Liquid crystalline polyfluorenes

M. Grell, W. Knoll, D. Lupo, A. Miesel, T. Miteva, D. Neher, H.-G. Nothofer, U. Scherf, and A. Yasuda, Blue polarized electroluminescence from a liquid crystalline polyfluorene, Adv. Mater., 11 671-675, 1999. 

M. Grell, D.D.C. Bradley, G. Ungar, J. Hill, and K.S. Whitehead, Interplay of physical structure and photophysics for a liquid crystalline polyfluorene, Macromolecules, 32 5810-5817, 1999. 

M.J. Banach, R.H. Friend, and H. Sirringhaus, Influence of the casting solvent on the thermotropic alignment of thin liquid crystalline polyfluorene copolymer films, Macromolecules, 37 6079-6085, 2004. 

HG Nothofer, A Meisel, T Miteva, D Neher, M Forster, M Oda, G Lieser, D Sainova, A Yasuda, D Lupo, W Knoll, and U Scherf, Liquid crystalline polyfluorenes for blue polarized electroluminescence, Macromol. Symp., 154 139-148, 2000. 

Low polarisation ratios (<2 1) for absorption had also been found for amorphous PPV (1) deposited from solution by spin-coating on rubbed poly(tetrafluoroethylene) [PTFE]. It is evident that this could be improved on by making use of the high order parameter and self-organising properties of the nematic phase of liquid crystalline electroluminescent polymers such as those (16, 28 and 78-82) shown in Table 6.16. - 2 ° This was then found subsequently to be the case using thermotropic liquid crystalline polyfluorenes, such as 28 and 80 shown in Table 6.6 and segmented PPV derivatives, such as 81. The nematic phase exhibits the lowest viscosity of... 

Grell, M., et al. 1999. Blue polarized electroluminescence from a liquid crystalline polyfluorene. Adv Mater 11 671. 

Redecker, M., Bradley, D.D.C., Inbasekaran, M., Woo, E.P. Mobility enhancement through homogeneous nematic alignment of a liquid-crystalline polyfluorene. Appl. Phys. Lett. 74, 1400-1402 (1999)... 

D. Neher, Polyfluorene homopolymers conjugated liquid-crystalline polymers for bright emission and polarized elecroluminescence, Macromol. Rapid Commun., 22 1365-1385,2001. 

M Oda, HG Nothofer, G Lieser, U Scherf, SCJ Meskers, and D Neher, Circularly polarized electroluminescence from liquid-crystalline chiral polyfluorenes, Adv. Mater., 12 362-365, 2000. 

One effect of aryl substituents on the physical properties of polyfluorenes is to inhibit chain packing as demonstrated by the lack of liquid crystalline... 

In this context, polyfluorenes (PFs) and polyfluorene-based materials have received considerable attention, especially because of their intense blue photo- and electroluminescence but also for their liquid crystalline properties [4-8]. Although improvements concerning color purity and device stability of polyfluorene-based PLEDs have recently been made, the strict requirements for commercialization, demanding tens of thousands of hours of operation, are still unreached goals for blue fight-emitting PLEDs. 

In the above study it could be shown that the relaxation of triplets in conjugated polymers is in quantitative agreement with predictions based on the concept of random walk in a disordered solid. Meanwhile, this theoretical framework for the description of migration of triplets in disordered solids has been applied to PFO (polyfluorene with octyl side chains) [168] as well. PFO contains liquid crystalline domains in the polymer that leads to the formation of highly ordered domains (fi phase). This ft phase plays an essential role in the photophysics of this polymer, notably on triplet migration. 

Soluble polyfluorenes were found to give a liquid crystalline behaviour. For example, poly(9,9-di(ethylhexyl)fluorene (PDF2/6) (Figure 5.14) was found to have a transition into a birefringent fluid phase [145] which can he obtained in a highly oriented arrangement by... 

Neher, D. 2001. Polyfluorene homopolymers Conjugated liquid-crystalline polymers for bright blue emission and polarized electroluminescence. Macromol Rapid Commun 22 (17) 1366-1385. 

Many synthetic routes are utilized to generate 6,12-functionalized dihydroindeno[l,2-h]fluorenes, typically from 22 or 26. One direct method is base-promoted alkylation of the methylene carbons of 26. For example, lithiation of 26 followed by treatment with 1-bromooctane gave tetrasubstituted 101 (Scheme 29) [80]. Subsequent bromination at the 2- and 8-positions with CuBr/ alumina furnished 102, which could then be polymerized to form polyindeno-fluorene 103 linked at the 2- and 8-positions rather than at the 6- and 12-positions as seen in Scherf s polyindenofluorene 85. Muellen and co-workers foxmd that 103 showed a bathochromic shift in fluorescence compared to polyfluorene (into the visible region) and it formed a liquid crystalline phase at high temperature, possibly making a suitable LED component. 

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