The effect of the linking group on mesogenic properties of three‐ring derivatives of p‐carborane and biphenyl

Abstract

Four series of mesogenic derivatives of p-carborane (series A[0] and A[1]) and their benzene analogues (series B[0] and B[1]) with variable linking groups were prepared and investigated for phase behaviour. The data allowed a comparison of the effect of the group on the mesophase stability as a function of the adjacent ring (carborane or benzene), the variable central ring (carborane or benzene), and the presence of an oxygen atom in the terminal chain. The results showed that substitution of carborane for a benzene ring in B[m] depresses the clearing point by 50 K to 208 K and eliminates all smectic behaviour in A[m]. The carborane derivatives A[m] are weakly dependent (effectiveness of : -CH5CHCOO-,-COO-,-CH5CH-.-CH5N-,-CH 2 CH 2 -.-CONH-), whereas the benzene analogues B[m] are strongly dependent (effectiveness of : -CONH-.-CH5CH-.-CH5N-, -CH5CHCOO-.-COO-.-CH 2 CH 2 -) on the structure of the linking group . The difference in the effectiveness of the amide group on mesophase stability (DT I 5208 K) has been attributed to the stabilizing intermolecular H-bonding in B[m], which is prevented in A[m] by steric and electronic effects of the carborane cage on the carbonyl group.

Modification of electro-optical properties of an orthoconic chiral biphenyl smectogen with its isostructural carborane analogue

“…Optimization of bulk properties is typically accomplished by structural modifications of (A)FLC compounds and the use of functionalized dopants. 5,[11][12][13] Carborane-containing liquid crystals [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] could potentially help to address these challenges in FLC and AFLC device engineering and performance. Particularly relevant in this context are the nematogenic character 19,21,[23][24][25][26][27][28][29]33 and low helical twisting power of chiral carborane mesogens.…”

Ring-alkyl connecting group effect on mesogenic properties of p-carborane derivatives and their hydrocarbon analogues

“…Therefore, it is of interest to understand how the electronic properties of the two clusters and their unusual molecular symmetry and size affect bulk properties of mesogens. Through extensive comparison of isostructural mesogenic derivatives of p -carboranes ( A and B ), bicyclo[2.2.2]octane ( C ), and benzene ( D ), we have been probing fundamental aspects of structure-property relationships in liquid crystals such as the effect of conformational properties [ 1 – 2 ], the structure of the linking group [ 5 ], and tail fluorination [ 18 – 19 ] on mesophase stability, and also the effectiveness of shielding of a lateral substituent [ 8 , 16 , 20 ] and chirality transfer phenomena [ 17 ]. Results of these studies are important for the design of new materials and optimizing of their properties for applications.…”

“…Similarly high values for phase stabilization of about 34 K are observed in pairs of alkyl and alkoxy dioxane derivatives 5[n] and 6[n] [ 4 ], as compared to similar benzene mesogens [ 24 ]. Also in series 7 – 11 the introduction of the connecting oxygen atom gives a larger increase in mesophase stability by an average of 6 ± 2 K for the 12-vertex p -carborane derivatives than for their benzene analogues [ 5 ]. However, in series 12 and 13 the effect of incorporation of the O atom as the connecting group is practically the same for all ring systems [ 15 ].…”

C(1)‐Phenethyl Derivatives of [closo‐1‐CB11H12]− and [closo‐1‐CB9H10]− Anions: Difunctional Building Blocks for Molecular Materials

“…Synthesis of the target derivatives 1 and 2 can be divided into two stages, as shown in Figure 3. The first stage involves installation of the functionalized phenethyl group at the C(1) position of anions A and B , which can be accomplished with C‐vinylation, described for the [ closo ‐1‐CB 11 H 12 ] − anion ( B ), [15b] followed by reduction of the vinyl derivative, previously demonstrated for [ closo ‐1,12‐C 2 B 10 H 12 ] derivatives [19] . Attempts at direct phenethylation of the [ closo ‐1‐CB 11 H 12 ] − anion gave poor results mainly due to elimination and formation of styrene and also difficulties with separation of the alkylation product and the unreacted anion B .…”

“…The first stage involves installation of the functionalized phenethyl group at the C(1) position of anions A and B,w hich can be accomplished with C-vinylation,d escribed for the [closo-1-CB 11 H 12 ] À anion (B), [15b] followed by reduction of the vinyl derivative, previously demonstrated for [closo-1,12-C 2 B 10 H 12 ]d erivatives. [19] Attempts at direct phenethylation of the [closo-1-CB 11 H 12 ] À anion gave poor results mainly due to elimination and formation of styrene and also difficulties with separation of the alkylation product and the unreacted anion B.T he second step involves ar egioselective electrophilic iodination with PhI(OAc) 2 ,a ccording to our general procedure [12a] and demonstrated for both anions, A and B. [12] Stage I: Installationofthe 4-substituted phenethyl group in anions A and B…”