Fluorenes properties

As might be anticipated from the behaviour of the parent heterocycles, C-2 of indole, benzo[i]furan and benzo[i]thiophene (Table 13) is shifted to lower field than C-3. However, the shifts for C-2 (O, 144.8 Se, 128.8 S, 126.1 NH, 124.7 Te, 120.8) and C-7a (O, 155.0 Se, 141.3 S, 139.6 NH, 135.7 Te, 133.0) in the benzo[i] heterocycles vary irregularly (80OMR(l3)3l9), and the sequence is different to that observed for C-2 in the parent heterocycles, namely 0>Se>Te>S>NH. Also noteworthy is the upheld position of C-7, especially in indole and benzofuran, relative to the other benzenoid carbons at positions 4, 5 and 6. A similar situation pertains in the dibenzo heterocycles (Table 14), where not only are C-1 and C-8 shifted upheld in carbazole and dibenzofuran relative to the corresponding carbons in dibenzothiophene and fluorene, but similar, though smaller, shifts can be discerned for C-3 and C-6 in the former compounds. These carbon atoms are of course ortho and para to the heteroatom and the shifts reflect its mesomeric properties. Little variation in the carbon-hydrogen coupling constants is observed for these dibenzo compounds with V(qh) = 158-165 and V(c,h) = 6-8 Hz. 

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. 

Charge-transfer adducts are formed with the gold(I) trimers [Au3(MeN=COR)3] (R = Me, Et), which act as electron donors, and organic electron acceptors as nitro-9-fluorenes. The structures of these adducts involve mixed stacks in which the gold trimers and the planar nitro-fluorenes are interleaved.3130 No luminescence has been observed from these solid charge-transfer adducts, which is not surprising since the luminescence of [Au3(MeN=COR)3] is a property that is associated with the supramolecular organization in the solid. 

Compounds shown in Scheme 11 are based on the fluorene system with different spacer units connecting the two benzene rings. The unit X in the 9-position strongly influences the optical properties of these alkynylgold(i) emitters. Complementary electrochemical studies have been carried out for the fluorenone species.79,80... 

In addition to 195-200, many other alkyl substituents and their derivatives have been introduced at position 9 of the fluorene nucleus in order to create a processible stable blue-emitting PF material, e.g., 203a-h [273-275,305], Chiral-substituted PFs 200 and 203g,h have been synthesized to study their chiroptical properties [306], particularly interesting due to polarized emission in such materials (see Chapter 5 in this book) (Chart 2.47). 

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... 

Copolymerization of fluorene with triarylamine compounds was shown to increase the hole-transport properties of the polymers. Several copolymers of triarylamine and fluorene (246-250) synthesized by Suzuki coupling were reported by Bradley et al. [347,348], The hole s... 

The tuning of electron injection and transport in PF has been undertaken by Shu s group [354], who introduced electron-deficient oxadiazole units as pendant groups in fluorene copolymer 257. The introduction of oxadiazole units into the PF can potentially improve the electron transport properties of the polymer, while their bulkiness can help to suppress aggregation effects (Chart 2.68). 

Efficient blue emission and good electron affinity and electron-transporting properties were demonstrated for two fluorene copolymers with dicyanobenzene moiety in the main chain, 271a,b (Scheme 2.41) [363], Due to improved electron transport properties, the device... 

A very efficient green-emitting fluorene copolymer 304 was synthesized by Shim and coworkers [390] via Suzuki coupling of dibromothieno[3,2-b]thiophene with dialkylfluorene-diboronic acid [390]. The authors compared the EL properties of this copolymer with PFO homopolymer 196 and PFO-bithiophene copolymer 295. Both the absorption and emission spectra of 304 are red-shifted compared with PFO 196 but slightly blue-shifted compared to bithiophene-based copolymer 295. PLEDs fabricated in the configuration ITO/ PEDOT/304/LiF/Al showed a pure green emission (CIE . v 0.29, r 0.63) close to the... 

SCHEME 2.47 Fluorene-phenylene vinylene copolymers and their optical and electronic properties in the solid state. 

Optical and Electronic Properties of the Fluorene-Perylene Copolymers... 

While retaining much of the substituted PT character (e.g., good hole-transport properties and stability), these materials exhibit significantly improved fluorescence efficiency in the solid state (cl>Pi up to 29%) that leads to (hllof UP to 0.1% for ITO/453/Ca PLED (Table 2.6). Other widely studied thiophene copolymers with aromatic 9,9-disubstituted fluorene units were already described above in Section 2.3. 

J. Cornil, I. Gueli, A. Dkhissi, J.C. Sancho-Garcia, E. Hennebicq, J.P. Calbert, V. Lemaur, D. Beljonne, and J.L. Bredas, Electronic and optical properties of polyfluorene and fluorene-based copolymers a quantum-chemical characterization, J. Chem. Phys., 118 6615-6623, 2003. 

Y. Fu, J. Li, S. Yan, and Z. Bo, High molecular weight dendronized poly(fluorene)s with peripheral carbazole groups synthesis, characterization, and properties, Macromolecules, 37 6395-6400, 2004. 

Q. Fang and T. Yamamoto, New alternative copolymer constituted of fluorene and triphenyla-mine units with a tunable -CHO group in the side chain. Quantitative transformation of the -CHO group to -CH=CHAr groups and optical and electrochemical properties of the polymers, Macromolecules, 37 5894-5899, 2004. 

N.C. Yang, Y.H. Park, and D.H. Suh, Synthesis and properties of new ultraviolet-blue-emissive fluorene-based aromatic polyoxadiazoles with confinement moieties, J. Polym. Sci., Part A Polym. Chem., 41 674-683, 2003. 

W. Wang, J. Xu, and Y.-H. Lai, Alternating conjugated and transannular chromophores tunable property of fluorene-paracyclophane copolymers via transannular tt-tt interaction, Org. Lett., 5 2765-2768, 2003. 

B. Liu, W.-L. Yu, Y.-H. Lai, and W. Huang, Blue-light-emitting fluorene-based polymers with tunable electronic properties, Chem. Mater., 13 1984-1991, 2001. 

M. Ranger and M. Leclerc, Optical and electrical properties of fluorene-based Tr-conjugated polymers, Can. J. Chem., 76 1571-1577, 1998. 

S.-H. Jin, M.-Y. Kim, D.-S. Koo, and Y.-I. Kim, Synthesis and properties of poly(fluorene-a/t-cyanophenylene vinylenej-based alternating copolymers for light-emitting diodes, Chem. Mater., 16 3299-3307, 2004. 

Q.D. Ling, E.T. Kang, K.G. Neoh, and W. Huang, Synthesis and nearly monochromatic photoluminescence properties of conjugated copolymers containing fluorene and rare earth complexes, Macromolecules, 36 6995-7003, 2003. 

R. Yang, R. Tian, Q. Hou, W. Yang, and Y. Cao, Synthesis and optical and electroluminescent properties of novel conjugated copolymers derived from fluorene and benzoselenadiazole, Macromolecules, 36 7453-7460, 2003. 

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