Liquid-crystalline polymers with a bicyclo[1.1.1]pentane cage in the backbone

Nonconjugated Hydrocarbons as Rigid‐Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry

“…It has also been shown that BCP is far inferior to BCO, benzene and cyclohexane rings at stabilizing nematic phases. This is thought to be due to low rotational barriers and thus high conformational mobility of the bridgehead substituents …”

“…It has also been shown that BCP is far inferiort oB CO, benzene and cyclohexane rings at stabilizing nematic phases.T his is thought to be due to low rotational barriers and thus high conformational mobility of the bridgehead substituents. [262] BCP hasb een attached directly to the other rings such as in 207 and 208,b ut also via ester linkages such as in 206 and 209 and ethylene bonds ( Figure 28). When directly attached to an aromatic ring BCP compounds behaves imilarly to BCO analogues albeit with much lower clearingp oints.…”

“…On the other hand, when BCP is connected directly to aliphatic substituents 211 or via an ester link 209 relatively high‐phase stabilities are observed and almost exclusively in the highly‐ordered smectic phases. In order for [ n ]staffanes to exhibit liquid‐crystalline phases, a minimum of three BCP units are required, whereas with BCO only one unit is required for the nematic phase and two for the smectic phase To further cement BCP unsuitability as a LC component, a comparison between a known polymer was performed with BCP 212 , benzene and cyclohexane derivatives and as expected the BCP analogue showed strong destabilization in the smectic phases and much lower clearing temperatures …”

Molecular Rods. 1. Simple Axial Rods

“…137 Many form liquid crystals upon melting. 137,138,[144][145][146] The [n]staffane skeleton resists acids, bases, strong oxidants, and reductants (forceful reduction of hexafluorinated bicyclo[1.1.1]pentane breaks the cage 147 ). Radical abstraction of hydrogens is very difficult (chlorination 148,149 and fluorination 147 are possible).…”

“…Despite their high strain content, the parent [ n ]staffanes ( [ n ]2 ) are stable up to ∼300 °C and most derivatives are stable well above 200 °C . Many form liquid crystals upon melting. ,,− The [ n ]staffane skeleton resists acids, bases, strong oxidants, and reductants (forceful reduction of hexafluorinated bicyclo[1.1.1]pentane breaks the cage). Radical abstraction of hydrogens is very difficult (chlorination , and fluorination 147 are possible).…”