This thesis reports the spectroscopic and computational studies of two classes of compounds, which have applications in new optoelectronic materials technology. Substituted ligands of dipyrido-[3,2a:2�,3�c]phenazine (dppz), and their Cu(I), Re(I) and Ru(II) complexes have utility in organic electroluminescent devices. A series of Zn(II) tetraphenylporphyrins with conjugated functional groups at the β-position have been used with success in liquid heterojunction dye-sensitized solar cells. The vibrational spectra and optoelectronic properties of the two classes were investigated using Raman, resonance Raman and transient resonance Raman spectroscopy, in conjunction with density functional theory methods. Density functional theory frequency calculations were used to aid vibrational mode assignments for the dppz compounds, and show close agreement with the experimental non-resonance Raman spectra. The enhancement of modes which are localized on differing sections of the ligand was identified. The nature of the absorbing chromophores for the dppz ligands and complexes was established using resonance Raman spectroscopy in concert with vibrational assignments from calculations. Transient resonance Raman spectra of the ligands provided spectral signatures for the triplet ligand-centred state; these features were observed in the TR� spectra of the metal complexes, along with other features attributable to MLCT states. Electroluminescent devices were fabricated using the dppz ligands and complexes as emissive dopants, and their properties investigated. The optoelectronic behaviour of the devices was found to be influenced by the mechanism of exciton formation on the dopant. The device properties were also dependent on the dopant concentration, the concentrations of other components and the driving voltage. The electronic structure of the porphyrin compounds was investigated using time-dependent density functional theory methods. Comparison of calculated optical transitions with experimental data shows that the calculations predict trends in the optical absorption spectra with change of functional group and with increase in conjugation chain length. The calculations suggest that the electron-withdrawing substituent decreases the configuration interaction effect by breaking the degeneracy of the two lowest unoccupied MOs, and other configuration interaction effects come into play involving other frontier MOs. Interrupting the conjugation of the functional group is shown to mitigate the breakdown of the configuration interaction. The perturbation of the normal electronic structure of the porphyrin by the substituent was also investigated using resonance Raman spectroscopy. Vibrational analysis identified bands due to the substituent, implying coupling between the porphyrin and substituent chromophores. Changes in frequency of porphyrin core modes due to the differing substituents and different metal centres were reproduced by density functional theory calculations. This project has allowed the spectroscopic investigation of the active optical states in a number of polypyridyl and porphyrin compounds, and determined the efficacy of DFT and TDDFT calculations to predict the properties of these compounds.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 110-118).

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on November 21, 2007) Vita. Includes bibliographical references.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006. / Dr. C. P. Wong, Committee Member ; Dr. C. David Sherrill, Committee Member ; Dr. Thomas M. Orlando, Committee Member ; Dr. Mostafa A. El-Sayed, Committee Member ; Dr. Robert M. Dickson, Committee Chair.

abstract: Group-IV semiconductor alloys are of interest for Si-integrated optoelectronic applications due to the band gap tunability and enhanced optical capabilities that can be achieved through compositional tuning. This work advances the field by presenting a systematic study of the optical and electronic properties of Ge1-ySny and analogous Ge1-x-ySixSny alloys. The fundamental direct and indirect band gaps of Ge1-ySny materials are measured by room temperature photoluminescence in samples containing 0 ≤ y ≤ 0.11 and a transition to direct gap materials is found to occur at yc = 0.087. This result is enabled by the development of sample growth and processing protocols that produce high-quality materials epitaxially on Ge-buffered Si(100) substrates. Strategies to optimize the optical performance are explored by varying the film thickness, thermal and surface treatments, and n-type doping. The electrical and optical properties of diodes based on these materials are characterized by current-voltage, optical responsivity, and electroluminescence measurements. These show improved optical performance near yc with tunable emission out to 2500 nm. Measuring the carrier lifetimes in devices with strain relaxed and fully strained interfaces show significantly longer lifetimes in the fully strained case. The direct and indirect band gaps of Sn-rich (y > x) Ge1-x-ySixSny materials are measured by room temperature photoluminescence on optimized samples. These data confirm a transition to direct gap materials occurs for the ternary alloy as well. Devices based on compositions 0.02 ≤ x ≤ 0.10 and 0.03 ≤ y ≤ 0.11 are characterized by current-voltage, optical responsivity, and electroluminescence measurements and show competitive performance with analogous devices based on Ge1-ySny materials. A detailed study of the direct gap in Ge1-xSix alloys gives parameters crucial en route to a global description of the Ge1-x-ySixSny fundamental band gaps. Archetypal laser device designs on Si are explored by fabricating degenerate pn junction diodes and highly doped waveguide devices based on high-quality Ge1-ySny materials. The diodes showed tunnel-like current-voltage characteristics and tailored electroluminescence based on the doping profile. The waveguides demonstrate emission under optical stimulation. / Dissertation/Thesis / Doctoral Dissertation Physics 2015

Orientador: Teresa Dib Zambon Atvars / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-10T13:29:22Z (GMT). No. of bitstreams: 1 Cossiello_RafaelDiFalco_D.pdf: 19466365 bytes, checksum: 4613f44ad7300b66e793fa6de43b2c82 (MD5) Previous issue date: 2007 / Resumo: O copolímero SAA (poli(estireno-co-ácido acrílico-co-1-metacrilato de pirenilmetila)) foi sintetizado por via radicalar em agua e caracterizado por analises termicas (DSC, TGA), espectroscopicas (NMR C e H, UV-VIS, FTIR, fluorescência estacionária e resolvida no tempo) e elétricas (eletroluminescência). As blendas com poli[2-metóxi-5-(2¿-etilóxi)-p-fenilenovinileno] MEH-PPV foram estudadas desde 0,01; 0,05; 0,10; 0,50; 1,0; 10,0; 25; 50; 75 e 90 (% em massa) de MEH-PPV em SAA para ánalise da evolucao da morfologia por microscopia óptica, de fluorescência e eletrônica de varredura em espessuras de 70 mm (fratura criogênica) e 70 nm (espessura do dispositivo). Em baixas concentracões os domínios de MEH-PPV se apresentam em forma de núcleos dispersos e empacotados e conforme se aumenta a concentracao de MEH-PPV, observa-se que há a coalescência destes núcleos até a formação de uma fase interconectada de uma rede tridimensional. As medidas de difração à altos angulos mostram que há uma preferência de orientação do MEH-PPV ao longo do substrato e nao influencia a isotropia do SAA devido a baixa miscibilidade entre estes polímeros. As unidades de 1-pirenil metila foram utilizadas para avaliar a polaridade do microambiente e o mecanismo de transferencia de energia entre o doador (SAA) e o receptor (MEH-PPV). A dependência do tempo de fluorescência das unidades 1-pirenilmetila com a concentracao do MEH-PPV fornece subsídios para concluir que ocorre interpenetração de cadeias e, portanto uma baixíssima solubilidade entre os dois polímeros. O melhor desempenho de eletroluminescência foi do dispositivo preparado a partir da mistura 50:50 de MEH-PPV:SAA, cuja corrente elétrica foi aumentada em 2,5 vezes e a luminância em 4 vezes se comparado com o dispositivo de MEH-PPV puro. A morfologia de fase interconectada se mostrou importante para um melhor processo de transporte de cargas. O copolímero de SAA permitiu uma melhor injeção de cargas devido aos grupos carboxila presentes das unidades de ácido acrílico / Abstract: The copolymer SAA poly(styrene-co- acrylic acid -co-1-pyrenylmethyl methacrylate) was synthesized by radical emulsion in water and characterized by thermal analyses (DSC, TGA), spectroscopic (NMR 13C and 1:00, UV-VIS, FTIR, stationary and time-resolved fluorescence) and electric (electroluminescence). The blends with poly[2-methoxy-5(2'ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) were studied from 0. 01; 0. 05; 0.10; 0.50; 1.0; 10.0; 25; 50; 75 and 90 (% in mass) of MEH-PPV in SAA to analyze the morphology evolution by optical, epifluorescence and electronic microscopy. The films were prepared in two thicknesses: one around 70 mm to be analyzed by cryogenic fractures and 70 nm, to be comparable with the device thickness. In low concentrations the domains of MEH-PPV appears dispersed nuclei and accrete when the concentration of MEH-PPV is increased forming an interconnected phase. The diffraction measures (WAXD) show a preference orientation of MEH-PPV along the substrate plane and it do not influences the SAA due the low miscibility between each other. The increase of the MEH-PPV concentration showed a redshift on electroluminescence spectrum due the inner filter and auto-absorption and re-emission effects. The units of 1-pyrenylmethyl were used to evaluate the polarity of the microenvironment and the mechanism of energy transfer of among the donor (SAA) and the acceptor (MEH-PPV). The timedependence of fluorescence with the increase of MEH-PPV concentration show that occurs an chain interpenetration following the fluorescence non-radiative energy transfer model. The best electroluminescent device was prepared using the mixture 50:50 of MEH-PPV:SAA. The interconnected phases are important for a better process of charge transport. The copolymer SAA allowed for a dilution effect avoiding the aggregation process and facilitating the charge injection processes. This technology of polymeric blends gave good results the increase of the luminance intensity and reduction of the voltage operation / Doutorado / Físico-Química / Doutor em Ciências

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This thesis is dedicated to developing novel charged Pt(II) complexes and exploring their applications in electroluminescence, bio-imaging and the preparation of soft salts. At the beginning, a brief introduction about the development of ionic transition metal complexes and an overview of their applications in electroluminescence, bio-imaging and soft salts are presented. In chapter 2, a series of anionic Pt(II) complexes were successfully synthesized and fully characterized for their application in electroluminescence with relatively small current density. All the complexes show highly intense emission from blue to red in the solid state but is almost non-emissive in solution. The obtained single crystal data show that the anionic Pt(II) complexes exhibit very large Pt-Pt separation of over 10 Å in the crystal packings due to the bulky counterion [N(n-C4H9)4]+. The strong interactions between adjacent [Pt(C^N)(CN)2]- is thus absent in the solid state and this is considered as the main reason for the different properties in solution and solid state of these anionic complexes. This kind of Pt(II) anionic complexes has also found application in electroluminescence with relatively small current density. A series of novel water-soluble cationic Pt(II) complexes have also been designed and synthesized in chapter 3. Their photophysical properties in both water solution and solid state were investigated. Some of the cationic Pt(II) complexes have been selected to be applied in cell imaging in both live human hepatoma cells (BEL-7402) and mouse embryonic fibroblast (MEF) cells. The results show that these complexes have a much higher cellular uptake in BEL-7402 cells (tumor cells) than in MEF cells (normal cells), indicating these complexes are promising probes for tumor cell imaging. All of the cationic Pt(II) complexes show very low cytotoxicity at low concentration and the cell viability is still assessed to be high even when the concentration increases to 10 μM. The localization of the complexes turned out to be in the cytoplasm and accumulate near the cell nucleus. Attempts have been made to obtain efficient deep-red or NIR Pt(II) complexes by taking advantages of the Pt-Pt interactions in chapter 4. Two Pt(II) soft salts, SS1 and SS2 with bright emission at 674 and 718 nm, have been successfully prepared and characterized. The crystal packing shows a short separation between the two Pt atoms of 3.476 Å and the average distance of two planes of the cyclometalated ligands is 3.360 Å, indicating the existence of strong intramolecular Pt-Pt and π-π interactions. It is the first examples of Pt(II) soft salts bearing strong Pt-Pt interactions and π-π stacking and this has opened a versatile and facile avenue to prepare efficient NIR Pt(II) emitters by taking advantages of the Pt-Pt interactions. SS2 shows different emission in PEG with different concentration and excitation wavelength, indicating their potential application in optical data storage. The electrochromic properties of SS2 have also been investigated considering that the soft salt consists of ions with opposite charges, which suggests the soft salt could be promising candidate for electrochromic and optoelectronic material. The Pt(II) soft salt has also been used as NIR in-vivo imaging probe. Chapters presents the concluding remarks and points out some further work that could be done in the future. The experimental details are displayed in Chapter 6.

III-nitride direct bandgap semiconductors have attracted significant research interest due to their outstanding potential for modern optoelectronic and electronic applications. However, the high cost of III-nitride devices, along with low performance due to dislocation defects, remains an obstacle to their further improvement. In this dissertation, I present a significant enhancement of III-nitride devices based on emerging materials. A promising substrate, (-201)-oriented β-Ga2O3 with unique properties that combine high transparency and conductivity, is used for the first time in the development of high-quality vertical III-nitride devices, which can be cost-effective for large-scale production. In addition, hybridizing GaN with emerging materials, mainly perovskite, is shown to extend the functionality of III-nitride applications. As a part of this investigation, high-performance and high-responsivity fast perovskite/GaN-based UV-visible broadband photodetectors were developed. State-of-the-art GaN epilayers grown on (-201)-oriented β-Ga2O3 using AlN and GaN buffer layers are discussed, and their high optical quality without using growth enhancement techniques is demonstrated. In particular, a low lattice mismatch (⁓4.7%) between GaN and the substrate results in a low density of dislocations ~4.8Å~107 cm−2. To demonstrates the effect of (-201)-oriented β-Ga2O3 substrate on the quality of III-nitride alloys, high-quality ternary alloy InxGa1−xN film is studied, followed by the growth of high quality InxGa1−xN/GaN single and multiple quantum wells (QWs). The optical characterization and carrier dynamics by photoluminescence (PL) and time-resolved PL measurements were subsequently performed. Lastly, to investigate the performance of a vertical emitting device based on InGaN/GaN multiple QWs grown on (-201)-oriented β-Ga2O3 substrate, high-efficiency vertical-injection emitting device is developed and extensively investigated. The conductive nature of the substrate developed as a part of this study yields better current and heat characteristics, while its transparency ensures high light extraction. The straightforward and direct growth process employed does not require a high-cost complex fabrication process. Finally, a broadband photodetector composed of the emerging CH3NH3PbI3 perovskite with the p-GaN, is developed. The findings reported in this dissertation demonstrate the superior performance of CH3NH3PbI3/GaN photodetectors produced by simple and cost-effective solution processed spray-coating method. In particular, it is demonstrated that perovskite/GaN device can work as a self-powered photodetector.

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