Thermotropic and Lyotropic Liquid Crystalline Phases of Rigid Aromatic Amphiphiles

Abstract

Rodlike amphiphilic molecules that contain exclusively aromatic building-blocks and no flexible alkyl chains have been synthesized and their mesomorphic properties investigated. These novel compounds bear diol head groups of different size (2,3-dihydroxypropyloxy or 5,6-dihydroxy-3-oxahexyloxy groups) at one end of a biphenyl unit, various aromatic segments (benzyloxy, 4-, 3-, or 2-methylbenzyloxy, phenoxy groups) at the other, and additional methyl substituents in different positions. They were synthesized by using Suzuki cross-coupling reactions as the key steps. Their thermotropic mesomorphism was investigated by means of polarized light optical microscopy, differential scanning calorimetry, and, for enantiotropic phases, by X-ray scattering. The liquid crystallinity of this class of compounds is influenced by protic solvents, such as water and glycerol. Dependent on the temperature and the solvent content, different SA phases were found. Several mesophases resulting from the frustration of these layer structures (e.g., different columnar phases, optical isotropic mesophases, and nematic phases) were also present. The smectic phases have different degrees of intercalation (SAd, SA2). The columnar phases are supposed to be ribbon structures that result from the collapse of the smectic layers. They occur in some pure compounds or they are induced upon the addition of protic solvents. The particular phase sequences of the different compounds depend mainly on the position of the methyl substituents at the biphenyl cores and are largely determined by the degree of intercalation of the aromatic cores.

Dendritic Domains with Hexagonal Symmetry Formed by X‐Shaped Bolapolyphiles in Lipid Membranes

“…Compounds B n ( n =12,18) with glycerol groups were obtained in a similar way to that used previously for structurally related compounds. [29] Herein, 1,2- O -isopropylidene glycerol substituted phenylacetylene ( 2 )[31] was coupled in a Sonogashira reaction[32] with 4-bromotrimethylsilylethinylbenzene ( 1 a )[33] to obtain 4′-1,2- O -isopropylideneglycerol-functionalized 4-ethinyltolane 4 a after basic cleavage (K 2 CO 3 /MeOH) of the C-terminal trimethylsilyl group. [34] Sonogashira coupling of 4 a (2 equiv) with 2,5-dibromohydroquinone ethers 5 ( n =12, 18)[35] led to compounds 6 a ( n =12, 18), which were deprotected with Py ⋅ TsOH in methanol[36] to give the BPs B12 and B18 , respectively.…”

Thermotropic liquid crystalline drugs

“…or substitutes such as halides, nitro-or cyano-groups (Demus & Zaschke 1984;Neubert 2001b). Rod-like amphiphilic mesogens that contain exclusively aromatic building blocks and no flexible alkyl chains have also recently been synthesized (Kolbel et al 2000).…”

Effects of Lateral and Terminal Chains of X-Shaped Bolapolyphiles with Oligo(phenylene ethynylene) Cores on Self-Assembly Behaviour. Part 1: Transition between Amphiphilic and Polyphilic Self-Assembly in the Bulk

“…The synthesis of all other bolapolyphiles C-E was conducted via series of repetitive Sonogashira cross-coupling reactions [82] and required protection/deprotection procedures, as shown in Schemes 3 and 4. The synthesis of the glycerol terminated compounds C-E (x = 0, Scheme 3) starts with 4-bromo(2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy)benzene (1) [83], which is coupled with trimethylsilylacetylene to yield compound 2 [84]. After K2CO3 catalyzed desilylation [85], the obtained 4-ethynyl(2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy)benzene (3) [43] was coupled with 4-bromo(trimetylsilylethynyl)benzene (4-Br) [86] to yield the 4′-(2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy) substituted 4-etynyltolane 6 after desilylation [43].…”

“…After K2CO3 catalyzed desilylation [85], the obtained 4-ethynyl(2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy)benzene (3) [43] was coupled with 4-bromo(trimetylsilylethynyl)benzene (4-Br) [86] to yield the 4′-(2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy) substituted 4-etynyltolane 6 after desilylation [43]. Two equivalents of 6 were coupled with the appropriately functionalized 2,5-dibromo-or 2,5-diiodohydroquinone ethers 7 [87,88], giving the bolapolyphiles C-E after deprotection of the 1,2-diol groups with pyridinium p- The synthesis of the glycerol terminated compounds C-E (x = 0, Scheme 3) starts with 4-bromo (2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy)benzene (1) [83], which is coupled with trimethylsilylacetylene to yield compound 2 [84]. After K 2 CO 3 catalyzed desilylation [85], the obtained 4-ethynyl(2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy)benzene (3) [43] was coupled with 4-bromo(trimetylsilylethynyl)benzene (4-Br) [86] to yield the 4 -(2,3-O-isopropylidene-2,3-dihydroxypropyl-1-oxy) substituted 4-etynyltolane 6 after desilylation [43].…”