Vinylene OLEDs

Single layer OLEDs have been fabricated with a variety of emitter molecules and conjugated polymers such as poly(phenylene vinylene) (PPV). 

ErQ3 gives both PL and EL emission at 1,500 nm.207-209 Red light (614 nm) is emitted by [Eu(TTFA)3(phen)] (Figure 2(a)) doped in a poly(A-vinylcarbazole) layer.210 The complex [Eu(TTFA)3(TPPO)2] (TPPO = triphenylphosphine oxide, see Figure 2(f)) emits in the red when incorporated in OLEDs,211,212 behavior which is enhanced when the material is heat treated.204 Near-IR EL and PL emission was observed from blends of polyfp-phenylene-vinylene) with [Yb(TPP)(ACAC)] and [Er(TPP)(ACAC)] (H2TPP is 5,10,15,20-tetraphenylporphyrin) by both EL and PL 213... 

Light-emitting polymers [46,48] are a more recent development and may eventually prove superior to small-molecule OLED. Typical polymers are the green poly(para-phenylene vinylene) (PPV 53), the orange-red dialkoxy derivatives (54), and the blue polyfluorene (55) [48],... 

Enhancement in the performance of OLEDs can be achieved by balanced charge injection and charge transport. The charge transport is related to the drift mobility of charge carriers. Liu et al. [166] reported blue emission from OLED based on mixed host structure. A mixed host structure consists of two different hosts NPB and 9,10-bis(2 -naphthyl)anthracene (BNA) and one dopant 4,4 -bis(2,2-diphenylvinyl)-l,l -biphenyl (ethylhexyloxy)-l,4-phenylene vinylene (DPVBi) material. They reported significant improvement in device lifetime compared to single host OLEDs. The improvement in the lifetime was attributed to the elimination of heterojunction interface and prevention to formation of fluorescence quenchers. Luminance of 80,370 cd/m2 at 10 V and luminous efficiency of 1.8 cd/A were reported. 

The work on Alq3 and other small 7r-conjugated molecules that followed shortly thereafter13 14 demonstrated that multilayer OLEDs could be fabricated simply by thermal evaporation of these molecules. In 1990 Friend and coworkers described the first PLED,15 in which the luminescent poly(p-phenylene vinylene) (PPV)... 

Although early examples of OLEDs included polymers, specifically poly (p-phenylene vinylene) (PPV), as the emissivematerial [61 ], conjugated oligomers can also be useful emitters as well as energy harvesters. Oligomers offer advantages over their polymeric parents such as ease of synthesis and func-... 

The semi-conducting properties of conjugated polymers originate from the delocalized n orbitals formed in these carbon-containing compounds such as poly(phenylene vinylene), polythiophene and polyfparaphenylene). Like the OLED s described above, the polymer-OLED consists of a linninescent film, sandwiched between an anode and a cathode. 

As mentioned before, the incorporation of carbon nanotubes in conjugated polymers can lead to improved properties of such composites, one of them being great enhancement of the transport characteristics, which is of primary importance in organic light-emitting diodes (OLEDs) for example. Due to their solubility, which allows easy preparation, composites based on PPV (poly(phenylene vinylene)) derivatives have been extensively studied. Detailed investigation of PmPV (poly(m-phenylene... 

Conjugated polymers 189 and 190 containing a cyano group attached at a vinylene linkage have been synthesized by Knovenagel condensation [334,335]. These polymers that present reduced bandgaps of 1.75 and 1.56 eV, respectively, have been proposed for the fabrication of IR-emitting OLEDs [334]. 

Figure 6.4 Raman-spectroscopic monitoring of a polymerization reaction conducted in a microreactor to form a semiconducting polymer on basis of a polyphenylene-vinylene structure for OLED applications. The C—C double bond at 1580cm that is formed during reaction progress undergoes a strong increase in intensity that allows the determination of the macroscopic reaction rate.

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