Nonconventional Liquid Crystals with a Helicene-Containing Core: Synthesis, Columnar Mesomorphism, Photoluminescence, and Electron Conductivity.

Abstract

Nonconventional mesogens featuring a [5]helicene aromatic core (i.e., 11,20-difluorotribenzo[c,k,m]naphtho[1,2-f]tetraphene, BNAn) were synthesized by two successive BuLi-assisted SNAr reactions in good yields. These tandem reactions involve an initial SNAr reaction between perfluorobenzene (C6F6) and racemic 2,2'-dibromo-1,1'-binaphthalene, followed by a second SNAr reaction with lipophilic 2,2'-dibromo-1,1'-biphenyls, respectively. These Janus-like mesogens, bearing four alkoxy chains only, exhibit exceptionally rich columnar-based mesomorphism, ranging from Colhex and Colrec to LamColrec mesophases via increasing chain-length over wide temperature ranges, extending down to room temperature. They emit light at 450 nm with a 27% quantum yield in solution, and their solid-film electron mobility reaches ca. 10-3 cm2/V s. These findings highlight the promise of these novel helicene-inspired mesogens for advanced optoelectronic thin-film devices.