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Macrocyclic Effects in the Mesomorphic Properties of Liquid‐Crystalline Pillar[5]‐ and Pillar[6]arenes
Author(s) -
Nierengarten Iwona,
Guerra Sebastiano,
Holler Michel,
KarmazinBrelot Lydia,
Barberá Joaquín,
Deschenaux Robert,
Nierengarten JeanFrançois
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201300356
Subject(s) - mesophase , chemistry , pillar , paraformaldehyde , crystallography , polarized light microscopy , liquid crystal , differential scanning calorimetry , molecule , optical microscope , polymer chemistry , stereochemistry , organic chemistry , scanning electron microscope , materials science , physics , optoelectronics , structural engineering , optics , engineering , composite material , thermodynamics , phase (matter)
Whereas the reaction of 1,4‐bis(2‐bromoethyloxy)benzene ( 4 ) with paraformaldehyde in the presence of BF 3 · Et 2 O afforded exclusively the cyclopentameric pillar[5]arene derivative ( 5 ), both cyclopenta‐ and cyclohexameric macrocycles 5 and 6 were obtained when the reaction of 4 with paraformaldehyde was performed at 45 °C in CHCl 3 with FeCl 3 as the catalyst. Treatment of compounds 4 – 6 with sodium azide provided the corresponding polyazides, to which a cyanobiphenyl building block was subsequently grafted to generate model compound 1 , pillar[5]arene 2 , and pillar[6]arene 3 , bearing two, ten and twelve mesomorphic subunits, respectively. The liquid‐crystalline and thermal properties of the compounds were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). Comparison of the liquid‐crystalline properties of macrocycles 2 and 3 with those of 1 revealed the strong influence of the macrocyclic pillar[ n ]arene core on the mesomorphic properties. Whereas only a monotropic mesophase was observed for 1 , a broad enantiotropic mesophase was evidenced for both pillar[ n ]arene derivatives.