| abstract |
New 2-fluoro-, 2-chloro-, 2-difluoromethoxy, 2-trifluoromethyl- and 2-trifluoromethoxy- 1,3,4-tri- or -1,3,4,5-tetrafluorobenzene cpds. are of formula (I): where n = 0-7; Q = -O-, -CH=CH- or a single bond; r = 0-5; s = 0-2; X = F, Cl, OCHF2, CF3 or OCF3; L = H or F; A = 1,4-cyclohex-1-enylene, 1-hydroxy-1,4-cyclohexylene, Z, Z-Ar, Ar-Z or Z-Cyc; Z = a single bond, -(CH2)2- or -(CH2)4-; Ar = 1,4-phenylene or biphenyl-4,4'-diyl; Cyc = trans-1,4-cyclohexylene. More specifically in specified types of (I): X = F; and : (Ia) n = 1, Q = -O-, r= 2-5 and s = 1 or 2; (Ib) n = 1-7, Q = a single bond, r = O and s = 1 or 2; pref. s = 2, A = Z and esp. Z = a single bond or (CH2)2- or s = 1 and A = Ar; (Ic) n = 1-7 and A = 1-hydroxy-1,4-cyclohexylene; (Id) n = 1-7 and A = 1,4-cyclohex-1-enylene; (Ie) n = 1-7, s = 2 and A = -C2H-; or (If) n = 1-7, s = 1 and A = -C2H4-Cyc-. USE/ADVANTAGE - (I) are claimed for use as components of liquid crystal (LC) media for electrooptical displays and the LC medium and displays are also claimed. They are esp. useful in nemtatic media with positive dielectric anisotropy and have a wide nematic range, nematogenicity down to low temps., excellent chemical stability and elastic properties, little temp. dependence of the threshold voltage and/or small optical anisotropy. They are also readily soluble in the other components of the medium and have high positive dielectric anisotropy and favourable viscosity. They give STN displays with very steep electrooptical characteristics and active matrix displays with excellent long-term stability. In addn., pure (I) are colourless and form LC mesophases in a favourable temp. range. |