Fluorene polymers

Some authors have suggested the use of fluorene polymers for this kind of chromatography. Fluorinated polymers have attracted attention due to their unique adsorption properties. Polytetrafluoroethylene (PTFE) is antiadhesive, thus adsorption of hydrophobic as well as hydrophilic molecules is low. Such adsorbents possess extremely low adsorption activity and nonspecific sorption towards many compounds [109 111]. Fluorene polymers as sorbents were first suggested by Hjerten [112] in 1978 and were tested by desalting and concentration of tRN A [113]. Recently Williams et al. [114] presented a new fluorocarbon sorbent (Poly F Column, Du Pont, USA) for reversed-phase HPLC of peptides and proteins. The sorbent has 20 pm in diameter particles (pore size 30 nm, specific surface area 5 m2/g) and withstands pressure of eluent up to 135 bar. There is no limitation of pH range, however, low specific area and capacity (1.1 mg tRNA/g) and relatively low limits of working pressure do not allow the use of this sorbent for preparative chromatography. 

M Bernius, M Inbasekaran, E Woo, W Wu, and L Wujkowski, Light-emitting diodes based on fluorene polymers, Thin Solid Films, 363 55-57, 2000. 

In the effort to make pure blue-emitting materials Shim and coworkers [146] synthesized a series of PPV-based copolymers containing carbazole (polymers 95 and 96) and fluorene (polymers 97 and 98) units via Wittig polycondensation. The use of trimethylsilyl substituents, instead of alkoxy groups, eliminates the electron donor influence of the latter and leads to chain distortion that bathochromically shifts the emission (Amax = 480 nm for 95 and 495 nm for 97). In addition, a very high PLQY was found for these polymers in the solid state (64 and 81%, respectively). Single-layer PLEDs fabricated with 95 and 97 (ITO/polymer/Al) showed EL efficiencies of 13 and 32 times higher than MEH-PPV, respectively (see also Ref. [147] for synthesis and PLED studies of polymers 99 and 100) (Chart 2.20). 

The first efficient phosphorescent fluorene polymer was reported by Chen et al. [83], who synthesized a series of polyfluorenes containing both the triplet-emitting iridium complex and... 

Light-emitting fluorene polymers, (VI), displaying blue electroluminescence were prepared by Mullen [6] and used in electronic devices. 

Table 2.1 Abbreviations and full names for the four poly-fluorene polymers used in this chapter. 

Fluorene polymers and copolymers (either obtained by electrochemical or chemical processes ) are proven to be among the most promising materials in the field of organic light-emitting devices (OLEDs). 

The recent synthesis of silicon-containing fluorene polymers through the carbon-silicon couphng between fluorenyl Grignard reagents and dichlorosi-lanes may also be cited [31] (cf. Scheme 12). 

A problem with blending the phosphor into a matrix is that phase separation can lead to aggregation of the phosphor, which results in low phosphorescent yields. To avoid this problem, a few researchers have incorporated iridium complexes into a polymer. A few of these structures are shown in Figure 5.19. When Jiang et al. [120] mixed polymer 19 with PBD, the PPHOLEDs had an external quantum efficiency of 3.4% and a luminance efficiency of 2.9 cd/A. Holmes [164] made a series of fluorene polymers that incorporated iridium phosphors. The most efficient PPHOLEDs had an external quantum efficiency of 1.5%, which came from triplet emission and was fabricated with 20 as the active layer. These polymers prove that incorporation of the phosphors into a polymer chain can produce efficient devices and will likely be an area of further research. The CDT Web site notes that dendimers can also be used for this purpose. Dendrons can prevent the phosphorescent core from aggregating and thus, reducing PL [165]. There is little doubt that research in the arena of electrophosphorescent displays will increase in the future. 

---