical space from these building blocks to produce a spectrum of fused bicyclic scaffolds in a divergent yet predictable manner. These products allow access to complex molecular space that can serve as a platform for medicinal and biochemical investigations. / Chemistry

There is a profound need for new antibiotics which overcome bacterial resistance. The predominant source for these is natural products; however, they are often quickly rendered ineffective due to antibiotic resistance. A proven method in drug discovery is improving the properties of natural products through diverted total synthesis (DTS). Of particular interest is promysalin, which is produced by Pseudomonas putida, and selectively inhibits the growth of Gram-negative pathogenic bacteria Pseudomonas aeruginosa at nanomolar concentrations. The work herein describes modifications to the side chain which were shown to modulate antibacterial potency and specificity. A similarly inspired approach to countering antibiotic resistance is the targeted modification of a single carbon to silicon, motivated by the proven success of this substitution shown in pharmaceuticals and amino acids. The target for this modification is albocycline, a known macrolactone antibiotic that exhibits potent antibiotic activity against S. aureus. Replacing the C4 carbon of albocycline with silicon will provide sila-albocycline with enhanced hydrogen bonding properties and altered lipophilicity due to the slight changes from the carbon to silicon atom. In addition, there is anticipated intrinsic stability of the silanol toward rearrangement reactions than carbon-based. The proposed synthesis diverts from the known total synthesis of albocycline, as reported by the Andrade Group. This work details the efforts made towards the total synthesis of sila-albocycline. Lastly, there is untapped potential for UV-promoted photochemistry to create molecular scaffolds, which may lead to novel synthetic routes to complex molecules in addition to providing new polycycles that may expand current medicinal products. The work herein describes the synthesis of tethered chloro- and methoxy-substituted benzyl alcohols to 2-pyridones and the resulting products when exposing the solution to ultraviolet light. This generated new polycycles with complex structures which have unexplored biological or medicinal properties. / Chemistry

Characterization of a material’s surface, structural and physical properties is essential to understand its chemical reactivity. Control over these properties helps tailor a material to a particular application of interest. The research presented in this dissertation focuses on characterizing a synthetic method for carbon nanomaterials and the determination of structural properties of manganese oxides that contribute to its reactivity for environmental chemistry. In particular, one research effort was focused on the tuning of synthetic parameters towards the formation of carbon nanomaterials from gaseous methane and gaseous mixtures containing various mixtures of methane, argon and hydrogen. In a second research effort, photochemical and water oxidation chemistry were performed on the manganese oxide, birnessite, to aid in the remediation of arsenic from the environment and provide more options for alternative energy catalysts, respectively. With regard to the synthesis of novel carbonaceous materials, the irradiation of gaseous methane with ultrashort pulse laser irradiation showed the production of carbon nanospheres. Products were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet (UV) Raman spectroscopy, and infrared spectroscopy. Increasing the pressure of methane from 6.7 to 133.3 kPa showed an increase in the median diameter of the spheres from ~500 nm to 85 nm. Particles with non-spherical morphologies were observed by TEM at pressures of 101.3 kPa and higher. UV Raman spectroscopy revealed that the nanospheres were composed of sp2 and sp3 hybridized carbon atoms, based on the presence of the carbon D and T peaks. A 30% hydrogen content was determined from the red shift of the G peak and the presence of a high fluorescence background. Upon extending this work to mixtures of methane, argon, and hydrogen it was found that carbon nanomaterials with varying composition and morphology could be obtained. Upon mixing methane with other gases, the yield significantly dropped, causing flow conditions to be investigated as a method to increase product yield. Raman spectra of the product resulting from the irradiation of methane and argon indicated that increasing the argon content above 97% produced nanomaterial composed of hydrogenated amorphous carbon. In a second research effort, the effect of simulated solar radiation on the oxidation of arsenite [As(III)] to arsenate [As(V)] on the layered manganese oxide, birnessite, was investigated. Experiments were conducted where birnessite suspensions, under both anoxic and oxic conditions, were irradiated with simulated solar radiation in the presence of As(III) at pH 5, 7, and 9. The oxidation of As(III) in the presence of birnessite under simulated solar light irradiation occurred at a rate that was faster than in the absence of light at pH 5. At pH 7 and 9, As(V) production was significantly less than at pH 5 and the amount of As(V) production for a given reaction time was the same under dark and light conditions. The first order rate constant (kobs) for As(III) oxidation in the presence of light and in the dark at pH 5 were determined to be 0.07 and 0.04 h−1 , respectively. The As(V) product was released into solution along with Mn(II), with the latter product resulting from the reduction of Mn(IV) and/or Mn(III) during the As(III) oxidation process. Experimental results also showed no evidence that reactive oxygen species played a role in the As(III) oxidation process. Further research on the triclinic form of birnessite focused on its activation for water oxidation. Experiments were performed by converting triclinic birnessite to hexagonal birnessite in pH 3, 5, and 7 DI water with stirring for 18 hrs. Once the conversion was complete, the solid samples were characterized with TEM and x-ray photoelectron spectroscopy (XPS). The resulting hexagonal birnessites from experiment at pH 3, 5, and 7 possessed the same particle morphology and average surface oxidation states within 1% of each other. This observation supported the claim that upon transformation, Mn(III) within the sheet of triclinic birnessite migrated into the interlayer region of the resulting hexagonal birnessite. Furthermore, the migration of Mn(III) into the interlayer and formation of the hexagonal birnessite led to an increased chemical reactivity for water oxidation compared to the bulk. Electrochemical studies showed that the overpotential for water oxidation associated with the pH 3, 5, and 7 samples was 490, 510, and 570 mV, respectively. In another set of experiments, ceric ammonium nitrate was used to test birnessite for water oxidation reactivity. These experiments showed that the pH 3 birnessite produced the most O2 of all the samples, 8.5 mmol O2/mol Mn, which was ~6 times more than hexagonal birnessite which did not undergo post-synthesis exposure to low pH conditions. / Chemistry

The work reported in this thesis involves the synthesis of a series of monometallic and polymetallic complexes incorporating the tridentate polypyridyl bridging ligand tpp (where tpp = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) and an investigation of their ground and excited state properties. A series of ruthenium monometallic chromophore complexes has been prepared varying the ligands coordinated on the metal center. The systematic alteration of the ligands has enhanced the understanding of the electrochemical and spectroscopic properties of ruthenium polypyridyl tridentate complexes. In contrast to [Ru(tpy)₂]²⁺ (where tpy = 2,2’:6’,2’’-terpyridine), these monometallic complexes and many of the polymetallic systems emit in solution at room temperature. Methylation of one of the remote pyridine nitrogens on tpp has been accomplished forming a covalently coupled viologen that can potentially function as an electron acceptor. Two classes of synthetically useful bimetallic complexes of the form [(tpy)M(tpp)RuCl₃]⁺ and [(tpy)M(tpp)Ru(tpp)]⁴⁺ have been prepared (where M = Ru(II) or Os(II)). Synthetic methods have been developed for the stepwise construction of tpp bridged systems by a building block approach. In all bimetallic complexes, the tpp bridging ligand is the site of localization of the LUMO. In the [(tpy)M(tpp)RuCl₃]⁺ systems, the ruthenium metal coordinated to tpp and three chlorides is the easiest to oxidize and is the site of localization of the HOMO. In contrast, for the [(tpy)M(tpp)Ru(tpp)]⁴⁺ systems, the HOMO is localized on the metal being varied, either Ru or Os. This gives rise to complexes which possess a lowest lying excited state that is always a MLCT state involving tpp but can be tuned to involve Ru or Os metal centers. Bimetallic systems that incorporate this tpp ligand have long lived excited states in solution at room temperature (t >100 ns). The bimetallic complex [(tpy)Ru(tpp)IrCl₃]²⁺ has been studied and shown to be an electrocatalyst for the reduction of CO₂ to CO and formate. The synthesis of the monometallic complexes has advanced the understanding of the ground and excited state properties of tridentate compounds. Incorporation of these complexes into bimetallic systems has aided in the understanding of the perturbations of these properties that occur upon formation of a polymetallic system. / Ph. D.