Fluorene-based molecules

Recently, another pathway was used to synthesize indolo [ 3,2-ft ] carbazole-based molecules containing aromatic substituents on both ends of the material. First, octyl side chains are added on the nitrogen atoms then, aromatic substituents can be added by using either Suzuki or Stille cross-coupling starting with 2,8- or 3,9-dibromo-5,ll-dioctylindolo[3.2-b]carbazoles. As shown in Scheme 11, the addition of phenyl, thiophene, biphenylamino-phenyl, fluorene, and even carbazole units has recently been reported in the literature [20,93]. 

The photochemical stabihty of the molecules is characterized by the quantum yield of photodecomposition, (P = N/Q [69], where N and Q are the numbers of decomposed molecifles and absorbed photons, respectively. The photochemical properties of the fluorene derivatives were investigated in different organic solvents (hexane, CH2CI2, ACN, and polyTHF) at room temperature by the absorption and fluorescence methods and comprehensively described [70-72]. These methods are based on measurements of the temporal changes in the steady-state absorption and fluorescence spectra during irradiation. For the absorption method, the quantum yield of the photodecomposition under one-photon excitation, c >ipa, can be obtained by the equation [73] ... 

The protecting group is removed using a base. This works because of the acidity of the proton in position 9 on the fluorene ring. Removal of that proton causes a breakup of the molecule with the release of the amine at the end. 

The relatively strong Bronsted acidity of cyclopentadienes, indenes, and fluorenes, permits the formation of alkali metal compounds of the conjugate bases of these organic molecules by direct reaction with the metal. The effect of substitnents on the rate of formation of 9-R-fluorenylhthium componnds in THE solution and on the degree of ion pairing in solutions of these species has been determined. Potassinm derivatives are commonly prepared by the reaction of the cyclopentadiene with potassium bis(trimethylsilyl)amide. Eluorenyl and indenyl compounds with the heavier alkah metals, Rb and Cs, are also prepared by reaction with the metal bis(trimethylsilyl)amide. The cyclopentadienyl ring in alkali metal compounds can also be coordinated to other metals. ... 

Belfield et al. studied different dipolar molecules based on fluorene derivatives for the TT-system with a diphenylamine and a benzothiazole as the electron donor and acceptor, respectively (Fig. 6). 

The implication here is that diphenylmethane and triphenylmethane are not able, because of their nonplanarity, to form a sodium addition compound. Neither are they acidic enough to react directly with sodium in a displacement reaction at the moderate temperatures employed. They are, however, acidic enough to react with the disproportionated form of the sodium addition compound of naphthalene, which is a much stronger base than sodium itself. Fluorene, because of its planarity, is able to form the addition compound, which then is able to act as a base toward two other fluorene molecules. 

Fig. 4.2 The structure of an X trap. Here, we show a dibenzo-thiophene molecule (Fig. 1.2) in a fluorene single-crystal host (Fig. 1.1). The scheme shows the orientation of the dibenzo-thiophene molecules (arrows with circle) due to the increased space taken up by the sulphur atom in the dibenzo-thiophene molecule. The fluorene molecules nearest to the dibenzo-thiophene (arrows, dashed) are rotated about 2.5 degrees out of their equilibrium positions in the pure crystal. After [3], based on ENDOR measurements.

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