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Synthesis and Liquid Crystalline Self‐Assembly of Concave Diindoles with a Hydropentalene Core
Author(s) -
Bühlmeyer Andrea,
Ehni Philipp,
Ullmann Dustin,
Frey Wolfgang,
Baro Angelika,
Laschat Sabine
Publication year - 2021
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.202001656
Subject(s) - mesogen , mesophase , alkoxy group , chemistry , biphenyl , liquid crystal , crystallography , stereochemistry , side chain , phase (matter) , organic chemistry , liquid crystalline , materials science , alkyl , optoelectronics , polymer
Fischer indole reaction of Weiss diketone with 4‐bromophenylhydrazine provided the 2,8‐dibromo‐hexahydropentaleno[2,1‐ b :5,4‐ b’ ]diindole key intermediate, which was converted to the target compounds by N ‐protection/Suzuki cross‐coupling. Variation of protecting groups, mesogenic units, and their alkoxy substitution gave calamitic diindole mesogens. Both N ‐protection and alkoxy chain influenced the mesomorphic properties of phenyl diindoles. Among the differently N ‐protected derivatives only ethylcarbamate‐protected ones formed enantiotropic mesophases. Mesophase range and type were controlled by the chain lengths: chains≤C12 gave nematic (N) phases, diindoles with side chains≥C14 formed additional lower temperature smectic (SmA) phases. Irrespective of the chain lengths 4′‐alkyloxybiphenyl diindoles formed N and SmA phases upon first heating but tended to decomposition below their clearing points. X‐ray crystal structure analysis of bis(4′‐decyloxy)biphenyl diindole reveals that in the solid‐state the folding angle of the hydropentalene core caused an almost perpendicular orientation of the two indole/biphenyl parts with respect to each other.