A Combined Directed Metalation Cross-Coupling Route to a New Smectic Liquid Crystal With a Phenanthrene Core

Abstract

A series of phenanthrene and oxidized phenanthrene derivatives with typical substitution patterns, 1.31, 1.32, 2.30a-f, 3.1a,b and (-)-4.1 have been synthesized as liquid crystal cores by a combined Directed ortho Metalation (DoM), cross coupling and Directed Remote Metalation (DreM) strategy. The synthetic methodology employed allowed variation of the tail and core structures, for the preparation of a new smectic liquid crystal compound (1.32), a homologous series of 9,10-dihydrophenanthrene-9,10-diones (2.30a-f), a diastereomeric trans-9,10-dihydrophenanthrene-9,10-diol (1.31), two enantiomeric 9,10-dihydrophenanthrene-9,10-diones (R)-3.1a-b) and an enantiomeric 9,10-dihydro-9,10-dimethylphenanthrene-9,10-diol ((-)-4.1). Polarized microscopic and differential scanning calorimetric measurements suggest that 1.31 forms a large range of SmC phase, ca. 100 ºC, followed by a small range of nematic phase, ca. 10 ºC; the 2.30a-f series show similar mesogenic properties, but with the extension of the length of a side chain from six carbons to eleven carbons, the nematic phase has disappeared (in the cases of 2.30a-c). Although (R)-3.1a-b and (-)-4.1 are not liquid crystals, they show ferroelectric induction by doping, in the amount of ca. 5 mol%, into unchiral liquid crystal hosts PhB, DFT, PhP1, NCB76 and 2.30f. However, due to the detection limit of the instrument, i.e., ca. 0.5 nC/cm2, the spontaneous polarizations (Ps) induced could not be measured.