Fluorene, 9,9-disubstituted

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. 

Esters of ethenetetracarboxylic acid, (37), and disubstituted (fluoren-9-ylidene)me-thane derivatives, (38), are reduced sequentially to radical anions and dianions [2, 68, 84, 85]. Only the dianions are sufficiently basic to be useful as EGBs [53,86]. For (37), the two reduction potentials are separated by 0.2 V [68], and even with a working potential allowing formation only of the radical anion, the dianion can be formed by disproportionation. The protonated form of the dianionic EGBs, (37H) and (38H) , will normally be stable in solution since the pK values of the dihydro products are expected to be in the range 12 to 16. 

The Ir-catalyzed [2+2+2] cycloaddihon of diynes and monoalkyne advocates a new synthehc approach to silafluorenes [13]. The Ir-PPh3-complex-catalyzed reac-hon of benzene and silicon-tethered 1,6-diynes with disubstituted alkynes gave tetra-subshtuted silafluorenes (Scheme 11.3). The consecutive [2+2+2] cycloaddihon of two types of tehayne provided a ladder-type silafluorene and a spirosilabi-fluorene (Schemes 11.4 and 11.5). 

Exciton coupling between the two styryl chromophores in each of the conformers (A)-(C) leads to a negative Cotton effect at around 270 nm, as shown by theoretical analysis using the 71-electron SCF Cl dipole velocity MO method. Therefore, the tram-2,.1-disubstituted spirocyclo-propane-1,9 -fluorene derivative 6, from which the distyryl derivative was obtained, must have accordingly the 2S3S absolute configuration122. 

Onychine (135) was first described as a natural product in 1976, when its isolation from Onychopetalum amazonicum (Annonaceae) was reported (83), and its structure was given as 4-methyl-l-azafluoren-9-one (158) on the basis of elemental analysis and high-resolution MS, as well as UV, IR, and H-NMR spectra. As in all the azafluorenone alkaloids discovered to date, the complex UV spectrum is reminiscent of that of fluoren-9-one, and the H-NMR spectrum clearly indicates the presence of a 2,3-disubstituted 4-methylpyridine moiety. The immediate conclusion, therefore, is that onychine is either l-methyl-4-azafluoren-9-one (135) or 4-methyl-l-azafluoren-9-one (158), which is supported by the spectral properties of the secondary alcohol obtained by reduction of the ketone group and of the acetylation and hydrogenolysis products of this... 

Esters of ethenetetracarboxylic acid (6) and disubstituted-(fluoren-9-ylidene)methane derivatives (7) are reduced sequentially to radical anions and dianions. It is the dianions that display useful basicity on a preparative scale (discussed later). 

Good yields of substitution products can be obtained if elimination is precluded. Alkyllithium addition to fluorenone tosylhydrazone (120) provides access to 9,9-disubstituted fluorenes (121 equation 18). ... 

Hydride abstraction of 1-(cycloprop-2-enyl)indenes and 9-(cycloprop-2-enyl)fluorenes 15 (obtainable by the reactions of 1,2-disubstituted cyciopropenylium ions and the indenyl or fluorenyl anion) with the tritylium cation, followed by treatment with tertiary amines, is one of the earliest calicene syntheses affording 1,2-benzocalicenes and 1,2 3,4-dibenzocalicenes 16. ... 

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. 

Polyfluorenes with alkyl substituents at C9 are soluble in conventional organic solvents such as aromatic hydrocarbons, chlorinated hydrocarbons and tetrahydrofuran, which made them useful to prepare thin films for OLEDs. As a consequence many efforts have been undertaken to synthesize a large number of high-molecular-weight, 9-mono-, or disubstituted very pure fluorene-based polymers. 

Rault-Berthelot J, Angely L, Delaunay J, Simonet J (1987) The polyfluorenes a family of versatile electroactive polymers. (11) Poly(9,9-disubstituted fluorenes) existence of reversible p or n doping. New J Chem 11 487 94... 

Hapiot P, Lagrost C, Le Floch F, Raoult E, Rault-Berthelot J (2005) Comparative smdy of the oxidation of fluorene and 9,9-disubstituted fluorenes and their related 2,7 -dimers and trimer. Chem Mater 17 2003-2012... 

Wang, Y.-H., Bailey, J.F., Petersen, J.L. and Wang, K.K. (2011) Synthesis of 5-(2-methoxy-l-naphthyl)- and 5-[2-(methoxymethyl)-l-naphthyl]-llH-benzo[f)]fluorene as 2,2 -disubstituted l,l -binaphthyls via benzannulated enyne-allenes. Beilstein Journal of Organic Chemistry, 7, 496-502. 

---