Blue Polarized Electroluminescence from a Liquid Crystalline Polyfluorene

Abstract

Highly polarized electroluminescence from a liquid‐crystal polymer device, based on a branched polyfluorene with a branched side chain, is demonstrated here as a further step towards the use of organic electroluminescent (EL) devices as backlights in conventional liquid‐crystal displays. The modification of a polyimide (PI) for hole conduction by addition of a suitable filler at moderate concentration is reported and the performance of a device containing such a rubbed, hole‐conductor‐filled PI layer as the alignment layer is compared with that of a device with a PI‐only alignment layer.

Relating the physical structure and optical properties of conjugated polymers using neutron reflectivity in combination with photoluminescence spectroscopy

“…18 For the PF film, we measured the NR profiles at RT, then 120°C, RT, 220°C, and then RT again. The corresponding NR profiles of the PF film are shown in Fig.…”

Polarized organic electroluminescence: Ordering from the top

“…In a previous report on EL from aligned PF2-6, where the polymer was aligned by direct contact with an underlying polyimide film, the DR calculated from the ratio of the peak emission parallel and perpendicular to the alignment layer was 15. 5 For the single layer device used here the ratio of the EL peaks was 19 at 447 nm showing that the top-down approach is at least as good as the bottom up approach for aligning poly͑fluorene͒s. The dramatic difference though be- tween the two methods of alignment is in the device performance.…”

“…The most common method is a bottom-up approach, where an alignment layer is positioned between the electrode and the emissive layer. [3][4][5][6] The alignment layers used in this bottom-up approach have consisted of rubbed polymer 3,5,6 or photopolarized layers. 4 The problem with both of these methods is that the alignment layer is normally an electrical insulator.…”

“…Modest improvement in device performance has been achieved by increasing the conductivity of the alignment layer by the inclusion of a charge transport material. 4,5 However, such a strategy has its drawbacks in that the addition of the charge transport material can, in some cases, reduce the effective alignment of the luminescent material. 4 The second strategy for achieving polarized EL from light-emitting polymers has been to mechanically align the emissive polymer film once it has been deposited onto the electrode.…”

“…1͒ formed from a bis͑1,5-cyclooctadiene͒nickel͑0͒ catalyzed polymerization of 2,7-dibromo-9,9-di͑2-ethylhexyl͒fluorene. 5 The PF2-6 had a M w Ϸ40 000 and a polydispersityϷ2.6 ͑determined by gelpermeation chromatography against polystyrene standards͒. A PF2-6 film that had been drop cast from toluene and dried with heating overnight had a glass transition temperature of 78°C, a melting point of 135°C, and a nematic liquid crystalline phase from 135°C to over 250°C.…”