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π-Conjugated organic materials have gained much attention and proven useful in multiple optoelectronic applications such as nonlinear optics, organic light-emitting diodes, organic solar cells, and organic field-effect transistors due to their low cost, facile synthesis, light weight, fine tunability, high processibility and mechanical flexibility. Particularly, molecular designs of π-conjugated systems featuring electron donors and acceptors (donor-acceptor systems), or just electron-deficient moieties (acceptor materials) are essential and valuable in realizing critical properties that are desirable for a wide range of optoelectronic materials, such as nonlinear optical materials, thermally activated delayed fluorescence emitters, solar harvesting materials and organic n-type semiconductors. Pentafluorosulfanyl (SF5) is a strong electron-withdrawing group that can certainly be applied in the structural designs of donor-acceptor systems and acceptor materials. Along with its strongly electron-withdrawing nature, SF5 is also sterically bulky, chemically/thermally robust and hydrophobic/lipophilic, rendering it unique among electron-withdrawing groups and highly desirable in various optoelectronic materials. However, the SF5 group was only adopted sporadically in a small number of optoelectronic materials and its potential in a wide range of other optoelectronic materials remained largely untapped. Therefore, this thesis aims to investigate the potential of SF5 in a wider variety of molecular designs for novel optoelectronic materials. Specifically, Chapter One provides a brief overview of optoelectronic materials and covers the potential and reported application of SF5 in the molecular designs for different optoelectronic organic materials. Chapter Two will discuss the synthesis of five SF5-containing push-pull dyes and their photophysical properties, particularly their large two-photon absorption characters. In Chapter Three, two styrenic polymers bearing the polar SF5 groups are synthesized and utilized as charge-storage electrets in nonvolatile organic field-effect transistor memory devices. Also, their superior memory device performance to other polar styrenic polymers will be revealed. Chapter Four elaborates the synthesis of a series of SF5-functionalized ullazine derivatives, with the success of synthesis ascribed to the chemical and thermal robustness of SF5. Additionally, the photophysical and electrochemical properties of these SF5-functionalized ullazine derivatives will be investigated, and their potential application in dye-sensitized solar cells will be examined. Finally, in Chapter Five, the work presented in Chapters Two through Four, as well as the previously reported work on SF5-containing optoelectronic materials (in Chapter One), is summarized. In addition, the future scope of SF5 in optoelectronic materials will be proposed as well.

Si nanoparticles are new prospective optoelectronic materials. Unlike bulk Si cry-stals, Si nanoparticles display intriguing room-temperature photoluminescence. A major challenge in the fabrication of Si nanoparticles is the control of their size distribution. The rare-earth element Er has unique photo emission properties, including low pumping power, and a temperature independent, sharp spectrum. The emission wavelength matches the transmission window of optical fibers used in the telecommunications industry. Therefore, the study of Er-doped Si nanoparticles may have practical significance. The goals of the research described in this dissertation are to investigate vapor phase pyrolysis methods and to characterize the microstructure and associated defects, particles size distributions and photoluminescence efficiencies of doped and undoped Si nanoparticles using analytical transmission electron microscopy, high resolution electron microscopy, and optical spectroscopy. Er-doped and undoped Si nanoparticles were synthesized via vapor-phase pyrolysis of disilane at Texas Christian University. To achieve monodisperse size distributions, a process with fast nucleation and slow growth was employed. Disilane was diluted to 0.48% with helium. A horizontal pyrolysis oven was maintained at a temperature of 1000 °C. The oven length was varied from 1.5 cm to 6.0 cm to investigate the influence of oven length on the properties of the nanoparticles. The Si nanoparticles were collected in ethylene-glycol. The doped and undoped Si nanoparticles have a Si diamond cubic crystal structure. Neither Er precipitation, Er oxides or Er silicides were detected in any of the samples. The Er dopant concentration was about 2 atom% for doped samples from the 3.0 and 6.0 cm ovens as determined by quantitative analysis using X-ray energy dispersive spectroscopy. The average Si nanoparticle size increases from 11.3 to 15.2 nm in the doped samples and from 11.1 to 15.7 nm in the undoped samples as the oven length increases from 1.5 to 6.0 cm. HREM data show that average Si nanocrystallite size varies from 6.4 to 3.3 to 5.9 nm in the doped samples, and from 7.5 to 12.2 nm in the undoped samples as the oven length increases. Room-temperature Er photoluminescence has been detected near 1.54 :m from all doped samples. Saturation of the Er photoluminescence intensity at large emission power and the monotonic decrease of the intensity as a function of the emission wavelength in the doped sample from the 3.0 cm oven suggest that a carrier-mediated energy transfer process occurs in the Er-doped Si nanoparticles. It is the first time to successfully fabricate and investigate Er-doped Si nanoparticles.

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