Patent DE-19934799-A1 (DE)
Title: Active matrix display with high contrast, e.g. for notebook PC's, contains a chiral-smectic liquid mixture of compounds with linked aromatic or heteroaromatic rings and special compounds with mesogenic groups
Inventor: DUEBAL HANS-ROLF
IPC: C09K19/40
Filed: 1999-07-28
Abstract: A chiral-smectic liquid crystal mixture for active matrix displays contains compound(s) with 2 linked (hetero)aromatic rings and/or compound(s) with 3 linked (hetero)aromatic rings and 0.1-50 wt% special mesogenic compounds with 1-3 (hetero)aromatic or alicyclic rings linked by single bonds or by ester, alkylene or oxymethylene groups.  Active matrix displays containing a chiral-smectic liquid crystal (LC) mixture with the phase sequence I-N asterisk -SmC asterisk , a spontaneous polarisation of less than 40 nC/cm<2> in the working temperature range and a pitch of more than 10 microns at at least one temperature in the nematic or cholesteric phase. The LC mixture contains at least one compound of at least two of the types of formula (A), (B) and (C), plus 0.1-50 wt% compound(s) of formula (D) in which  R<1>-R<6>  = H or 2-18C alk(en)yl (with or without asymmetric carbons and optionally with 1 or 2 non-adjacent CH2 groups replaced by -O- and/or with one CH2 replaced by -C equivalent to C- or -Si(CH3)2- and/or with one or more H replaced by F, and with no adjacent heteroatoms), with the proviso that only one of the groups R<1>/R<2> or R<3>/R<4> or R<5>/R<6> may be hydrogen;  Y<1>-Y<6>  = -O-, -OCO-, -COO-, -OCOO- or a single bond;  Z<1>  = -OCO- or -COO-; A, B  = 1,4-phenylene (optionally substituted with up to 3 F atoms), or pyrimidine-, pyridine- or pyridazine-2,5-diyl (all optionally with one F substituent), with the proviso that one of the rings A, B must be one of the above nitrogen heterocycles;  C, D, E  = 1,4-phenylene (optionally F-substituted as above), with the proviso that at least one of these rings is fluoro-1,4-phenylene or ortho-difluoro-1,4-phenylene;  F, G, K  = as for A and B and with the same proviso;  R<20>, R<21>  = (a) 2-12C alkyl, alkenyl, alkoxy or alkenyloxy (optionally with 1 or 2 non-adjacent CH2 replaced by -OCO-, -COO-, -Si(CH3)2- or cyclopropane-1,2-diyl and optionally with one or more H replaced by F), or (b) a group with at least one asymmetric C atom, which is either part of a 3-16C alkyl group, in which 1-4 non-adjacent CH2 may be replaced by -O-, -OCO- or -COO- and one of the substituents on the asymmetric C must be CH3, CF3, OCH3, Cl, F, CN or OCF3, or part of a 3- to 7-membered carbocycle in which 1 or 2 non-adjacent CH2 may be replaced by -O- or one CH2 may be replaced by -OCO- or -COO-, with the proviso that a group of type (b) is in at least one of the groups R<20> and R<21>, and M<18> or M<19> is a single bond if the group with the asymmetric C is an alkyl group;  A<14>-A<17>  = 1,4- or 1,3-phenylene (both optionally substituted with 1 or 2 F or Cl), 1,4-cyclohexylene (optionally with one F or CN), cyclohex-1-ene-1,4-diyl or its 1-fluoro derivative, cyclohex-2-ene-1,4-diyl, 2-oxocyclohexane-1,4-diyl, 2-cyclohexen-1-one-3,6-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo(2.2.2)octane-1,4-diyl, spiro(4.5)decane-2,8-diyl, spiro(5.5)undecane-3,9-diyl, indane-2,5-diyl, naphthalene-2,6-diyl (optionally with 1 or 2 F or CN groups), pyrimidine-, pyridine- or pyrazine-2,5-diyl (all optionally with one F), pyridazine-3,6-diyl, quinoline-2,6- or -3,7-diyl, isoquinoline-3,7-diyl, quinazoline- or quinoxaline-2,6-diyl, 1,3-dioxan-2,5-diyl, thiophen-2,4- or -2,5-diyl, 1,3-thiazole-2,5- or -2,4-diyl, isoxazole-3,5-diyl, benzothiazole-2,6-diyl (optionally with one or more F), 1,3,4-thiadiazole-2,5-diyl, piperidine-1,4-diyl or piperazine-1,4-diyl;  M<14>-M<17>  = -OCO-O-COO-, -OCH2-, -CH2O-, -CH2CH2-, -(CH2)4-, -C equivalent to C- or a single bond;  M<18>, M<19>  = -OCO-, -COO-, -OCH2-, -CH2O- or a single bond;  a, b, c, d = 0 or 1;  (a+b+c+d)  = 1-3;  (A asterisk -M asterisk )  = a single bond if the corresponding index is zero . An Independent claim is also included for LC mixtures as defined above.