Jeanne E. Pemberton

Regents Professor

Research

I. The Chemistry of Organic Semiconductors and their Interfaces in Molecular Electronic & Photonic Devices

The interfacial regions between phases are sites of critical importance in many relevant processes and technologies. Despite decades of intense study, our understanding of the chemistry of interfacial and surface processes at the molecular level is still only modestly developed. Thus, the development of adequate tools with which to study surface and interfacial chemistry and elucidation of the molecular details of such complex chemistry represent two of the most exciting frontiers of modern measurement science. Our research seeks to develop an understanding of such chemistry in several technologically important areas including organic semiconductor-based devices. Methodologies employed for these efforts include surface vibrational spectroscopies, electrochemistry, surface electron spectroscopies, work function measurements, ellipsometry, fluorescence microscopy, electron microscopy, and the scanning probe microscopies (AFM and STM). These methods are supplemented by more conventional chemical measurement tools (e.g. mass spectrometry, NMR spectroscopy, FTIR spectroscopy, fluorescence spectroscopy) as needed for complete characterization of relevant solution and interfacial systems.

Solid-state organic semiconductor (OSC) materials are the essential active components of a variety of existing and emerging technologies, including LED lasers and organic-based electronic and photonic devices. These technologies suffer from limited lifetimes due to the inevitable degradation of OSCs through poorly defined chemical, photochemical and photophysical processes, especially in operando, or under conditions of operation. Addressing these limitations requires characterization of the molecular structural, electronic, and charge transport attributes of these OSC materials during and after degradation.  We are employing a suite of state-of-the-art methods to study OSCs in environments that systematically increase in chemical and optoelectronic complexity, including in operando. Tools being used include surface vibrational spectroscopies (Raman, PM-IRRAS) in environments ranging from ambient to ultrahigh vacuum, synchrotron IR nanospectroscopy (SINS), and x-ray photoelectron spectroscopy (XPS). Exceptional among these tools are our capabilities for UHV Raman spectroscopy for detailed chemical characterization, which are being implemented in operando.  Specific objectives being addressed through this work include: 1) Intrinsic OSC chemistry: What roles do intrinsic chemical nature, degree and type of crystallinity, and frontier orbital energetics of the OSC play in dictating chemical, photochemical, and photophysical degradation of the OSC? How do different chemical penetrants contribute to or drive these degradation pathways as a function of time and exposure? What role do thermal versus photolytic pathways play in OSC degradation? 2) Effects of "intrinsic" catalysts and materials interfaces: What roles do catalyst species, introduced as impurities during the fabrication process, created through unintended chemical reactions during the fabrication process, or created through degradation reactions, play in initiating or accelerating degradation pathways? What role do contacts of the OSC with transparent conductive oxide or metallic electrodes play in initiating or accelerating degradation pathways? 3) In operando effects:  What role does the presence of an applied electric field play in promoting or altering the chemical, photochemical, or photophysical degradation pathways elucidated above in Objectives 1 and 2, or in changing their mechanisms? What role does the presence of excess charge carriers near OSC-electrode contacts and interfaces with other active materials play in promoting or altering the chemical, photochemical, or photophysical degradation pathways elucidated above?

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New Functional Materials from Sugar-based Glycolipids: Glyonic Liquids

Glycolipids are surfactants based on sugars with variable lipid tails. Surfactants are critical, ubiquitous chemicals in many consumer products areas, technologies, and industrial processes. The ubiquity of surfactants as essential chemicals and their massive industrial use, coupled with emerging concerns about their long-term environmental impacts, present a compelling opportunity for advances in molecular design and synthesis of green surfactants. Widespread interest in these issues supports exploration of all viable alternatives to meet the increasing demands of the global surfactant market, predicted to reach $40B annually by 2018. This work grew out of concerns about the toxicity of many conventional synthetic surfactants as well as their persistence in the environment that is driving regulatory and consumer pressure to develop greener and more sustainable alternatives to these materials. Building on a collaborative effort to explore the systematic design, synthesis, and characterization of a wide array of new glycolipid surfactants, we have identified new functional sugar-based materials that are being explored for different applications. We have made ionic liquids, liquids containing only ionic species, from sugar-based surfactants that we have termed glyonic liquids. These materials demonstrate superionic proton conductivity and thus, may be of interest for electrochemical device applications.