End-capped polyfluorenes

Miller and coworkers [325] reported using an anthracene end capper (which is twisted orthogonally in respect to the neighboring fluorene moiety) in PF 227 to enhance the color stability of PLEDs. However, the results show that the PLED fabricated with the anthracene 

SCHEME 2.35 Synthesis of dihexyl-PF end capped with 2-fluorenyl groups. (From Klaerner, G. and Miller, R.D., Macromolecules, 31, 2007, 1998 Lee, J.-I., Klaerner, G., and Miller, R.D., Chem. Mater., 11, 1083, 1999.) 

FIGURE 2.18 The efficiency-luminance plot for ITO/PEDOT/228/Ca device. The numbers along the curve are the CIE coordinates at the corresponding brightness levels. The insert shows the EL emission spectrum of a diode driven at 3.6 V. (From Miteva, T., Meisel, A., Knoll, W., Nothofer, H.G., Scherf, U., Muller, D.C., Meerholz, K., Yasuda, A., and Neher, D., Adv. Mater., 13, 565, 2001. With permission.) 

Styrene-containing polymer is completely soluble in common solvents such as CHCI3, THF, xylene, or chlorobenzene and can be spin cast as thin films that are easily cross-linked 

Some other PFs end capped with cross-linkable groups, such as benzocyclobutene, have been patented by Dow Chemicals [275-277]. For example, the thermal curing of spin-coated polymer 232 gave an insoluble pinhole-free film without alteration of the fluorescent properties (Chart 2.57). 

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Scheme 6 Synthesis of end-capped polyfluorene by AB-type Suzuki polycoupling...

Hsu et al. [75,76] reported a new method for incorporating metal complexes into polyfluorenes to prepare phosphorescent polymers (polymer 47 and 48). A pyridine end-capped polyfluorene has been synthesized. The pyridine was used to form a polymer metal complex with 2,2-bipyridyl(tri-carbonyl)rhenium(I) chloride. Using the end-capping approach not only can control the molecular weight of polymer, but also avoid the interference of the metal complex and conjugated polymer in energy transfer. They can... 

Scheme 14 Synthesis of end-capped polyfluorenes with on-chain Re(I) complexes...

A. E. Javier, S. R. Varshney, R. D. McCullough, Chain-Growth Synthesis of Polyfluorenes with Low Polydispersities, Block Copolymers of Fluorene, and End-Capped Polyfluorenes Toward New Optoelectronic Materials. Macromolecules 2010,43,3233-3237. 

The doubly end-capped polyfluorenes 216 and 217, with phenol or carboxylic acid functional groups at the chain termini, have been made by addition of 13 mol % of suitable end-capping reagents to the Yamamoto polymerisation of a dibromofluorene followed by conversion of the protected functionalities (Scheme 98) [315]. The materials appeared to be totally end-capped by NMR analysis. 

Scheme 98 Synthesis of doubly end-capped polyfluorenes as units for rod-coil copolymers...

Javier AE, Varshney SR, McCullough RD. Chain-giowth synthesis of polyfluorenes with low polydispersities, block copolymers of fluorene, and end-capped polyfluorenes toward new optoelectronic materials. Macromolecules 2010 43 3233-3237. 

T. Miteva, A. Meisel, W. Knoll, H.G. Nothofer, U. Scherf, D.C. Muller, K. Meerholz, A. Yasuda, and D. Neher, Improving the performance of polyfluorene-based organic light-emitting diodes via end-capping, Adv. Mater., 13 565-570, 2001. 

Miteva, T., et al. 2001. Improving the performance of polyfluorene-based organic light-emitting diodes via end-capping. Adv Mater 13 565. 

Scheme 51 Preparation of a polyfluorene end-capped with a cross-linkable group...

Scheme 66 Polyfluorenes end-capped with hole-transporting groups...

The results indicated that all polyfluorene chains are successfully end-capped at least at one end while only a small fraction of polythiophene chains is end-capped. 

Rhenium(I) tricarbonyl-2,2 -bipyridine moieties were used to cap both ends of a poly fluorine, yielding Re-capped Re(bpy)(CO)3(py)-X-(py)(CO)3(bpy)Re 2+ polymers, where X = polyfluorene [51, 52], The polymers with and without the Re caps were spin-coated from their solutions in CH2C12 onto an ITO surface previously modified with a layer of poly(styrene sulfonic acid), doped with poly(ethylenedioxythiophene). The LED (light-emitting device) was then topped with a layer of Ca/Al. The photoluminescence (PL) and electroluminescence seen were consistent with the presence of [Re(bpy)(CO)3(py)]+ [158],... 

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