Strongly Polarized and Efficient Blue Organic Light‐Emitting Diodes Using Monodisperse Glassy Nematic Oligo(fluorene)s

Abstract

ment effect at the higher energy side more easily than quantum wires, we expect the SiNTs to be more useful for future optoelectronic devices. ExperimentalPorous alumina templates were prepared by an anodization process. An aluminum foil (99.99 %, 0.13 mm thick, Aldrich) was electropolished in a perchloric acid/ethanol solution (ethanol (95 vol.-%)/perchloric acid (70 vol.-%) = 5:1) at 9 C at a constant dc (direct current) voltage of 18 V for 1.5 min. This cleaned aluminum sheet was then anodized in a 0.3 M oxalic acid solution at 5 C at a constant applied voltage of 40 V for 6 h. The resultant aluminum oxide layer was removed by dipping into an aqueous mixture of phosphoric acid (6 wt.-%) and chromic acid (1.8 wt.-%) at 60 C. The second anodization was performed for 20 min at the same conditions in order to form a regular pore array of hexagons. After pore widening by dipping into an aqueous solution of 0.1 M phosphoric acid for 10 min, we performed heat treatment to enhance the crystallinity of the alumina templates at 500 C for 30 min under Ar atmosphere. A regular array of hexagonal porous alumina was formed on both surfaces of aluminum film. This template was brought into the MBE chamber to grow SiNTs, where the chamber was evacuated to a pressure of 5 10 ±10 torr. The Si atoms/clusters were supplied for 10 min by electron-beam evaporator with a growth rate of 0.07 s ±1. The substrate temperature was maintained at 400 C in order to prevent the aluminum layer from being melted. After growth, the sample was further heat treated at 600 C or 750 C under ambient conditions for oxidation.The morphology of the SiNTs was observed by the field-emission scanning electron microscope (FESEM, JEOL-JSM6770F). High-resolution transmission electron microscopy (HRTEM, JEOL-JEM3011, 300 keV) was also used to determine the atomic details of the SiNTs. For HRTEM observations, small pieces of SiNTs were peeled off from the alumina surface and suspended, followed by further dispersion in isopropanol simply by stirring and sonication. The solvent containing the SiNTs was dropped on a holey carbon micro-grid. The photoluminescence (PL) spectra were measured with a He±Cd laser (325 nm). The laser beam diameter was about 0.3 mm with a power of 10 mW.

Synthesis and Characterization of Light-Emitting H-Bonded Complexes and Polymers Containing Bis(pyridyl) Emitting Acceptors

“…35 Besides, some other higher polarization ratios and dichroic ratios of emissions are reported as well. 23,36 Polymer light emitting diodes containing pyridine 37,38 and thiophene 39 repeat units are of considerable interest in the areas of electron transporting. The photoluminescence (PL) of the polymers 8,40 and copolymers 41,42 due to hydrogen bonds within and between the polymer chains are reported.…”

Organic Polarized Light‐Emitting Diodes via Förster Energy Transfer Using Monodisperse Conjugated Oligomers

“…The polarized OLED devices, ITO/PEDOT:PSS (40 nm)/doped heptafluorene (53 nm)/TPBI (30 nm)/LiF (0.5 nm)/Mg:Ag at 20:1 (210 nm) (where ITO = indium tin oxide, PEDOT = poly(3,4-ethylenedioxythiophene), PSS = poly(styrene sulfonic acid), and TPBI = 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene), were prepared and characterized following the same procedures as reported previously. [30] The alignment layers consisted of a uniaxially buffed PEDOT:PSS film. Both the donor and acceptor molecules are expected to orient themselves along the buffing direction.…”

Liquid crystalline conjugated polymers and their applications in organic electronics

“…Other alignment layers include rubbed poly(3,4-ethylenedioxythiophene) (PEDOT), 27,45,75,76 poly(vinylalcohol) (PVA), 67 PPV, 94 poly(N-vinylcarbazole) (PVK), 95 and other photoaligned polymers. 77,96,97 PEDOT is wellknown for its hole-transporting property and extensively used in light-emitting devices.…”

“…In many ways, oligomers own better optical properties and are easier to manipulate compared with their corresponding polymers. Several conjugated oligomers with LC properties have been synthesized to study their photo-physical and self-assembled properties, including oligo(p-phenylenevinylene) (OPV), [65][66][67][68][69][70][71][72][73][74] oligofluorene, [75][76][77][78][79][80] and oligo(p-phenyleneethynylene).…”