Fluorene moiety

Although the exact mechanism of the fluorenone formation is not known, it is believed that the monoalkylated fluorene moieties, present as impurities in poly(dialkylfluorenes), are the sites most sensitive to oxidation. The deprotonation of rather acidic C(9)—H protons by residue on Ni(0) catalyst, routinely used in polymerization or by metal (e.g., calcium) cathode in LED devices form a very reactive anion, which can easily react with oxygen to form peroxides (Scheme 2.26) [293], The latter are unstable species and can decompose to give the fluorenone moiety. It should also be noted that the interaction of low work-function metals with films of conjugated polymers in PLED is a more complex phenomenon and the mechanisms of the quenching of PF luminescence by a calcium cathode was studied by Stoessel et al. [300],... 

Almost all modifications in PF homopolymers consist of variation of substituents at position 9 of the fluorene nucleus. Recently, Beaupre and Leclerc [303] reported a new synthetic strategy to polymers 201 and 202 with the aim to modulate the 7P of the PFs (for better injection of holes from the anode in LED) by introducing donor 3,6-dimethoxy substituents into the fluorene moiety (Scheme 2.27). The d>PL of polymer 201 is relatively low (48%), but it... 

Many studies on side-chain modifications in PF were initially based on the idea of excimer formation, resulting in the green emission during LED operation or in solid-state PL on annealing PF films. This resulted in several proposed strategies for the design of fluorene side-chain homopolymers, where bulky substituents at position 9 of the fluorene moiety should sterically prevent (hinder) interchain interaction and thus improve the stability of blue emission. 

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 2.43 Synthesis of random PFs with spiro-fluorene moieties. (From Marsitzky, D., Murray, J., Scott, J.C., and Carter, K.R., Chem. Mater., 13, 4285, 2001.)... 

Other modifications like the insertion of thiophene [80] rings, the use of fluorene moieties [81] (33), and perfluorination [62] have also been made. Compound 34 is a structural isomer to 19 with a different arrangement of the 10 rings. It has a lower tendency of crystallization than 19, but its Tg is similar (135°C). 

Steadily in the order 359, 385, 395, and 402 nm. The emission spectra exhibit a clearer vibrational fine structure than the absorption spectra. For spiro-sexiphe-nyl, 35b, a detailed analysis shows that the vibrational splitting of 0.20 eV corresponds to a phenyl breathing mode in the Raman spectrum [108]. If for spiro-sexiphenyl the outer biphenyl moieties are fixed parallel as in 4-Spiro (43), the absorption maximum is shifted from 346 to 353 nm (amorphous films) and the fluorescence maximum from 420 to 429 nm, maintaining the Stokes shift. The corresponding spectra are shown in Figure 3.17. The absorption signal at 310 nm in the spectrum of 43 can be attributed to the terminal fluorene moieties. The quantum yields for the fluorescence in the amorphous film are 38% for 35b and as high as 70 10% for 43 [89]. 

Danopoulos and co-workers reported on the preparation of NHC ligands with pendant indenyl and fluorenyl groups.19 Deprotonation of the alkyl -indene or -fluorene imidazolium salts with one equivalent of potassium hexamethyldisilazide leads to NHCs functionalised with neutral indene or fluorene moieties (IndH-NHC and F1H-NHC). Further deprotonation with... 

The synthesis of 2-monosubstituted or 2,2 -disubstituted precursor compounds can be achieved by two different routes direct electrophilic aromatic substitution or the use of substituted derivatives of 9-fluorenone. hi many cases, the first route is complicated due to the fact that the two fluorene moieties in spirobifluorene react chemically independently of each other. The formation of products monosubstituted in the 2-position is therefore often accompanied by the formation of byproducts (Fig. 6). A good example is the nitration of spirobifluorene, which was investigated by Weisburger and coworkers [23]. They discovered that a careful control of reaction times and conditions allowed for the formation of 2-nitro-9,9 -spirobifluorene or 2,2 -dinitro-9,9 -spirobifluorene as the main product. Especially in the case of 2-nitro-9,9 -spirobifluorene, however, the conversions are low because the reaction must be quenched before a suitable amoimt of the dinitro compound is formed. 

In contrast to thiophene-5,5 -dioxide, the non-aromatic character of which limits the stability of the derived materials, the aromatic dibenzothiophene-5,5 -dioxide is very stable and topologically equivalent to a fluorene moiety. Its LUMO energy level is 1 eV Iowct than that in fluorene [168], and several highly fluorescent molecular and oligomeric materials based on dibenzothiophene-5, 5 -dioxide have been synthesized and studied (125 and 126). Diphenylamino end-capped dibenzothiophene-5,5-dioxide derivatives 125a-c were used as emitters [73a, 169, 170], the dibenzothiophene-5,5-dioxide-quinoxaline derivative 126 was used as an electron-transporting material [171], and multilayer OLEDs based on these compounds demonstrated excellent performance (Table 19.5). 

Fluorinated PAEs with Anthracene and Fluorene Moieties... 

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