Core units aromatic

Core7-Rpt4-Periph7. In these, the value of shifted from 588 mV for n = 1 to 785 mV for n = 3 (versus Ag/AgCl, 100 mM BU4NPF6 in benzonitrile, GCE). The aromatic ester repeat unit and solvent are unique to this investigation and may be important considerations in addition to the environmental sensitivity of this core unit. 

The first dendrimers with chiral cores for studies on the influence of the stereo-genic centres of a core unit on the chiroptical properties of the overall molecule were presented by Seebach s group [18]. These workers first synthesised dendrimers based on a chiral tris(hydroxymethyl)methane core unit. To these were attached zeroth- to second-generation Frechet dendrons, either directly or separated from the core by an aliphatic (n-propyl) or an aromatic spacer (p-xylylene) (Fig. 4.62). Remarkably, the dendrimers with aliphatic spacer showed no significant optical activity. This loss of chiral information was attributed to a dilution effecf, resulting from linkage of the achiral dendron to the chiral core unit,... 

Fig. 4.62 Chiral-core dendrimers of various generations (according to Seebach et al.), consisting of a chiral tris(hydroxymethyl) methane core unit and poly (aryl ether) dendrons (GO, Gl, or G2), which are linked to the core either directly (A), via an aliphatic spacer (B), or via an aromatic spacer (C)...

Organic compounds containing pyrimidine as a core unit were known to exhibit various biological and pharmaceutical activities [108], Chun et al. [109, 110] developed a one-pot synthesis of a series of 5-aiyl-5,8-dihydrotetrazolo[l,5-a]py-rimidine-7-carboxylic acids 72 from 5-aminotetrazole, pymvic acid, and aromatic aldehydes in the presence of I2 as a catalyst. Operational simplicity, mild reaction conditions, and eco-friendly procedure made this novel protocol a promising alternative for the fusion of tetrazolopyrimidines (Scheme 10.54),... 

The cyclohexane ring in phenyl cyclo-hexanecarboxylates and in the PCH compounds, 2.5, usually enhances nematic character relative to that of the aromatic systems and even greater enhancement is achieved with cyclohexyl cyclohexanecarboxylates or a bicyclohexyl core unit such as 2.6. The esters are prepared as outlined in Scheme 6 and the bicyclohexyl systems are obtained by the route shown in Scheme 2 a similar reduction of the aromatic ring to that shown in Scheme 6 and equilibration with thionyl chloride to give the trans-acid [28, 29] allows the terminal cyano compound to be obtained. 

Figure 5.7 Structures of small molecules with DPP core and aromatic end-cap units that have enabled the fabrication of SM-BHJ solar cells with PCE greater than 4%.

Thus such polar units in the torninal chains are best avoided in the genontion of nematic matoials, unless other structural features are included to disrupt tiie lamellar attractions (e.g. lateral substituents). The use of an all loxy tominal chain with liquid crystals (compounds 33) based on aromatic core units tends to gena ate higho phase stability than compounds with analogous alkyl chains (compounds 9). 

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