Polyfluorenes homopolymers

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

Neher, D. 2001. Polyfluorene homopolymers Conjugated hquid-crystalline polymers for bright blue emission and polarized electroluminescence. Macromol Rapid Common 22 1366. 

Neher D (2001) Polyfluorene homopolymers Conjugated liquid-crystalline polymers for bright blue emission and polarized electroluminescence, Macromol Rapid Cornmun 22 1365-1385. Scherf U and List E (2002) Semiconducting polyfluorenes - towards reliable structure-property relationships, Adv Mater 14 477-487. 

The described synthesis of polyfluoren homopolymers allows also the design of alternating copolymers. Instead of the 2,7-dibromofluorene a variety of dibromoarenes ean be used in the Pd-catalyzed coupling polymerization reaction. An important group of... 

Recently, the synthesis of polymer nanocomposite OLEDs based on a new series of sulfide-containing polyfluorene homopolymers and copolymers and CdSe/ZnS nanocrystals was described by Yang et al. [38]. CdSe/ZnS nanoparticles were grafted to sulfur atoms by a ligand-exchanging reaction. The EL efficiency of nanocomposite OLEDs was effectively improved by QD nanocrystals incorporated in the polymers [38]. 

As the archetypical blue emitting polymer, polyfluorene has been studied extensively using a wealth of optical techniques to elucidate its photophysical properties. Moreover, as it is a simple homopolymer that can be synthesized to very high purity, it offers a unique platform to help us understand many aspects of the excited state behavior of conjugated polymers in general. Here we address the main properties associated with excited state, i.e. exciton, behavior and the many possible interactions between excitons that can occur, although this is by no means an exhaustive review. 

Polyfluorenes are an important class of LEP with high thermal, photo and environmental stability and efficient bright blue emission. This stimulated a number of researchers to develop fluorene-thiophene copolymers for light-emitting applications. In addition to an expected increase in PL quantum etSciency, such a combination of electron-rich thiophene units with relatively electron-deficient fluorene units should modify the bandgap of the material (and thus tune the emission) and improve the charge injection/transport balance, compared with fluorene homopolymers. 

Three principal types of Suzuki polymerizations for polyfluorenes have been developed for homopolymers and copolymers by Dow, Cambridge Display Technology (CDT), and Covion, which was merged with Merck. Early detailed experimental procedures were reported in the patent literature (Scheme 5.5 and Table 5.2). These and other groups have used these polymerizations for numerous poly fluorene derivatives (Table 5.3). 

Chain-growth catalyst-transfer polycondensation (CTP) is a rapidly developing polymerization method, as it allows, in many cases, the above-mentioned limitations of step-growth polymerizations to be overcome. CTP provides a straightforward access to well-defined conjugated homopolymers (e.g., polythiophenes (1), polyfluorenes (2), polyphenylenes (3), etc.), alternate donor-acceptor copolymer e.g., 4) and all-conjugated block polymers (e.g., 5), Chart 20.1. 

The MEM analysis of time-resolved fluorescence decays of several copolymers is shown in Fig. 15.18a. For the homopolymer PF2/6, only a narrow distribution is observed around 360 ps. However, for copolymers PF/FLx, with different fractions of fluorenone residues, distributed randomly along the polymer chain, the distribution at 360 ps is accompanied by two additional peaks. These are observed around 20 and 100 ps as a result of quenching of polyfluorene emission, due to energy transfer from the fluorene to the fluorenone sinks. Figure 15.18b shows the fluorescence decay of the copolymer labelled with 25 % of fluorenone groups, analysed with a sum of three exponential functions. Note the good agreement between MEM and multiexponential analysis [91]. 

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