PF Copolymers

Copolymerization of fluorene with other highly luminescent materials offers a possibility of fine-tuning the emitting and charge-transport properties of PF. Thus Miller and coworkers 

SCHEME 2.37 Synthesis of anthracene-fluorene copolymers. (From Klarner, G., Davey, M.H., Chen, E.-D., Scott, J.C., and Miller, R.D., Adv. Mater., 13, 993, 1998.) 

a random copolymer 242a,b with slightly different substituent pattern was synthesized by Stephan and Vial [341] by polymerization with Zn/NiCl2 (see Appendix). Both 

FIGURE 2.20 Schematic illustration of a disorder in polyfluorene introduced by carbazole-3,6-diyl unit in the main chain. (From Xia, C. and Advincula, R.C., Macromolecules, 34, 5854, 2001. With permission.) 

Leclerc s group [345,346] in Canada first synthesized PF copolymer 245 based on carbazole-2, 7-diyl units that, in contrast to the above examples, is a fully conjugated system. Just as in carbazole-3,6-diyl copolymers, polymer 245 showed absorption and PL spectra similar to those of PFO 196, with almost the same PL QE. However, there was no sign of the green emission band in this copolymer after thermal annealing (Chart 2.63). 

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The highly branched dendronized PF copolymers are readily soluble in common organic solvents. All the three-generation copolymers showed high molecular weights of Mn ... 

Shim and coworkers [320] synthesized cross-linked PF copolymers, containing siloxane bridges 221 and 222. Ni-mediated copolymerization of 9,9-dihexyl-2,7-dibromofluorene in... 

Many other PF copolymers, which do not contain a particularly electron-active moiety, but nevertheless, can improve the performance of the material in PLED have been synthesized. The Huang group [364,365] at Institute of Materials Research and Engineering (IMRE, Singapore) synthesized deep-blue copolymer 272 by Suzuki copolymerization of fluorene-diboronic acid with dibromobenzene. The emission band of 272 has a peak at 420 nm and a well-defined vibronic feature at 448 nm with a fwhm of 69 nm, and virtually no green emission,... 

An unusual synthetic approach to PF copolymers was demonstrated by Bunz and coworkers [370], who prepared poly(fluorene ethynylene) 281a-e by metathesis polymerization reaction (Scheme 2.44) [370], The aggregation of polymers 281 in concentrated solutions and in solid state is manifested in slight (up to 10-20 nm) red shift of the absorbance and emission peaks, although solutions and films emit pure blue light. 

Miller s group [415-417] at IBM reported two series of statistical PF copolymers using perylene and cyano-substituted phenylene vinylene chromophoric segments (Scheme 2.51). 

It is recommended that a reslurry of crude OSL in an organic solvent or 10% aqueous salt (e.g., NaHCOa) solution be performed to remove low-molecular-weight (mono-functional) species, waxes, and carbohydrates. This purification leads to an improvement in OSL reactivity and contributes to the usefulness of OSL as a PF resin extender or PF copolymer raw material. It is presumed that extraneous removed materials in the crude lignin react with formaldehyde but do not lead to productive cross-linking polymer formation. 

A further development of the approach of using multicomponent PF copolymers for tuning the emission color was recently exemplified by fabrication of fan RGB (red/green/blue color specification) prototype display, in which the pure red, green, and blue colors was achieved by variation of the feed ratio of several monomers (03NAT(421)829). 

Another PF copolymer 28, composed of alternating DOF and thieno-[3,2-b]thiophene, was reported by Iim et al. [59]. The incorporation of electron-rich thieno- [ 3,2- b ] thiophene moiety in the polymer backbone led to lower HOMO (5.38 eV) and higher LUMO (2.4 eV) levels than those of PFO (HOMO 5.8 eV, LUMO 2.12 eV [12]). The device ITO/PEDOT PSS/28/IiF/Al exhibited a pure green emission with a peak at 515 nm and CIE coordinates of (0.29, 0.63), which is very close to the standard green required by the National Television System Committee (NTSC) (0.26, 0.65). In addition, the maximum brightness and efficiency of this device were 970 cdm 2 and 0.32 cd A-1, respectively. 

Dow Chemical Company presented a series of PF copolymers, consisting of various charge-transport moieties and low band-gap chromophores on the backbone, for tuning the emission color of PLED to cover the whole visible range [63]. They claimed that their blue-, green-, and red-emitting copolymers (without disclosing chemical structures and ratios of comonomers) can exhibit acceptable device performance, as shown in Table 1. 

In the solid state, see Fig. 15, the emission of PFS copolymers also appears dependent on the S content. For high S percentages, the emission appears... 

Single molecule experiments on PF copolymers containing different amounts of fluorenone units (see Fig. 10a) represent the most convincing experimental way to prove the monomolecular origin of the green emission [26]. 

C. Binders from PF Copolymers with Other Resins... 

Fig. 15 Tapping mode AFM images of 30 nm thin PI-6-PFS copolymer films of different compositions A PI volume fraction of 0.72, B PI fraction of 0.76, C PI fraction of 0.80. Each scan size is 1 xm. Reprinted with permission from [81]. Copyright 2000, American Chemical Society...

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