Silicon-Containing Organic Conjugated Materials for Light Emitting Diodes

This thesis contains a study of polymer light emitting diodes (PLEDs) for commercial use within blue organic light-emitting diode (OLED) display technologies. The introduction chapter outlines the aims and synthetic strategies / targets employed during the research and gives background information as to the historical development of OLEDs and PLEDs. The first chapter of research involves the synthesis of several alternating co-polymers of dibenzosilole (a previously reported monomer used in light emitting devices), along with the prerequisite monomers. These co-polymers have been fully characterised and their optoelectronic properties evaluated. The energy levels of the co-polymers (HOMO / LUMO) were measured, then compared with each other and used to establish correlations between these values and the use of co-monomers and the polymer backbone linearity. By tuning the energy levels of conjugated polymers, it is possible to alter both the energy of the light emitted (and therefore the colour) and also improve the charge-injection balance within the OLED device, thereby improving lifetimes and performance. This research was primarily concerned with blue light-emission, therefore these energy level studies were conducted with a view to achieving blue light emission with the desired CIE coordinates and luminance. The novel co-polymers were used to fabricate several prototype OLED devices and the performance of these has been evaluated. The second chapter of research contains a study of several novel silicon-containing monomer structures, for incorporation into conjugated PLEDs. The first structure is a disilaanthracene derivative and the attempted synthesis of this monomer is reported. The other two monomers are based on spirosilabifluorene and the syntheses and full characterisations are reported. Attempts at the coupling of these monomers were made, using several different known coupling reactions including Suzuki, Stille and Kumada. The attempted coupling products were simple trimers, using 9,9-dioctylfluorene as a co-monomer. These were to be used in small molecule organic light-emitting diodes (SMOLEDs). The outcomes of these coupling reactions are described

New Diketopyrrolopyrrole(DPP)-Based Conjugated Polymers Prepared upon Palladium Catalyzed Polymerization and Electropolymerization Reactions

Synthesis and characteristic properties of new conjugated polymers and polyelectrolytes containing DPP-units in the main chain are described. The polymers are synthesized upon palladium-catalyzed Suzuki, Stille and Buchwald-Hartwig polycondensation and electropolymerization. Characteristic properties such as molecular weight, structure, optical and electrooptical properties of the polymers are studied using gel permeation chromatography, spectroscopic methods (UV/vis, Fluorescence, NMR spectroscopy), cyclic voltammetry and spectroelectrochemical characterization. Using the Suzuki, Stille and Buchwald-Hartwig coupling, conjugated polymers are synthesized from dibromo-DPP or the boronic ester of DPP and derivatives of the carbazole (CBZ), triphenylamine (TPA), benzothiadiazole (BTZ), thiophene (TH), bithiophene (BTH), 3,4-ethylenedioxythiophene (EDOT), pyrene (PYRE) or N,N'-diphenyl-1,4-phenylene diamine (PDA). The molecular weights of the resulting polymers are between 4.3 and 16.5 kDa. The polymers are soluble in solvents such as toluene, chloroform or THF forming red to purple solutions with strong photoluminescence. Compared with the DPP monomer, the optical properties of the polymers are bathochromically shifted due to the increase of the conjugated system. Polymers in solution exhibit absorption maxima between 506 and 560 nm, and fluorescence maxima between 585 and 635 nm. The polymer P-DPP-TPA exhibits a photoluminescence quantum yield of 85 %, which is the highest value reported for DPP containing conjugated polymers so far. Polymers of DPP and BTH, PDA and PYRE exhibit reversible electrochromic properties upon electrochemical oxidation and reduction. The abrupt colour changes from purple to dark blue to black-green are observed. Furthermore, a series of electropolymerizable DPP containing monomer have been successfully prepared using Suzuki, Stille or Buchwald-Hartwig coupling. The in-situ formed polymer films are robust and insoluble in common solvents. They exhibit a very good stability during oxidation reduction cycles together with electrochromic properties. The polymer films are useful as active materials in electrochromic devices showing colour changes from blue to transparent, brown-red to olive-green, purple-red to brown-red, and colourless to green. Conjugated polyelectrolytes were synthesized from bis-bromohexyl-DPP or bis-sulfonylbutyl-DPP using Suzuki and Buchwald-Hartwig coupling. The resulting cationic and anionic polyelectrolytes are readily soluble in water and polar organic solvents such as methanol and DMSO. The polymers are non-luminescent in water, but exhibit photoluminescence quantum yields between 6.2 % and 49 % in DMSO