Oligophenylene

Rehahn et al. [35] recently presented the synthesis of constitutionally homogeneous oligophenylenes, 22a/b, with 2,5-alkyl substituents located on the central aromatic ring, generated via the cross-coupling reaction of Suzuki. They are exclusively linked in the para-positions and composed of 3 -15 benzene rings. 

More recently, Mullen et al., have worked out very efficient methods for generating highly arylated, branched oligophenylene- and related oligoarylene derivatives, following different synthetic procedures based on polyaddition reactions in the key step. 

This modular methology involves the repetition of directed protection/cyclo-addition/deprotection steps, and allows for the synthesis of monodisperse dendritic oligophenylenes of the first (46a, 22 benzene rings) and second (46b, 62 benzene rings) generation [60]. Within the synthetic sequence, the authors made use of the different reactivities of protected and deprotected ethynylene functions within the key cycloadditon step. 

Staab et al. showed that the intramolecular coupling of terminally halogena-ted meta-linked oligophenylenes can afford cyclic structures, as shown here for the cyclization of the dibromo-sexi(meta-phenylene) derivative, 49, to the cyclic meta-phenylene hexamer, 50 [62]. 

Keywords Dendrimers, linear aliphatic molecules, oligophenylenes, repetitive synthesis, supramolecular chemistry. 

Fig. 14. Iterative convergent-divergent preparation of oligophenylenes according to Tour et al.

Table 1 Values of the decay factor, / , for aliphatic and oligophenylene chains obtained with different experimental systems...

It has been reported that the electrical properties of single molecules incorporating redox groups (e.g. viologens [114, 119, 120, 123, 124], oligophenylene ethynylenes [122, 123], porphyrins [111, 126], oligo-anilines and thiophenes [116, 127], metal transition complexes [118,128-132], carotenes [133], ferrocenes [134,135],perylene tetracarboxylic bisimide [93, 136, 137] and redox-active proteins [138-143]), can be switched electrochemically. Such experiments, typically performed by STM on redox-active molecules tethered via Au-S bonds between a gold substrate and a tip under potential control, allow the possibility to examine directly the correlation between redox state and the conductance of individual molecules. 

Fig. 6 Schematic representation of an Hg-drop LAJ incorporating SAMs of organic molecules of (a) alkanethiols, (b) oligophenylene thiols and (c) benzylic derivatives of oligophenylene thiols of different length formed on an Ag electrode, (d) Semi-logarithmic plot of measured current at applied bias I 0.5 V vs electrode gap flowing through the a, b, c interfaces...

The decrease in thickness of the monolayer upon chemical flattening of the molecules can be shown by STM. The importance of the defined graphitic structures suggests the transfer of this novel strategy, namely the surface-induced PAH synthesis, to considerably larger oligophenylene precursors. 

Copolymer 459, prepared by Stille coupling of dibromophenylene with 2,5-Mv(tributyl-stannyl)thiophene, represents another example of a phenylene-u/t-thiophene backbone, where the substituted phenylene unit forms an oligophenylene vinylene fragment that is not in the main conjugation chain [561]. A PLED fabricated with this polymer (ITO/459/A1) emitted green light (520 nm) with a turn-on voltage of ca. 9.5 V, but no other data on luminance or efficiency of the device were reported (Chart 2.111). 

Later, Kallitsis and coworkers reported similar PPP copolymers, with oligophenylene blocks separated by nonconjugated aliphatic chains. Copolymers 496 [595], 497 and 498 [596] contained the oligophenylene blocks in a main chain or as pendant substituents,... 

B. Jiang, S.-W. Yang, and W.E. Jones, Jr., Conjugated porphyrin polymers control of chromo-phore separation by oligophenylene vinylene bridges, Chem. Mater., 9 2031-2034, 1997. 

A perfluorinated, para-conjugated oligophenylene with high EA exhibited improved electron transport properties and was investigated as an ETM (100-103) (Scheme 3.32) [155]. The electron mobility of NPF-6 (100), determined by the TOF technique, is much higher than that... 

T. Gu, D. Tsamouras, C. Melzer, V. Krasnikov, P. Gisselbrecht, M. Gross, G. Hadziioannou, J.-F. Nierengarten, Photovoltaic devices from fullerene oligophenylene ethynylene conjugates, Chem Phys Chem, vol. 3, pp. 124-127, 2002. 

We planarized the appropriate oligophenylene derivative via oxidative intramolecular cyclodehydrogenation, which has been introduced by Kovacic and... 

Rhodium-catalyzed alkyne cyclotrimerization is also applicable to the synthesis of a polyalkyne substrate bearing ether-linked 1,6-diyne moieties 59, which is easily prepared by Pd-Cu-catalyzed Sonogashira couphng reactions. These reactions provide a novel and efficient synthetic route to oligophenylene 60, which bears benzodihydrofur-an moieties (Scheme 7.17) [40]. 

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