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• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/02—Liquid crystal materials characterised by optical, electrical or physical properties of the components, in general
  • C09K19/0275—Blue phase
• • C—CHEMISTRY; METALLURGY
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  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/02—Liquid crystal materials characterised by optical, electrical or physical properties of the components, in general
  • C09K19/0225—Ferroelectric
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
  • C09K19/06—Non-steroidal liquid crystal compounds
  • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
  • C09K19/10—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings
  • C09K19/12—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings at least two benzene rings directly linked, e.g. biphenyls
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/52—Liquid crystal materials characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
  • C09K19/54—Additives having no specific mesophase characterised by their chemical composition
  • C09K19/542—Macromolecular compounds
  • C09K19/544—Macromolecular compounds as dispersing or encapsulating medium around the liquid crystal
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
  • C09K2019/0444—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit characterized by a linking chain between rings or ring systems, a bridging chain between extensive mesogenic moieties or an end chain group
  • C09K2019/0448—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit characterized by a linking chain between rings or ring systems, a bridging chain between extensive mesogenic moieties or an end chain group the end chain group being a polymerizable end group, e.g. -Sp-P or acrylate
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
  • C09K19/06—Non-steroidal liquid crystal compounds
  • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
  • C09K19/10—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings
  • C09K19/12—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings at least two benzene rings directly linked, e.g. biphenyls
  • C09K2019/121—Compounds containing phenylene-1,4-diyl (-Ph-)
  • C09K2019/123—Ph-Ph-Ph

Definitions

• the present invention relates to liquid crystal materials, and has particular but not exclusive relevance to ferroelectric liquid crystal materials.
• Such materials include ferroelectric smectic liquid crystal materials which possess a smectic C* (S c * or SmC*) phase. It will be understood by the skilled person that it is only the smectic C* phase, and not the smectic C (S c or SmC) phase, which exhibits ferroelectric properties and which has optical activity, and that a common way of obtaining a smectic C* phase is to add an optically active dopant to an ordinary smectic C liquid crystal host material or composition.
• the present invention provides a liquid crystal material comprising a smectic host component and at least one further component selected from the group consisting of
• a monomer comprising two polymerisable portions either end of an intermediate portion, or a polymer formed from said monomer; wherein the smectic host component is matched in length to the said chiral dopant or to said intermediate component.
• the smectic host component may be a single compound or may comprise a plurality of different compounds.
• the chiral dopant where present may be a single compound or may comprise a plurality of different compounds.
• the monomer may be a single compound or may comprise a plurality of different compounds, and the latter may have or may not different intermediate portions; the polymer derived therefrom may correspondingly comprise the same or different intermediate portions.
• any component is not a single compound, or when the polymer comprises different intermediate portions, properties which are a function of individual molecules, for example length and number of rings in a chain, are determined as a mole per cent weighted average.
• a smectic host component comprising equal mole amounts of two smectic compounds having 2 and 3 rings respectively will be regarded as having 2.5 rings, and the length will be the average of the lengths of the two molecules involved.
• properties, such as polarisability may be determined in a similar manner where possible, or the property of the component overall may be used.
• Length in each case is the (molecular or part molecular) length of the all-trans configuration, and is determined in the same manner, for example in each case by a computer simulation, or by the use of (physical) Drieding models. It excludes any terminal hydrogen atoms in each case, it being understood that liquid crystal and associated molecules commonly have a major long axis.
• matched in length is meant that the length of the first material referred to is within 30% of that of the second material being referred to.
• polarisability By “matched in (terms of its) polarisability” as used herein is meant that the polarisability of the first material referred to is within 30% of that of the second material. This aspect, and how it may be achieved, will be discussed in more detail later. "Polarisability” in each case may be determined in the same known manner, for example by dielectric spectroscopy o ⁇ ⁇ rom jptical measurements (birefringence/refractive index).
• polymerisable portions is meant that portion winc is necessary to the polymerisation, process.
• ⁇ for example, if the monomer is a diacrylale of the general formula (1)
• R_ is. H or lower alkyl (1 to 5 carbon atoms, preferably unbranched, and preferably methyl if not hydrogen), and A is a mesogenic core, the polymerisable portions are (2):
• both components (a) and (b) are present in addition to the smectic host. While matching in length may apply only
• the polarisability of the smectic host is also matched to the polarisability of a said other component. Where only one component (a) or (b) is present, this will then be matched for length and polarisability. Where both components (a) and (b) are present, it is particularly preferred but not necessary for the smectic host to be matched in polarisability to each of the components (a) and (b). Generally, where (a) and (b) are present and there is polarisability matching, one component is matched for length, or both length and polarisability, and the other is matched for length, or polarisability, or both length and polarisability. Both length and polarisability matching for both components (a) and (b) is most preferred.
• One particular way in which matching in length and/or polarisability can be facilitated is to choose materials with molecules of formulae having a similar appearance.
• many common smectic hosts and dopant materials comprise a chain comprising a plurality of rings which may be carbocyclic or heterocyclic, aromatic or non-aromatic. Commonly but not necessarily such rings are six membered.
• the intermediate portion of the monomer or polymer which can be used according to the invention to comprise a plurality of rings in similar manner.
• One recognised requirement for fast switching is low viscosity, and the embodiments described later are based on difluoroterphenyl host smectic C materials which as stated above are known to have remarkably low viscosities.
• the smectic host comprises a chain including a first number of rings in a chain and the dopant and/or the intermediate portion comprise a second number of rings which is within 30% of the first plurality (ring number matching).
• both components (a) and (b) are present in addition to the smectic host, while only one of such components may show such matching of ring numbers, it is particularly preferred if both components show ring matching within 30% of the smectic host.
• the rings of the first number arc preferably either all aromatic or all non- ⁇ aromatic.
• the rings of the second number as defined in the preceding paragraph are also all aromatic or all non-aromatic, and more preferably the rings of the first and second numbers taken together are cither all aromatic or all non-aromatic.
• both components (a) and (b) are present in addition to the smectic host, while either of these conditions may apply only in respect of one component, it is even more preferred if either of the conditions apply in respect of both components.
• tcrphcnyl chains arc present in all of the smectic host, all of the chiral dopant, and all of the intermediate porlion(s) of a monomer or derived polymer.
• the invention extends to a method of making a liquid crystal material, to a liquid crystal display device and to a method of making a liquid crystal display device.
• the amount of chiral dopant present in a liquid crystal material of the invention relative to (host plus dopant) is preferably no more than 30 mole per cent, more preferably no more than 20 mole per cent and even more preferably no more than 10 mole per cent. When provided, there is preferably at least 5 mole per cent of chiral dopant present.
• the present invention is not to be regarded as being limited to the types of smectic host material exemplified above. More important in many applications arc the maintenance of a S C /S ⁇ transition temperature which is not unduly altered relative to the host material, optimising the switching speed whatever the viscosity of the starting host material, and, in the case of polymer network materials, the obtaining of a system which has improved resistance to mechanical shock. Naturally, materials of lower viscosity are desirable in the context of fast display applications.
• a useful class of smectic C materials comprises a central portion consisting of a plurality of rings linked in a chain, commonly from 2 to 4 rings.
• Each of the rings may be, for example, a 5, 6 or 7 membered heterocyclic or alicyclic ring, whether aromatic or not, such as pyridine, pyrimidine, pyrrole or cyclohexane.
• the chain of rings is commonly substituted at the para position of each terminal ring, and may be further substituted on any or all of the rings in the chain.
• the invention is equally applicable to other known smectic materials, including, for example, other terphenyls, terphenyl analogues wherein one two or all of the phenyl rings is/are replaced by another 5, 6 or 7 membered heterocyclic or alicyclic ring, whether aromatic or not, such as pyridine, pyrimidine, pyrrole or cyclohexane; biphenyls and other polyphenyls, and analogues thereof as in the case of the terphenyls.
• the smectic host may be a terphenyl, e.g. a 4'4" substituted terphenyl, and more preferably a difluoroterphenyl of formula (3)
• Rl and R2 are the same or different and are each an alkyl or alkoxy group comprising from 3 to 10 carbon atoms, branched or straight chain.
• the chiral dopant may also be a te ⁇ henyl, preferably a difluorote ⁇ henyl, for example of formula (5):
• R3 and R4 are alkyl, preferably n-alkyl, having from 3 to 10 carbon atoms.
• the intermediate portion of the monomer may include a te ⁇ henyl moiety, again preferably a difluoroterphenyl moiety.
• the polymerisable portions may be acrylic ester groups.
• the monomer has the formula (6)
• A is -O- or, more preferably, -CH 2 -, and n is from 5 to 8.
• Figure 1 is a plot of apparent tilt angle as a function of temperature for five mixtures of a smectic material to which different chiral dopants have been added;
• Figure 2 is a plot of spontaneous polarisation against temperature for the same five mixtures of Figure 1;
• Figure 3 is a plot of optical response time against temperature for the same five mixtures of Figure 1;
• Figure 4 is a plot of apparent till angle as a function of temperature for three mixtures of a smectic material to which a chiral dopant has been added, two of the mixtures also comprising different polymer networks;
• Figure 5 is a plot of optical response time against temperature for the same three mixtures of Figure 4.
• Figure 6 is a plot of optical response time against temperature for three further mixtures based on a different chiral dopant
• Figure 7 illustrates the steps in the preparation of chiral dopants III and IV
• Figure 8 illustrates the steps in the preparation of chiral dopants V and VI.
• Figure 9 illustrates the steps in the preparation of chiral dopant VII.
• FIGS 10 and 11 illustrate the steps in the preparation of monomers M.l and M.2.
• S c -host The basic smectic C host used in this investigation, henceforth referred to as "S c -host", consists of a mixture of:
• Dopants HI, IV and VI contain a single chiral moiety, and were employed in a concentration of 10 mol percent of the total mixture with the S c -host, whereas Dopants V and VI have two such moieties, and provided 5 mol percent of the total mixture with the S c -host. These mixtures will henceforth be referred to as Mixtures III to VII, the numeral corresponding to the dopant employed.
• Table 1 shows the phase sequence and transition temperatures of the smectic C Host (S c -host), the Dopants HI to VII, and the ferroelectric Mixtures III to VII as determined by microscopy and differential scanning calorimetry (DSC) on heating.
• Dopant VII is a liquid at room temperature, whereas the others arc crystalline.
• Dopants IV and VI containing the -fluorooctanoic acid group also have a smectic A phase.
• Figure 1 shows the apparent tilt angle 0, measured with a low frequency rectangular wavefo ⁇ n field, typically OJ Hz, and the value extrapolated to zero field.
• Figure 2 shows the spontaneous polarisation P s as calculated from the current signals (current pulse technique) using triangular waveform fields of typically 80 to 100 Hz.
• Figure 3 shows the optical response time ⁇ , defined as the time for a 10 to 90 percent change in optical transmission with an applied rectangular wavefo ⁇ n field of 7.3 V per micron.
• the tilt angles increase with decreasing temperature.
• the values differ substantially between Dopants III and V, which both comprises the 2-hexyloxypropionic acid unit, and the Dopants IV, VI and VII which comprises an ⁇ -fluoro acid group.
• Mixtures IV and VII were investigated, each in combination with Monomer M.l or M.2.
• Mixture III exhibits a spontaneous polarisation (P of 20 nC cm “2 , a tilt angle ( ⁇ ) of 27° and an optical response time ( ⁇ ) of 95 microseconds (8 V ⁇ m "1 ) at 30 °C.
• Mixture VII shows a P s of 13.5 nC cm "2 , a tilt angle of 27.5° and a response time of 85 microseconds.
• Synthesis of Monomer M.l is given in the section labelled "Preparations”. Synthesis of Monomer M.2 is by known procedures from 2',3'-difluoro-4,4"-dihydroxy-p- te ⁇ henyl in 44 % overall yield (see Figure 8). It is considered that Monomer M.2 is better matched to the host material than Monomer M.l insofar as in Monomer M.2 the 4 and 4" positions are oxygen substituted, which inter alia is expected to affect matching of polarisability adversely.
• Compositions of Mixtures IV and VII comprised 10 mole percent of the monomer.
• the phase properties of the host S c -host, the Mixtures IV and VII (III/VII mix), the doped mixtures containing the monomer (IV/VII mix + 10%M.l/2) and the doped mixtures containing the polymer (IV/VII network 10% P.1/2) are summarised in Table 2 below.
• the monomer was polymerised in situ in an electro-optic cell as described in the Experimental Section below.
• the smectic C* to smectic A transition temperatures for the ferroelectric network systems based on the Monomer M.l are lower than those of the networks based on the Monomer M.2 and also lower than these of the original mixtures (IV/VII mix).
• the tilt angle (0) is higher and the switching times ( ⁇ ) are lower than those observed for less well matched systems (see Figures 4 and 5) and can be even lower than for the ferroelectric mixture without the polymer network ( Figure 6).
• Transition temperatures were determined by optical microscopy on heating (polarising microscope Zeiss, calibrated hot stage Mettler FP 5 with FP 52). All transitions were checked by differential scanning calorimetry (Perkin Elmer DSC 7). Electro-optic measurements: samples were investigated in 11 ⁇ m ITO test cells (EHC, antiparallel rubbed PI). Tilt angles are optical tilt angles, typical parameters are 0,1 Hz, rectangular waveform AC field (waveform generator Hewlett Packard 33120A and custom made amplifier), all values extrapolated to zero field. Response times arc optical response times taken as 10-90%) change in optical transmission using a photodiode, signal amplifier and oscilloscope (Hewlett Packard HP 54600B); typical parameters are 80 Hz, rectangular waveform AC field. Spontaneous polarisation values were measured using the current pulse technique and the above oscilloscope with computer-aided signal integration based on the IIP program 34810A bench link.
• IR Pcrkin Elmer 983G or Perkin Elmer 487G
• 'II-NMR JEOL JMN GX270 FT spectrometer (270 MHz), solvent CDC1 3
• MS Fin ⁇ igan MAT 1020 GC/MS spectrometer, solvent acetone or ether
• the purity of all target compounds was checked using TLC (silica gel F254 backed onto aluminium sheets), HPLC (Anachcm Microsorb 5 ⁇ m C 18, 25 cm/4.6 mm ID; Spectraflow 757 UV detector (254 nm); Perkin Elmer data station) and microscopy.
• Test cells were filled with the polymerisable mixtures (III/VII mix + 10%M.l/2) containing the ferroelectric system, monomer and a photoinitiator (Irgacurc 184, 5 mol% with respect to the monomer). The filling was performed in the chiral ncmatic (cholesteric) phase of the mixture in the dark. The samples were aligned using a microscope (Olympus B1I2, red light) and a hot stage (Linkam PR 600 with THM 600) for temperature control.
• the 2,3-difluorophenylboronic acid 1.7 was coupled with 4- tetrahydropyranyloxybromobenzene 2.7 according to a procedure published by M Hird et al, Liq. Cryst. 1993, 15, 123, employing tetrakis- (triphenylphosphine)palladium(O) as catalyst.
• the H-acidity at the 4-position of the resulting 2,3-difluorobiphenyl 3.7 was used to create the corresponding lithium salt at -70°C, which was then transformed into the boronic acid 4.7 in a one-pot reaction (J. Chem Soc Perkin Trans II, 1989, 2041).
• Figure 9 illustrates the preparation of dopant VII.
• 2,3-difluoro-4'-pentylbiphenyl-4- ylboronic acid 12.9 was transformed into the phenol 13.9 using a diluted hydrogen peroxide solution.
• the product was then esterified with the acid 9.8 to give dopant VII in 15% overall yield.
• Compound 23 consists of a mixture of the cis/cis, cisltrans and trans/trans isomers with an overall cis to trans ratio of ca. one to one by NMR analysis. Reaction of 23 with four equivalents of hydrogen employing palladium-on-charcoal as catalyst yielded the ⁇ ,w-diol 24, which was finally esterified with acryloyl chloride 17 to give the monomer M.l in 12 % overall yield.
• a more preferred limit in each case, taken individually (i.e. whether or not the same limit applies to the other two of these parameters) is 20% and even more preferably 10%.
• length matching between the smectic host and chiral dopant could be better than 20%, with length matching between the smectic host and intermediate portion better than 30%.
• Ring number matching could be better than 10 or 20% between the smectic host and both components (a) and (b), for example in this particular case, and possibly it could be perfectly matched, for example where all essential parts of the liquid crystal material are te ⁇ henyl derivatives.

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