A series of highly efficient conjugated polymers have been synthesized for application in polymer light-emitting diodes (PLEDs). These polymers were based on the copolymerization between 9,9-dihexylfluorene and benzothiadiazole (BT). In several cases, a third comonomer was added to adjust the charge injecting and transporting properties of the polymers. All of these copolymers exhibited strong green emission at around 540 nm which can be attributed to either the charge transfer between an electronrich segment and an electron-deficient BT-containing segment of the polymers or the Fo ¨rster energy transfer between different polymer chains. These copolymers also exhibited very high photoluminescence quantum efficiencies up to 55%. A double-layer device using one of the copolymers as the emissive layer exhibited a low turn-on voltage (3.4 V), a very high external quantum efficiency (6.0%), and a high brightness of 59 400 cd/cm 2 .

We report new divalent osmium complexes that feature strong red metal-to-ligand-charge-transfer (MLCT) phosphorescence and electrophosphorescence. The general formula of the complexes is Os(II)(N-N)(2)L-L, where N-N is either a bipyridine or a phenanthroline and L-L is either a phosphine or an arsine. New polypyridyl ligands synthesized are 4,4'-di(biphenyl)-2,2'-bipyridine (15) and 4,4'-di(diphenyl ether)-2,2'-bipyridine (16), and the 1,10-phenanthroline derivatives synthesized are 4,7-bis(p-methoxyphenyl)-1,10-phenanthroline (17), 4,7-bis(p-bromophenyl)-1,10-phenanthroline (18), 4,7-bis(4'-phenoxybiphen-4-yl)-1,10-phenanthroline (19), and 4,7-bis(4-naphth-2-ylphenyl)-1,10-phenanthroline (20). 4,4'-Diphenyl-2,2'-bipyridine (21) and 4,7-diphenyl-1,10-phenanthroline (22) were also used in these studies. Strong pi-acid ligands used were 1,2-bis(diphenylarseno)ethane (23), cis-1,2-bis(diphenylphosphino)ethylene (24), and cis-1,2-vinylenebis(diphenylarsine) (25). Ligand 25 is used for the first time in these types of luminescent osmium complexes. These compounds feature strong MLCT absorption bands in the visible region and strong red phosphorescent emission ranging from 611 to 651 nm, with quantum efficiency up to 45% in ethanol solution at room temperature. Red organic light-emitting diodes (OLEDs) were successfully fabricated by doping the Os(II) complexes into blend of poly(N-vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD). Brightness over 1400 cd/m(2) for a double-layer device has been reached, with a turn-on voltage of 8 V. The maximum external quantum efficiency was 0.64%. Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (x, y) of the red electrophosphorescence from the complexes are (0.65, 0.34), which indicates pure red emission.

A series of cyano-containing distyrylbenzenes were synthesized as the model compounds to systematically study the effect of cyano substituents on the redox behaviors of conjugated molecules. By introducing the electron-withdrawing functional groups (cyano and dicyanovinyl) onto the phenylene ring, both electron affinity and electrochemical stability of the resulting distyrylbenzenes are greatly enhanced. The results enabled us to design and synthesize a new class of highly electron affinitive, fluorene-based copolymers with these cyano-containing chromophores as comonomers. The effects of acceptor strength and side chain on electron-transporting properties of these polymers were also investigated. By properly adjusting copolymer compositions, a combined high electron affinity and transport was achieved in a statistic copolymer, poly(fluorenebenzothiadiazole−cyanophenylenevinylene) (PFB−CNPV). An external quantum efficiency up to 0.88% and brightness as high as 4730 cd/m2 were achieved in a double-layer light-emitting diode (LED) using PFB−CNPV as the emitting layer.

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Highly efficient blue-, green-, and red-emitting polymer LEDs can be fabricated using holetransporting layers based on triarylaminescontaining perfluorocyclobutanes (PFCBs). Energy level studies suggest that ITO can inject holes into the PFCB-based materials efficiently. Moreover, the materials are rather hydrophobic, which could lead to LED devices with much better stabilities against moistureinduced degradation. The Figure The mobility of monolayer-coated gold nanowires on surfaces depends on the nature of the electrostatic interactions between the particles and the surface. Patterned surfaces (see Figure) are selectively derivatized using a mixture of attractive and repulsive interactions, and nanowire bundles are assembled in the lithographically defined wells of appropriate size.