| Summary: | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008. === This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. === Vita. === Includes bibliographical references. === The design, synthesis and characterization of organic electronic materials, in particular luminescent conjugated polymers, with structural motifs that allow for the controlled modulation of their photophysical properties are presented. In Chapter 1, the synthesis of new heterocyclic oligo(phenylene) analogues based on soluble, nonaggregating 1,2-diazines is reported. Palladium-catalyzed reductive coupling methods were developed to allow for the preparation of large quantities of iptycene-derived bipyridazines and biphthalazines, and the controlled synthesis of well-defined oligomers up to sexipyridazine. Crystallographic, spectroscopic and computational evidence indicate that in these analogues, hindrance at the ortho position is relaxed relative to poly(phenylene)s, which can favor planarization and extension of conjugation. New poly(aryl ether)s that incorporate iptycene-derived pyridazines have been prepared by three different synthetic routes, including a novel reductive polymerization of poly(aryl alkyl ether)s (Chapter 2). Some of these polymers exhibit low dielectric constants due to the introduction of internal free volume. Iptycene-derived pyridazines were also incorporated in conjugated organic materials that show thermotropic liquid crystalline properties and in platinum-based monomers for conjugated phosphorescent polymers that exhibit high luminescence efficiency under ambient conditions (Chapter 3). The luminescent properties of these platinum complexes are attributed to the introduction of steric bulk that prevents the formation of quenched aggregates. The donor-acceptor strategy to bandgap engineering was applied to the preparation of a highly selective fluorescent probe for thiol bioimaging (Chapter 4), and to the synthesis of conjugated luminescent polymers that incorporate new electron deficient monomers based on 2,1,3-benzothiadiazole and 2,1,3-benzooxazole bearing solubilizing side-chains (Chapter 5). === (cont) The exquisite control over conformation and surface density offered in Langmuir monolayers of amphiphilic poly(phenylene ethynylene)s at the air-water interface was exploited in spectroscopic studies of energy transfer to perylene monoimide end-groups (Chapter 6). In these, planarization increases the efficiency of intramolecular energy transfer at low surface densities, and intermolecular energy transfer pathways become predominant at high surface densities. The modulation of energy transfer at dipolar interfaces provides a transduction mechanism that makes these polymers attractive platforms for the development of new biosensors for surface interactions. === by Jean Bouffard. === Ph.D.
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