Structural analysis of J-aggregating molecules by absorption, Raman, and NMR spectroscopies.
Item
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Title
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Structural analysis of J-aggregating molecules by absorption, Raman, and NMR spectroscopies.
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Identifier
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AAI3310760
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identifier
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3310760
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Creator
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Mercier, Philippe Heli.
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Contributor
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Adviser: Daniel L. Akins
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Date
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2008
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Physical
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Abstract
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Structural properties of J-aggregating molecules were studied using absorption, Raman and NMR spectroscopies. Results for PIC and 2,2'-carbocyanine showed that although the molecules were similar structurally, their NMR spectra showed fundamental differences in the bonding character of the bonds connecting the moieties in both molecules, these differences affected their conjugation, and also had consequences in the molecules' Raman spectra. TTBC and TDBC-4 were also studied and it was shown through absorption studies that in silver colloidal formulations, J-aggregates of TTBC formed preferentially on the silver nanoparticles rather than in solution. Similarities between Raman spectra of aggregated TTBC in colloidal silver and on silver electrode supported that conclusion and suggested that the optical coherence length of the J-aggregate was sufficiently short as to not be affected by the curvature of the nanoparticle. Structural isomers were found to exist in solutions of both TTBC and TDBC-4 indicating the greater pi bond character of the bonds in the polymethine chain compared to those of 2,2'-carbocyanine. A simple model arguing for both an optical and orbital coupling of adjacent molecules in order to obtain all the special characteristics of J-aggregates was presented and was used to discuss intrinsic limitations to the coherence length that were unrelated to structural defects. This model was also used to explain the occurrence of disordered aggregates and other similar structures as well. Based on the concepts proposed, it was possible to develop a systematic method to elucidate a credible structure for the TSPP J-aggregate that agreed with conclusions advanced in the literature. Cyclic voltammetry was conducted on two metal porphyrins, Fe-TSPP and Co-protoporphyrin with the intent to use their aggregating properties to synthesize uniform-sized metal nanoparticles. Although the cyclic voltammograms did not show that the porphyrins released the metal ions from their core, it was determined that such a process could still occur and that further study with other metal porphyrins was needed. The combined data from Raman and NMR methods provided the necessary information on conjugation and conformational differences between similar molecules to make determinations that had not been previously possible with either method individually.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
