Physical Sciences and Mathematics Commons^™

Isolating The Electronic Effects Of Systematic Twist In Highly Substituted Aromatic Hydrocarbons Using Density Functional Theory, Grace Tully, Emily A. Jarvis

Honors Thesis

Density functional theory (DFT) was employed to investigate dodecaphenyltetracene as well as similar molecules containing differing backbone lengths and electron withdrawing groups with interest in manipulating the twist to lower the LUMO level for increased electron mobility. Optimization and frequency time-independent calculations followed by time-dependent (TD-DFT) energy calculations were performed at the B3LYP/G-311G level of theory to analyze electronic trends as a result of increased backbone length and consequently distorted end-to-end molecular twist. These calculations demonstrate a linear relationship with negative slope between the estimated HOMO-LUMO, fundamental, and optical gaps as a function of the number of fused rings along …

Synthesis And Characterization Of Unique Pyridazines, William Hobbs

Senior Honors Theses

The field of semiconductive organic chemistry is vast and expanding as numerous applications are being discovered for semiconductors. The research reported in this thesis focuses on the synthesis and characterization of three pyridazines. Pyridazines are organic heterocyclic aromatic semiconductors containing nitrogen and are planar in structure. The three pyridazine compounds were successfully isolated as evidenced by a high percent yield and then characterized by melting point and infrared spectroscopy. The research goal was achieved as a small library of pyridazines was compiled to be further analyzed concerning their potential within various applications in the electronic and industrial world.

Thermoelectric Transport In Disordered Organic And Inorganic Semiconductors, Meenakshi Upadhyaya

Doctoral Dissertations

The need for alternative energy sources has led to extensive research on optimizing the conversion efficiency of thermoelectric (TE) materials. TE efficiency is governed by figure-of-merit (ZT) and it has been an enormously challenging task to increase ZT > 1 despite decades of research due to the interdependence of material properties. Most doped inorganic semiconductors have a high electrical conductivity and moderate Seebeck coefficient, but ZT is still limited by their high lattice thermal conductivity. One approach to address this problem is to decrease thermal conductivity by means of alloying and nanostructuring, another is to consider materials with an inherently low …

Raising Dielectric Permittivity Mitigates Dopant-Induced Disorder In Conjugated Polymers, Meenakshi Upadhyaya, Michael Lu-Díaz, Subhayan Samanta, Muhammad Abdullah, Keith Dusoe, Kevin R. Kittilstved, Dhandapani Venkataraman, Zlatan Akšamija

Electrical and Computer Engineering Faculty Publication Series

Conjugated polymers need to be doped to increase charge carrier density and reach the electrical conductivity necessary for electronic and energy applications. While doping increases carrier density, Coulomb interactions between the dopant molecules and the localized carriers are poorly screened, causing broadening and a heavy tail in the electronic density-of-states (DOS). The authors examine the effects of dopant-induced disorder on two complimentary charge transport properties of semiconducting polymers, the Seebeck coefficient and electrical conductivity, and demonstrate a way to mitigate them. Their simulations, based on a modified Gaussian disorder model with Miller-Abrahams hopping rates, show that dopant-induced broadening of the …

Micro-Raman Imaging Of Isomeric Segregation In Small-Molecule Organic Semiconductors, Chiung-Wei Huang, Xiao You, Peter J. Diemer, Anthony Joseph Petty Ii, John E. Anthony, Oana D. Jurchescu, Joanna M. Atkin

Chemistry Faculty Publications

Charge transport in organic semiconductors is highly sensitive to film heterogeneity and intermolecular interactions, but probing these properties on the length scales of disorder is often difficult. Here we use micro-Raman spectroscopy to assign vibrational modes of isomerically pure syn and anti 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES ADT) by comparing to density functional theory calculations. With polarization-dependent measurements, we determine the orientation of crystallites in pure isomers. In mixed-isomer samples, we observe narrow linewidths and superposition spectra, indicating coexistence of isomerically pure sub-domains on length scales smaller than the probe area. Using the ring breathing modes close to 1300 cm⁻¹ as indicators …

I. Contorted Polycyclic Aromatic Hydrocarbons: Attempted Synthesis Of [12]Circulene Derivatives Ii. Synthesis And Characterization Of Novel [1]Benzothieno[3,2-B][1]Benzothiophene Derivatives, Jonathan Hollin

Graduate College Dissertations and Theses

There has been increasing interest in the development of organic materials due to their unique structural and electronic properties. Organic compounds have the advantage of being able to be deposited from solution, leading to low-cost, high-area electronics production. Contorted polycyclic aromatic hydrocarbons have been shown to have potential for use in organic field-effect transistors (OFETs) and organic photovoltaic devices (OPVs) due to their supramolecular properties and charge carrier mobilities. Thiophene-based materials have also shown great promise in OFETs due to their high charge carrier mobilities, stability during device operation, solubility in organic solvents, and structural versatility.

[n]Circulenes are a class …

Effect Of Molecular Side Groups And Local Nanoenvironment On Photodegradation And Its Reversibility, Nicole Quist, Mark Li, Ryan Tollefsen, Michael Haley, John Anthony, Oksana Ostroverkhova

Chemistry Faculty Publications

Degradation of organic semiconductors in the presence of oxygen is one of the bottlenecks preventing their wide-spread use in optoelectronic devices. The first step towards such degradation in functionalized pentacene (Pn) derivatives is formation of endoperoxide (EPO), which can either revert back to the parent molecule or proceed to molecule decomposition. We present the study of reversibility of EPO formation through probing the photophysical properties of functionalized fluorinated pentacene (Pn-R-F8) derivatives. Experiments are done in solutions and in films both at the single molecule level and in the bulk. In solutions, degradation of optical absorption and its partial recovery after …

Single Molecule-Level Study Of Donor-Acceptor Interactions And Nanoscale Environment In Blends, Nicole Quist, Rebecca Grollman, Jeremy Rath, Alex Robertson, Michael Haley, John E. Anthony, Oksana Ostroverkhova

Chemistry Faculty Publications

Organic semiconductors have attracted considerable attention due to their applications in low-cost (opto)electronic devices. The most successful organic materials for applications that rely on charge carrier generation, such as solar cells, utilize blends of several types of molecules. In blends, the local environment strongly influences exciton and charge carrier dynamics. However, relationship between nanoscale features and photophysics is difficult to establish due to the lack of necessary spatial resolution. We use functionalized fluorinated pentacene (Pn) molecule as single molecule probes of intermolecular interactions and of the nanoscale environment in blends containing donor and acceptor molecules. Single Pn donor (D) molecules …

Thermal Conductivities Of Organic Semiconductors, Yulong Yao

Theses and Dissertations--Physics and Astronomy

Organic semiconductors have gained a lot of interest due to their ease of processing, low-cost and inherent mechanical flexibility. Although most of the research has been on their electronic and optical properties, knowledge of the thermal properties is important in the design of electronic devices as well. Our group has used ac-calorimetric techniques to measure both in-plane and transverse thermal conductivities of a variety of organic semiconductors including small-molecule crystals and polymer blends. For layered crystals composed of molecules with planar backbones and silylethynyl (or germylethynyl) sidegroups projecting between the layers, very high interplanar thermal conductivities have been observed, presumably …

Quantitative Analysis Of The Density Of Trap States At The Semiconductor-Dielectric Interface In Organic Field-Effect Transistors, Peter J. Diemer, Zachary A. Lamport, Yaochuan Mei, Jeremy W. Ward, Katelyn P. Goetz, Wei Li, Marcia M. Payne, Martin Guthold, John E. Anthony, Oana D. Jurchescu

Chemistry Faculty Publications

The electrical properties of organic field-effect transistors are governed by the quality of the constituting layers, and the resulting interfaces. We compare the properties of the same organic semiconductor film, 2,8-difluoro- 5,11-bis (triethylsilylethynyl) anthradithiophene, with bottom SiO₂ dielectric and top Cytop dielectric and find a 10× increase in charge carrier mobility, from 0.17 ± 0.19 cm² V⁻¹ s⁻¹ to 1.5 ± 0.70 cm² V⁻¹ s⁻¹, when the polymer dielectric is used. This results from a significant reduction of the trap density of states in the semiconductor band-gap, and a decrease in the …

Time-And Polarization-Resolved Photoluminescence Studies Of Directional Coupling In Isolated Semiconductor Nanostructures, Joelle A. Labastide

Doctoral Dissertations

TIME-AND POLARIZATION-RESOLVED STUDIES OF DIRECTIONAL COUPLING IN ISOLATED SEMICONDUTOR NANOSTRUCTURES MAY 2015 JOELLE A. LABASTIDE, B.S. UNIVERSITY OF MASSACHUSESSTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMERST Directed by Professor Michael D. Barnes Development of new materials and assembly strategies for organic semiconductor-based optoelectronic materials is a problem of great interest worldwide, as researchers seek to resolve the questions pertinent to the creation of inexpensive, reliable, efficient, and stable active layer components. Organic semiconductors as the basis for photovoltaic active layers show significant promise for these applications. However, there is still much that needs to be understood about the molecular scale structural …

Photophysics Of Organic Semiconductors: From Ensemble To The Single-Molecule Level, Rebecca Grollman, Whitney E. B. Shepherd, Alexander Robertson, Keshab R. Paudel, John E. Anthony, Oksana Ostroverkhova

Chemistry Faculty Publications

We present photophysical properties of functionalized anthradithiophene (ADT) and pentacene (Pn) derivatives, as well as charge and energy transfer properties of donor-acceptor (D/A) pairs of these derivatives. All molecules studied were fluorescent and photostable enough to be imaged on the single-molecule level in a variety of polymeric and in a functionalized benzothiophene (BTBTB) crystalline host using room-temperature wide- field epifluorescence microscopy. Flexibility of functionalization of both guest (ADT, Pn) and host (BTBTB or polymer) molecules can be used for systematic studies of nanoscale morphology and photophysics of D/A organic semiconductor bulk heterojunctions, as well as in applications relying on FRET, …

Optical And Scanning Probe Studies Of Isolated Poly (3-Hexylthiophene) Nanofibers, Mina Baghgarbostanabad

Doctoral Dissertations

Plastic electronics have an essential role in the future technologies owing to their compelling characteristics such as light weight, biocompatibity, low cost fabrication, and tunable optoelectronic properties. However, the performance of polymer-based devices strongly depends on the efficiency of exciton formation and dynamics that are themselves strongly sensitive to polymer molecular packing and structural order. Therefore, the current challenge in achieving high efficiency is establishing a correlation between molecular packing and exciton coupling. P3HT nanofibers represent an attractive platform for studying optical and electronic properties of exciton coupling because their nominal (highly crystalline) internal chain packing structure is known. A …

Low-Temperature Phase Transitions In A Soluble Oligoacene And Their Effect On Device Performance And Stability, J. W. Ward, K. P. Goetz, A. Obaid, Marcia M. Payne, P. J. Diemer, C. S. Day, John E. Anthony, O. D. Jurchescu

Chemistry Faculty Publications

The use of organic semiconductors in high-performance organic field-effect transistors requires a thorough understanding of the effects that processing conditions, thermal, and bias-stress history have on device operation. Here, we evaluate the temperature dependence of the electrical properties of transistors fabricated with 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene, a material that has attracted much attention recently due to its exceptional electrical properties. We have discovered a phase transition at T = 205 K and discuss its implications on device performance and stability. We examined the impact of this low-temperature phase transition on the thermodynamic, electrical, and structural properties of both single crystals and thin films …

Synthesis And Characterization Of Some Thallium Salt Complexes, Levi Dopierala

Masters Theses & Specialist Projects

Research into conductive organic and organometallic polymers began in 1977 when Heeger, Macdiarmid, and Shirakawa first doped polyacteylene with Iodine. They found that this doping granted the polymer metallic properties increasing conductivity by 11 orders of magnitude.[1] Unfortunately, polyacteylene is highly air-sensitive making it difficult to work with and limiting its applications. Therefore, current research is focused on synthesizing new organic and organometallic conductive polymers. The drive to discover these new polymers stems from their application flexibility and their low production cost.

Reported here is the synthesis of novel organometallic polymer precursors. Lead by Dr. Chad Snyder a library of …

Topography-Guided Spreading And Drying Of 6,13-Bis(Triisopropylsilylethynyl)-Pentacene Solution On A Polymer Insulator For The Field-Effect Mobility Enhancement, Chang-Min Keum, Jin-Hyuk Bae, Min-Hoi Kim, Hea-Lim Park, Marcia M. Payne, John E. Anthony, Sin-Doo Lee

Chemistry Faculty Publications

We report on the enhancement of the field-effect mobility of solution-processed 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) by unidirectional topography (UT) of an inkjet-printed polymer insulator. The UT leads to anisotropic spreading and drying of the TIPS-pentacene droplet and enables to spontaneously develop the ordered structures during the solvent evaporation. The mobility of the UT-dictated TIPS-pentacene film (0.202 ± 0.012 cm²/Vs) is found to increase by more than a factor of two compared to that of the isotropic case (0.090 ± 0.032 cm²/Vs). The structural arrangement of the TIPS-pentacene molecules in relation to the mobility enhancement is described within an …

Fluorinated Arene, Imide And Unsaturated Pyrrolidinone Based Donor Acceptor Conjugated Polymers: Synthesis, Structure-Property And Device Studies, Arawwawala Don T. Liyanage

Theses and Dissertations--Chemistry

FLUORINATED ARENE, IMIDE AND LACTAM-FUNCTIONALIZED DONOR ACCEPTOR CONJUGATED POLYMERS: SYNTHESIS, STRUCTURE-PROPERTY AND DEVICE STUDIES

After the discovery of doped polyacetylene, organic semiconductor materials are widely studied as high impending active components in consumer electronics. They have received substantial consideration due to their potential for structural tailoring, low cost, large area and mechanically flexible alternatives to common inorganic semiconductors. To acquire maximum use of these materials, it is essential to get a strong idea about their chemical and physical nature. Material chemist has an enormous role to play in this novel area, including development of efficient synthetic methodologies and control the …

On-Metal Synthesis Of Some Aryl Substituted Rhenium Η5 Cyclopenta[C] Pyridazyl Complexes, Phenahas Gandu Sriramulu

Masters Theses & Specialist Projects

Heterocyclic organic and organometallic compounds (e.g. polypyrrole) and their derivatives have been of great interest for conductive polymers due to their novel properties and environmental stability as compared to non-aromatic analogs (e.g. polyacetylene). We are interested in synthesizing organometallic pyridazines and rhenium pyridazyl complexes for polymer research. SeveraI5,6-fused ring pyridazines (1,2-CsH3(CRNH)(CRN) have been synthesized and characterized. Additionally, pyridazyl complexes of rhenium were synthesized in three steps beginning from fulvenes 1,2-CsH3(COHR)(COR). On-Metal synthesis and characterization of (Re(CO)3 {1,2- CSH3(CRN)(CRN)}] (R=C6RtOMe, C6RtCI, C4H30) and some off-metal pyridazines are reported here. Our research is focused on synthesis of a variety of 5,6- fused …

Substituent Effect On The Electronic And Assembling Properties Of Asymmetric Phenazine Derivatives, Bin Cao

UNLV Theses, Dissertations, Professional Papers, and Capstones

Currently, one-dimensional (1-D) nanostructures have drawn much interest because of their potential applications for nanoscale optoelectronic devices. Self-assembly (SA) based on π-conjugated systems through various intermolecular interactions has been widely used to produce 1-D nanostructure. Morphology of the assembled structures can be modified by incorporating substituents, which provide additional secondary interactions. Meanwhile, those substituents also influence the electronic properties of the molecules. Previous studies have made little effort to systematically study subsistent effects on both electronic and SA properties.

The primary objective of this research is to generate controllable 1-D structures through SA, and to provide a fundamental understanding of …

Proposed Route To Cyclopenta[C]Thiophenes Via Activated Methylene, Vineet V. Karambelkar

Masters Theses & Specialist Projects

The synthesis of cyclopenta[c]thiophenes has been sparsely reported in the literature owing to several difficulties involved in their synthesis. The present work involves the proposed synthesis of cyclopenta[c]thiophenes and their precursors using activated methylene. Cyclopenta[c]thiophene compounds show promise in the field of polymer and catalysis chemistry. These substituted polythiophenes are potential organic semiconductors and anti-tumor agents. The research presented shows the successful and novel conversion of 3,4-bis(chloromethyl)-2,5-dimethylthiophene and 3,4-bis(bromomethyl)-2,5-dimethylthiophene to a fused 5,5'-fused membered ring which is the precursor to cyclopenta[c]thiophene the sulfone ester, 5-carbomethoxy-5- phenylsulfonyl-1,3-dimethyl-5,6-dihydro-4H-cyclopenta[c]thiophene, in just two steps as compared to four steps previously reported in the literature. …