Biphenyl core

In this way, Miillen and co-workers have, c.g., generated 43 starting from a 3,3, 5,5 -tetraethynylsubstituled biphenyl core and 44 [64]. 

An interesting variant of fully atomistic simulations arises when rigid sections of the model mesogen are replaced by simpler potentials. Cross and Fung [111] have replaced the biphenyl core of some n-alkylcyanobiphenyls with a large... 

The IR dichroism measurements allowed a fairly precise determination of the preferential molecular conformations both in the smectic Ai and X phases (see Sect. 2.3). In the smectic Ai phase the biphenyl moiety is parallel on average to the layer normal, while the hydrocarbon and perfluorinated fragments are tilted at angles 18 and 32°, respectively. The phase transition to the smectic X phase is accompanied by a dramatic change in the main molecular conformation - now all the fragments are strongly tilted with respect to the layer normal (especially the biphenyl core which tilts at an angle of around 56°) (Fig. 12). 

In line with a second novel synthetic principle, the authors further developed the repetitive Diels-Alder procedure, in which monomers containing cyclopentadienone (dienophile) units were reacted with protected/deprotected ethynylene functions (see [31]). In this way, they generated a novel class of highly arylated phenylene dendrimers 46, starting from a 3,3, 5,5 -tetraethynyl-substituted biphenyl core [60]. 

Figure 8.5 Thermal properties of gold complexes with isocyanides having a phenyl or a biphenyl core.

Figure 8.6 Proposed explanation for the different influence of a biphenyl core on the melting and the clearing points.

Switching from the biphenyl core to a 3-phenylpyridine core resulted in compounds that were similar in potency to the biphenyl compounds, but with increased inhibition of ACC2 versus ACC1, as... 

The biphenyl core 9 promotes the growth of the dendrimer from the 3,3, 5,5 positions. The aforementioned tetraphenylmethane core 4 allows a tetrahedral growth of the dendrimer, whereas the 1,3,5-triethynylbenzene core 10 and the hexa-(4-ethynylphenyl)benzene core 11 promote an anisotropic extension along the plane of the central phenylene ring, so that propeller and pancake-shaped dendrimers should be obtained (Scheme 4). From all these cores it is possible to synthesize dendrimers up to the fourth generation, the properties of which will be presented later. 

The fourfold cycloaddition of an excess of cyclopentadienone dendron 27 to the tetraethynyltetraphenylmethane 4 in diphenylether at 200°C affords dendri-mer 2 in 85% isolated yield, respectively (see Scheme 7). Dendrimer 2 corresponds to the second-generation polyphenylene dendrimer made by the divergent method [30]. It should be mentioned that while the addition of dendron 27 to the biphenyl core 9 takes two days the addition to the tetraphenylcore 4 takes one week. This can be explained by the higher mobiUty of the biphenylic core compared to the stiff tetrahedral core, which allows the proper orientation of the ethynyl functions for reactions with the bulky dendrons. 

This stiffness also has an influence on the shape of the dendrimers, when different core building units are employed. The biphenyl core 9 leads to the dumbbell shaped molecule whose most stable conformers show a twist between 20° and 60° around the central biphenyl unit. 2, based on the tetrahedral core 4, with a diabolo-like molecular shape which resembles the shape of the core very well. Due to the large number of benzene rings around the central methane unit, the branches are hindered in their rotation (Scheme 4), lowering the internal mobility of the molecule compared to 15. 

Scheme 9. Three-dimensional stick-and-ball model of the first four generations of a polyphenylene dendrimer built from the biphenyl core and the A2B building blocks...

We have decorated different generations of polyphenylene dendrimers based on a biphenyl core with up to 16 perylenemonoimide chromophores at the periphery [67]. This has been achieved via the Diels-Alder reaction of a perylenemonoimide functionalized cyclopentadienone as a terminating reagent with the ethynyl precursor dendrimers. A strongly emitting nanoparticle is thus obtained. 

Scheme 19. Second generation polyphenylene dendrimer based on a biphenyl core decorated with 8 perylenemonoimide dyes... 

Research utilizing the thiepine skeleton in material science has been reported. For example, liquid crystals with chiral dihydrodibenzo[c,i ]thiepines were studied. The enantiomerically pure (-)-(i )-3,9-bis[4-(dodecyloxy)benzoyl-oxy]-5,7-dihydro-l,l l-dimethyldibenzoR,f]thiepine 80 and (—)-(R)-3,9-bis[4-(dodecyloxy)benzoyloxy]-5,7-dihydro-1,1 l-dimethyldibenzoR,f]thiepine dioxide 82 display smectic C mesophases by a rigid twisted biphenyl core and axial chirality <1998JOC3895>. 

Tour et al. [13e] also replaced the phenyl or the biphenyl core of OPEs with one or two pyridine moieties. The aim was to lower the LUMO energy and hereby to produce a better match with the Fermi level of the metal contact and higher current through the device. An example is shown in Scheme 10.14. After desilyla-tion, 45 was subjected to a two-fold cross-coupling with 1 to provide 46. 

In a very recent publication Thomas and coworkers used the same principle with a custom-synthesized mesogen (LC) based on an imidazole head-group and a rigid biphenyl core with, however, a ten- and eight-carbon... 

We also expected the stability of the phenylnaphthyl core is better than that of the biphenyl core since it has more resonance structure and higher radical stability. Three EL devices ITO/2-TNATA/HTM 2/EML/Alq3/LiF/Al (device IV), ITO/2-TNATA/HTM S/EML/Alqa/LiF/Al (device V), and ITO/2-TNATA/HTM 4/EML/Alq3/LiF/Al (device VI), were fabricated in order to estimate their suitabilities as a hole transporting material in comparison with the reference device ITO/2-TNATA/HTM l/EML/Alqs/LiF/Al (device... 

Fig. 6.14 Packing of molecular dimers in the nematic (a), smectic A (b) and reentrant nematic (c) phases. The middle part of dimers formed by rigid biphenyl cores is broader than their end parts formed by molecular tails and the length of the dimers depends on the pressure and temperature...

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