2026-09-23T16:37:29Zhttps://dspace.mit.edu/server/oai/request

oai:dspace.mit.edu:1721.1/80462022-01-13T07:54:21Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022

Timothy M. Swager. Tovar, John Dayton, 1975- Massachusetts Institute of Technology. Dept. of Chemistry. Massachusetts Institute of Technology. Department of Chemistry 2005-08-24T19:54:34Z 2005-08-24T19:54:34Z 2002 2002 http://hdl.handle.net/1721.1/8046 51006907 Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2002. Vita. Includes bibliographical references. This dissertation examines the synthesis of electronically diverse polycyclic aromatics within discrete molecular regimes and as incorporated into robust conjugated polymers. We have pursued two strategies for obtaining these large aromatics from rather elaborate yet readily available pendant aromatic precursors: electrophilic and oxidative cyclizations. Chapters One and Two describe research directed towards expansion of electrophilic cyclizations that utilize alkyne functionality to construct aromatized systems. Strongly-acidic conditions provide transient cationic intermediates that participate in annulations with adjacent arenes or amides to yield dibenzanthracenes or dioxanthracenes, respectively. In the latter case (Chapter Two), smaller model compounds confirmed this unique reactivity and helped to establish synthetic routes that yield isoquinolines in one synthetic step from aryl carbonyls appended with ortho-substituted alkynes. Chapters Three and Four describe efforts directed towards thiophene-based polycyclic aromatics. Tandem cyclization-polymerizations of pendant thiophenes provide robust electrochromic materials with readily tuneable optical bandgaps. Arenes placed adjacent to the highly-reactive oxidized thienyl moieties force this unique reactivity by biasing the system toward intramolecular cyclization. Chemical and electrochemical studies of related model systems further established the tandem reactivity. The generality of this controlled oxidative cyclization provided several readily-functionalized sulfur-based polycyclics. Using this chemistry, larger molecular and polymeric structures with tailored functionality may allow for a survey of electronic applications such as plastic organic field-effect transistors. (cont.) After employing the new routes to large polycyclic aromatics, these scaffolds helped to study the optimization of exciton migration and the mechanical tuneability of polymer chromicity. The thiophene-based platforms allowed for an assessment of the photophysical effects of chromophore aromatization within conjugated arylene-ethynylene polymers. As detailed in Chapter Four, the incorporation of planar and aromatized moieties greatly reduces the rate of fluorescence decay relative to closely-related yet non-aromatized structures. These easily-functionalized substrates also led to an examination of a new type of mechanochromism as introduced in Chapter Five. Conformational alterations within the polymer could lead to attenuated excimer-like behavior, and the synthetic schemes presented allow for the incorporation of a variety of discrete chromophores that may provide clean and sharp optical properties when compared to conformationally-disordered conjugated polymers. by John Dayton Tovar. Ph.D. 328 leaves 18207767 bytes 18207525 bytes application/pdf application/pdf eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Chemistry. Synthesis and utility of electronically diverse polycyclic aromatics Thesis application/pdf false Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="16db1148-94a4-4752-974c-bf627ad1021e"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Synthesis and utility of electronically diverse polycyclic aromatics</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2002</PublicationDate> <Authors> <Author> <DisplayName>Tovar, John Dayton, 1975-</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Chemistry.</Keyword> <Abstract>This dissertation examines the synthesis of electronically diverse polycyclic aromatics within discrete molecular regimes and as incorporated into robust conjugated polymers. We have pursued two strategies for obtaining these large aromatics from rather elaborate yet readily available pendant aromatic precursors: electrophilic and oxidative cyclizations. Chapters One and Two describe research directed towards expansion of electrophilic cyclizations that utilize alkyne functionality to construct aromatized systems. Strongly-acidic conditions provide transient cationic intermediates that participate in annulations with adjacent arenes or amides to yield dibenzanthracenes or dioxanthracenes, respectively. In the latter case (Chapter Two), smaller model compounds confirmed this unique reactivity and helped to establish synthetic routes that yield isoquinolines in one synthetic step from aryl carbonyls appended with ortho-substituted alkynes. Chapters Three and Four describe efforts directed towards thiophene-based polycyclic aromatics. Tandem cyclization-polymerizations of pendant thiophenes provide robust electrochromic materials with readily tuneable optical bandgaps. Arenes placed adjacent to the highly-reactive oxidized thienyl moieties force this unique reactivity by biasing the system toward intramolecular cyclization. Chemical and electrochemical studies of related model systems further established the tandem reactivity. The generality of this controlled oxidative cyclization provided several readily-functionalized sulfur-based polycyclics. Using this chemistry, larger molecular and polymeric structures with tailored functionality may allow for a survey of electronic applications such as plastic organic field-effect transistors.</Abstract> <Abstract>(cont.) After employing the new routes to large polycyclic aromatics, these scaffolds helped to study the optimization of exciton migration and the mechanical tuneability of polymer chromicity. The thiophene-based platforms allowed for an assessment of the photophysical effects of chromophore aromatization within conjugated arylene-ethynylene polymers. As detailed in Chapter Four, the incorporation of planar and aromatized moieties greatly reduces the rate of fluorescence decay relative to closely-related yet non-aromatized structures. These easily-functionalized substrates also led to an examination of a new type of mechanochromism as introduced in Chapter Five. Conformational alterations within the polymer could lead to attenuated excimer-like behavior, and the synthetic schemes presented allow for the incorporation of a variety of discrete chromophores that may provide clean and sharp optical properties when compared to conformationally-disordered conjugated polymers.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>