Marie D'Iorio

Synthesis and characterization of a novel AlQ3-containing polymer

In this article, the synthesis of a tris(8-hydroxyquinoline)aluminum (AlQ3)-containing poly(arylene ether) (4) is reported. The presence of AlQ3 pendants in polymer 4 is confirmed by NMR, ultraviolet–visible, photoluminescence, and gel permeation chromatography analyses. This is the first report of the attachment of AlQ3 complexes as side chains to a polymer. Polymer 4 has a glass-transition temperature of 217.8 °C and is thermally stable with a 5% weight-loss temperature greater than 500 °C under nitrogen, as determined by differential scanning calorimetry and thermogravimetric analyses, respectively. Polymer 4 is quite soluble in common organic solvents, such as tetrahydrofuran, N,N-dimethylacetamide, and CHCl3. A composite that is 80 wt % polymer 4 and 20 wt % AlQ3 forms a transparent and tough film when cast from its chloroform solution. The application of this AlQ3-containing polymer in light-emitting diodes is under investigation.

Organic light emitting diodes based on end-substituted oligo(phenylenevinylene)s

Abstract We report our investigation of the electroluminescent properties of multilayer organic light emitting devices using a series of three-phenyl-ring oligo(phenylenevinylene)s with poly(alkyleneoxy) electron-donors and hexylsulfonyl electron-acceptors as emitting materials. The emission color varies from blue to green depending on the substituted end-groups in the molecules. The insertion of hole blocking and electron injecting layers significantly improves the electroluminescent efficiency and extends the operational life time. The maximum electroluminescence efficiency reached is 1.9 cd/A for the blue diodes, and 2.3 cd/A for the blue-green diodes.

A passive matrix addressed organic electroluminescent display using a stack of insulators as row separators

In order to use the impressive performances of organic light emitting diodes (OLEDs) in high-resolution flat-panel displays (FPDs), ways must be found to circumvent their incompatibility with standard microfabrication techniques. To integrate organic compounds in a passive matrix, one must be able to pattern the top electrode in rows without exposing them to any processing. We deposited a stack of three different insulators in one process in a commercial plasma-enhanced chemical vapor deposition (PECVD) tool, patterned it in a single lithography step and in a single wet etch step. The top insulator etches slowest, so the stack gets undercut. When organics and the top electrode are thermally evaporated on this pattern, they are physically discontinuous at the edges of the overhanging insulator. The lowest insulator etches slower than the middle one, so it tails out and prevents short circuits when the top electrode flows over the edge of the organic layers. This process combines simplicity and high resolution, two prerequisites for OLEDs to compete with existing FPD technologies.

Synthesis of poly(arylene ether)s containing hole-transport moieties from an isocyanate masked bisphenol

The design and synthesis of novel charge (hole- or electron-) transport materials have been the focus of much research in recent years because of their wide variety of applications. In this study, three high molecular weight poly(arylene ether)s, 6a–c, containing naphthyl-substituted benzidine moieties have been synthesized from carbamates derived from bisphenols. After masking with n-propyl isocyanate, the carbamate is stable, can be readily purified by recrystallization from toluene, and can be polymerized directly with difluoro compounds under mild conditions. The resulting polymers possess high glass-transition temperatures, excellent thermal stability, and good film-forming properties. In comparison, the poly(arylene ether)s 6a′–c′, synthesized from unprotected bisphenol, have lower molecular weights and wider polydispersity and contain some brown impurities. Preliminary experiments show that both 6a and 6a′ can function well as hole-transport materials in light-emitting diodes.

Luminescence properties of end-substituted oligo(phenylenevinylene)s

Abstract We have used three soluble three-phenyl-ring oligo(phenylenevinylene)s (OPV(1)s) with poly(alkyleneoxy) electron donors and hexylsulfonyl electron acceptors to investigate the end-substitution effect. Besides the increase in solubility, the end substitution is found effective in fine tuning the absorption and emission properties. Symmetrically substituted OPV(1)s, with the same donor or acceptor end-groups, show a small red shift in their absorption and emission spectra as compared to the unsubstituted OPV(1). Asymmetrically substituted OPV(1), with a donor at one end and an acceptor at the other, shows a larger red shift in both the absorption and emission spectra due to the increased π-electron delocalization associated with the “push–pull” effect of the donor and acceptor in the molecule.

Blue double layer devices obtained by spin-coating

Abstract Double spin-coated electroluminescent (EL) devices have been prepared by combining a blue EL arylamine-based hole transport polymer (STPD-QP) in the first spin-coated layer with a blue EL oxadiazole-based electron transport polymer (SP-OX) in the second layer. The luminance and efficiency of these devices are improved by adding PBD, a low molecular weight electron transport oxadiazole derivative, as a solute in the SP-OX layer. Doing so, maximum luminance of ∼1500 cd/m 2 and quantum efficiencies up to 0.5% are obtained. Similar luminances cannot be reached by using only solid solutions of PBD in A435, a rather insulating host polymer.

New red–orange phosphorescent/electroluminescent cycloplatinated complexes of 2,6-bis(2′-indolyl)pyridine

Three novel cyclometalated complexes of 2,6-bis(2′-indolyl)pyridine (H2BIP), Pd(BIP)(Py) (Py = pyridine) (1), Pt(BIP)(SMe2) (2) and Pt(BIP)(Py) (3) have been synthesized and characterized structurally. The Pd and Pt centers in these compounds are four-coordinate with a square planar geometry. The BIP ligand acts as a tridentate chelate to the metal center, and the dimethyl sulfide and the pyridine ligand bind to the metal center as terminal ligands. Compound 1 has no luminescence. Compounds 2 and 3 display bright orange luminescence either at 77 K in a frozen CH2Cl2 solution or at ambient temperature in a polymer matrix (e.g. poly(carbonate) or PVK). The emission maxima for 2 and 3 in the frozen CH2Cl2 solution are at λ = 572 and 589 nm, respectively. The emission spectra of 2 and 3 in the polymer matrix are very similar with λmax = 585 nm. The luminescence of 2 and 3 is phosphorescent as supported by the emission lifetimes of 2 (94(1) μs in CH2Cl2 at 77 K, 22.1(1) μs in poly(carbonate) at 298 K) and 3 (44(1) μs in CH2Cl2 at 77 K, 19(1) μs in poly(carbonate) at 298 K). Based on the luminescence properties of the free ligand and the results of molecular orbital calculations, we propose that the luminescence of 2 and 3 is most likely due to a π → π* transition with a significant dπ orbital contribution from the Pt(II) center to the π level. Electroluminescent devices using compound 3 as the emitter and PVK as the host and hole transport material have been fabricated successfully.

Synthesis and Characterization of Poly( N -alkyl-2,7-carbazole)s: Blue Light-Emitting Materials

The synthesis of a new class of π-conjugated based on N -alkyl-2,7-carbazole is reported. Two different synthetic pathways were used to obtain 2,7-functionalized carbazole units. The first pathway leads to N -alkyl-2,7-dichlorocarbazole which undergoes a Yamamoto coupling to obtain the homopolymer. The second synthetic method provides N -alkyl-2,7-diiodocarbazole. This monomer allows the utilization of more versatile synthetic tools such as Suzuki and Stille couplings to obtain highly regioregular copolymers. Poly( N -(2-ethylhexyl)-2,7-carbazole) (PEHC) prepared using Yamamoto coupling shows strong pure blue photoluminescence (437 nm) and electroluminescence (432 nm, 225 cd/m 2 ) with no excimer formation.

Lanthanum-based cathodes for organic light-emitting devices

The fabrication of organic light emitting diodes with vacuum sublimed molecules is emerging as a competitive flat panel display alternative because of brightness, efficiency and operating lifetimes of these devices. The requirement for a low work function metal as a cathode limits the choice of materials to reactive elements such as magnesium, calcium, lithium that can be alloyed or co-deposited with silver or aluminum for greater stability and lifetime of the device. From the scandium-subgroup of elements, we have investigated lanthanum as a potential cathode because preliminary studies indicated that the electroluminescence onset could occur as low as 4 volts. Current-voltage, Auger spectroscopy and spectro-photometric data will be presented on standard devices using indium tin oxide, triphenyl diamine derivative and aluminum quinolinate and lanthanum-based cathodes.