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Design, Synthesis and Study of Supramolecular Donor – Acceptor Systems Mimicking Natural Photosynthesis Processes

Description: This dissertation investigates the chemical ingenuity into the development of various photoactive supramolecular donor – acceptor systems to produce clean and carbon free energy for the next generation. The process is inspired by the principles learned from nature’s approach where the solar energy is converted into the chemical energy through the natural photosynthesis process. Owing to the importance and complexity of natural photosynthesis process, we have designed ideal donor-acceptor systems to investigate their light energy harvesting properties. This process involves two major steps: the first step is the absorption of light energy by antenna or donor systems to promote them to an excited electronic state. The second step involves, the transfer of excitation energy to the reaction center, which triggers an electron transfer process within the system. Based on this principle, the research is focused into the development of artificial photosynthesis systems to investigate dynamics of photo induced energy and electron transfer events. The derivatives of Porphyrins, Phthalocyanines, BODIPY, and SubPhthalocyanines etc have been widely used as the primary building blocks for designing photoactive and electroactive ensembles in this area because of their excellent and unique photophysical and photochemical properties. Meanwhile, the fullerene, mainly its readily available version C60 is typicaly used as an electron acceptor component because of its unique redox potential, symmetrical shape and low reorganization energy appropriate for improved charge separation behavior. The primary research motivation of the study is to achieve fast charge separation and slow charge recombination of the system by stabilizing the radical ion pairs which are formed from photo excitation, for maximum utility of solar energy. Besides Fullerene C60, this dissertation has also investigated the potential application of carbon nanomaterials (Carbon nanotubes and graphene) as primary building blocks for the study of the artificial photosynthesis process.
Date: December 2015
Creator: KC, Chandra Bikram

Studies of spin alignment in ferrocenylsilane compounds and in regiospecific oxidation reactions of 1,9-dimethylpentacyclo [,6.03,10.05,9]undecane-8,11-dione.

Description: Part I. The syntheses of a series of stable ferrocenylsilane compounds and their corresponding polyradical cations are reported. Electron spin properties of these molecules were investigated by cyclic voltammetry, ESR, and magnetic susceptibility measurements. All the compounds presented, showed significant electronic communication (>100 mV) between the redox centers by CV. Part II. Baeyer-Villiger oxidation of (1,9-dimethyl-PCU-8,11-dione) was performed using m-chloroperoxybenzoic acid in 1:2 molar ratios. The product obtained was the corresponding dilactone 113. The structure of the reaction products was established unequivocally via single crystal X-ray diffraction methods. The reaction of the 1,9-dimethyl-PCU-8,11-dione with 1:1 molar ratio of m-chloroperoxybenzoic acid produced again the dilactone 113, and not the expected monolactone 114. Ceric ammonium nitrate (CAN) promoted oxidation reaction of 1,9-dimethyl-PCU-8,11-dione afforded a mixture of dimethylated lactones, which indicated unique reaction mechanism pathways. These individual isomers, 115 and 116, have been isolated from these mixtures via column chromatography by using silica gel as adsorbent followed by fractional recrystallization of individual chromatography fractions. Structures of these pure products have been established unequivocally by application of single crystal X-ray crystallographic methods.
Date: August 2006
Creator: Atim, Silvia

Synthesis and characterization of quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers and reaction chemistry of the diphosphine ligand 2,3-bis(diphenylphosphino)-N-p-tolylmaleimide (bmi) at triosmium carbonyl clusters.

Description: Quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers have been synthesized as possible specific metal host systems. The synthesis and characterization of quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers have been described. The characterization of these host systems have been fully achieved in solution by using various techniques such as IR, 1H NMR, and 13C NMR spectroscopic methods, high-resolution mass spectrometry (HRMS), elemental microanalysis, and X-ray crystallographic analysis in case of one quinoxaline-functionalized, cage-annulated oxacrown ether compound. The synthesis of the diphosphine ligand 2,3-bis(diphenylphosphino)-N-p-tolylmaleimide (bmi) is described. The substitution of the MeCN ligands in the activated cluster 1,2-Os3(CO)10(MeCN)2 by the diphosphine ligand bmi proceeds rapidly at room temperature to furnish a mixture of bridging and chelating Os3(CO)10(bmi) isomers and the ortho-metalated product HOs3(CO)9[μ-(PPh2)C=C{PPh(C6H4)}C(O)N(tolyl-p)C(O)]. Thermolysis of the bridging isomer 1,2-Os3(CO)10(bmi) under mild conditions gives the chelating isomer 1,1-Os3(CO)10(bmi), whose molecular structure has been determined by X-ray crystallography. The kinetics for the ligand isomerization have been investigated by UV-vis and 1H NMR spectroscopy in toluene solution over the temperature range of 318-348 K. On the basis of kinetic data conducted in the presence of added CO and the Eyring activation parameters, a non-dissociative phosphine migration across one of the Os-Os bonds is proposed. Orthometalation of one of the phenyl groups associated with the bmi ligand is triggered by near-UV photolysis of the chelating cluster 1,1- Os3(CO)10(bmi).
Date: December 2006
Creator: Poola, Bhaskar

Synthesis and Complexation Studies of Novel Functionalized Crown Ethers and Azacrown Ethers

Description: Novel cage-functionalized azacrown ethers, i.e. 51, 52, 53, 55, 57, 61 and 62, which have various crown cavity and different number of nitrogen atoms incorporated, have been prepared. X-ray structures of 53, 55 and 57 have been obtained for the study of the crown topological structure. The complexation properties of crown 51, 52, 57, 61 and 62 have been evaluated via alkali metal picrate extraction, silver picrate extraction and ESI-MS study. The novel cage-fuctionalized azacrown ethers generally exhibit high avidity and selectivity towards Ag+ versus alkali metal ions and some transition metals i.e. Cu2+, Mn2+, Zn2+, Ni2+ and Pb2+. Crown 61 displays significant avidity and selectivity toward K+ in alkali metal picrate extraction experiments vis-à-vis the remaining alkali metal picrates. Three types of ditopic ion-exchange receptors for sodium hydroxide extraction study have been designed. All of the crown ether molecules have proper cavity for selective sodium complexation and have weakly acidic ionizable alcohols for sodium-proton exchange under strongly basic conditions. Crown 80 and 81 were synthesized; key intermediates for the synthesis of crown 82, 83 and 84 have been prepared. The preparation of 99 afforded an unexpected crown 103. The preparation of 109 had been attempted, but could not be successfully isolated. Four novel cage-functionalized calix[4]arene crown-5, i.e. 113-116, have been synthesized. The structures of 113 and 116 have been established by X-ray crystal structural analysis and NMR spectral analysis. The complexation properties of the four ionic receptors have been studied via alkali metal picrate extraction experiments. Crown 115 and 116 display more than modest avidity toward alkali metal ions and are most selective toward K+ vis-à-vis 113 and 114.
Date: May 2006
Creator: Huang, Zilin

Synthesis and Properties of Novel Cage-Annulated Crown Ethers

Description: Three cage-functionalized polyoxacrown ethers (9, 10 and 12) and four novel cage-functionalized polyoxamonoazacrown ethers (18, 20, 25 and 29) that contain 3,5-disubstituted-4-oxahexacyclo[,6.03,10.05,9.08,11]dodecane ("oxahexacyclic") moiety have been synthesized and their respective alkali metal picrate extraction profiles along with that of three analogues 13, 14 and 21 have been obtained. The observed avidities and selectivities of the host molecules toward complexation and transport of alkali metal picrates can be related to the size and shape of their respective macrocyclic cavity and the number of donor atoms. The effect of N-alkyl substitution on the complexation properties of azacrown ethers has been studied. The avidity of N-Et azacrown ethers toward complexation with alkali metal cations is generally higher than that of the corresponding non-N-alkylated hosts. However, the presence of an N-Et group appears to have a negligible effect upon their relative selectivities in their regards. The effect of pH on extraction process was studied; it was thereby determined that the alkali metal picrate extraction experiments are best performed at high pH (ca. 11-12).
Date: May 2003
Creator: Huang, Zilin