Rubrene synthesis

The synthesis of a tetraphenyl derivative (rubrene, Expt 6.13) of the linearly fused tetracyclic aromatic hydrocarbon naphthacene involves an interesting intermolecular cyclisation process between two molecules of 1-chloro-1,3,3-triphenylpropa-1,2-diene. This substituted allene is formed in situ from 1,1,3-triphenylprop-2-yn-l-ol (Expt 5.41) when the latter is allowed to react with thionyl chloride and the resulting chlorosulphite ester heated with a little quinoline cyclisation occurs spontaneously under these reaction conditions to give rubrene which has an intense red colour. 

Heymann et al. [255] and Smith et al. [256] reported the synthesis of C70O 82 by photooxygenation. Irradiation of an oxygenated toluene solution of C70 and rubrene as a sensitizer resulted in the formation of a nearly 1 1 mixture of two C70O isomers 82a and 82b that can not be separated (Fig. 31). The structures of 82a and 82b were elucidated by UV-vis spectroscopy, 13C-NMR studies as well as 3He NMR studies. No evidence for the formation of isomers 82c and 82d was found. 

The PL quantum yield r)pl. While r]pl of many dyes is close to 100% in solution, in almost all cases that yields drops precipitously as the concentration of the dye increases. This well-known concentration quenching effect is due to the creation of nonradiative decay paths in concentrated solutions and in solid-state. These include nonradiative torsional quenching of the SE,148 fission of SEs to TEs in the case of rubrene (see Sec. 1.2 above), or dissociation of SEs to charge transfer excitons (CTEs), i.e., intermolecular polaron pairs, in most of the luminescent polymers and many small molecular films,20 24 29 32 or other nonradiative quenching of SEs by polarons or trapped charges.25,29 31 32 In view of these numerous nonradiative decay paths, the synthesis of films in which r]PL exceeds 20%, such as in some PPVs,149 exceeds 30%, as in some films of m-LPPP,85 and may be as high as 60%, as in diphenyl substituted polyacetylenes,95 96 is impressive. 

Synthesis of substituted rubrene has been reported through the cycloaddition of substituted isobenzofuran and naphthyne generated in situ (Scheme 16.27) [30]. Dehydration leading to aromati-zation of the Diels-Alder adduct was initiated by AlBrj as the Lewis acid in the presence of Csl. 

Dufraisse, C. and Horclois, R., Synthesis of naphthacenes with the characteristics of rubrenes. Bull. 

Aubry, J. M., Rigaudy, J., and Cuong, N. K., A water soluble rubrene derivative synthesis, properties and Oj trapping, Photochem. Photohiol, 33, 149, 1981. 

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