Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/004—Optical devices or arrangements for the control of light using movable or deformable optical elements based on a displacement or a deformation of a fluid
  • G02B26/005—Optical devices or arrangements for the control of light using movable or deformable optical elements based on a displacement or a deformation of a fluid based on electrowetting
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B1/00—Dyes with anthracene nucleus not condensed with any other ring
  • C09B1/005—Di-anthraquinonyl and derivative compounds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B13/00—Oxyketone dyes
  • C09B13/02—Oxyketone dyes of the naphthalene series, e.g. naphthazarin
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B23/00—Methine or polymethine dyes, e.g. cyanine dyes
  • C09B23/10—The polymethine chain containing an even number of >CH- groups
  • C09B23/105—The polymethine chain containing an even number of >CH- groups two >CH- groups
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B29/00—Monoazo dyes prepared by diazotising and coupling
  • C09B29/0003—Monoazo dyes prepared by diazotising and coupling from diazotized anilines
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B33/00—Disazo and polyazo dyes of the types A->K<-B, A->B->K<-C, or the like, prepared by diazotising and coupling
  • C09B33/02—Disazo dyes
  • C09B33/12—Disazo dyes in which the coupling component is a heterocyclic compound
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B33/00—Disazo and polyazo dyes of the types A->K<-B, A->B->K<-C, or the like, prepared by diazotising and coupling
  • C09B33/02—Disazo dyes
  • C09B33/16—Disazo dyes from other coupling components
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B33/00—Disazo and polyazo dyes of the types A->K<-B, A->B->K<-C, or the like, prepared by diazotising and coupling
  • C09B33/18—Trisazo or higher polyazo dyes
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B33/00—Disazo and polyazo dyes of the types A->K<-B, A->B->K<-C, or the like, prepared by diazotising and coupling
  • C09B33/18—Trisazo or higher polyazo dyes
  • C09B33/24—Trisazo dyes of the type
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B43/00—Preparation of azo dyes from other azo compounds
  • C09B43/32—Preparation of azo dyes from other azo compounds by reacting carboxylic or sulfonic groups, or derivatives thereof, with amines; by reacting keto-groups with amines
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B55/00—Azomethine dyes
  • C09B55/005—Disazomethine dyes
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B55/00—Azomethine dyes
  • C09B55/005—Disazomethine dyes
  • C09B55/006—Disazomethine dyes containing at least one heteroring
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B57/00—Other synthetic dyes of known constitution
  • C09B57/007—Squaraine dyes
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
  • C09B57/00—Other synthetic dyes of known constitution
  • C09B57/02—Coumarine dyes

Definitions

• Electro wetting display devices are known. In an off state of such a display device an oil covers the area of a pixel of the display. In an on state the oil is retracted so as not to cover the pixel area. To switch the pixel into the on state a voltage is applied across the oil via an electrically conductive fluid immiscible with the oil, which exerts an electrostatic force on the conductive fluid, and to switch the pixel into the off state the voltage is switched off.
• the oil is coloured
• a radiation beam passing through the pixel when in the off state passes through the oil and is imparted with colour, but does not pass through the oil with the pixel in the on state, and so its colour remains substantially unchanged.
• Backflow is where, despite the voltage being switched on and continuously applied, the oil tends to flow back from the on state to eventually adopt the off state. Due to backflow, disadvantageously, a desired optical effect which would be provided in a radiation beam by the oil in the on state is not maintained. Instead, an undesired optical effect corresponding to the oil being in the off state, or in an intermediate state between the on and off states is provided.
• FIG. 1 shows a schematic cross-section of part of an example of a known display device
• FIGS. 2a, 2b and 2c show schematically compounds in accordance with embodiments; and [0007] FIG. 3 shows schematically a synthesis method of a compound according to an embodiment.
• the present invention relates to electrowetting apparatus, particularly, but not exclusively, to a dye for a fluid of electrowetting apparatus.
• electrowetting apparatus including a compound comprising a plurality of colorant moieties and a linker, the plurality of colorant moieties including a first colorant moiety having a first net dipole and a second colorant moiety having a second net dipole, wherein the plurality of colorant moieties are linked by and disposed around the linker so that the first net dipole and the second net dipole at least partially cancel each other.
• a compound comprising a plurality of colorant moieties and a linker, the plurality of colorant moieties including a first colorant moiety having a first net dipole and a second colorant moiety having a second net dipole, wherein the plurality of colorant moieties are linked by and disposed around the linker so that the first net dipole and the second net dipole at least partially cancel each other.
• FIG. 1 shows a schematic cross-section of part of a known example of a display device 1.
• the display device is an example of electrowetting apparatus and includes a plurality of electrowetting elements 2, one of which is shown in the FIG.. The lateral extent of the element is indicated in the FIG. by the two dashed lines 3, 4.
• the electrowetting elements comprise a first support plate 5 and a second support plate 6.
• the support plates may be separate parts of each electrowetting element, but the support plates may be in common for the plurality of electrowetting elements.
• the support plates may be made for instance of glass or polymer and may be rigid or flexible.
• the display device has a viewing side 7 on which an image formed by the display device can be viewed and a rear side 8.
• the first support plate faces the viewing side; the second support plate faces the rear side.
• the image is formed by light passing through each electrowettmg element from the rear side 8 to the viewing side 7, where it is transmitted through the first support plate 5.
• the element may include a reflector for reflecting light, entering the element from the viewing side 7 back through the viewing side 7.
• Such a reflective element may alternatively be constructed with a second liquid 11 described below, the electrode 14, the hydrophobic layer 13 and the walls 16 adjacent the first support plate 5.
• the image is built up of picture elements. Each picture element may contain a single electrowettmg element.
• each picture element may contain a plurality of electrowettmg elements, each electrowettmg element forming a sub-picture element.
• the latter picture element may for example include three sub-picture elements provided with colour filters for red, green and blue, thereby forming an RGB picture element.
• An illumination unit 9 may be attached to the rear side 8 of the plurality of electrowettmg elements to provide backlighting of the electrowettmg elements.
• the illumination unit may comprise a single white light source. It may also comprise a plurality of colour light sources e.g. for spectrum sequential operation of the display. The colours of the light sources may for example be yellow and blue.
• the light sources may be conventional light sources, such as fluorescent lamps or LEDs.
• the illumination unit may be of a conventional construction, such as disclosed for instance in international patent application WO 2006/011101.
• a space 10 between the support plates is filled with a first fluid and a further, second fluid, for instance a first liquid 12 and a second liquid 11 respectively.
• the first liquid is immiscible with the second liquid.
• the second liquid is electrically conductive or polar, and may be a water or salt solution such as a solution of potassium chloride (KC1) in a mixture of water and ethyl alcohol.
• the second liquid may be transparent.
• the first liquid is electrically non-conductive and may for instance be an alkane like decane or hexadecane, silicone oil, or decaline (otherwise known as bicyclo-4,4.0-decane).
• a hydrophobic layer 13 is arranged on the electrode 14, facing the space 10.
• the layer may be an uninterrupted layer extending over a plurality of electrowettmg elements or it may cover only the cross-section of one electrowettmg element.
• the layer may be for instance an amorphous fluoropolymer layer such as AF1600 or other low surface energy polymers such as Parylene.
• the hydrophobic character causes the first liquid to adhere preferentially to the support plate 6.
• Each electro wetting cell includes an electrode 14 arranged on the support plate 6.
• the electrode is separated from the liquids by an insulator which may be the hydrophobic layer 13.
• the electrode has the same shape as the cross-section of the electrowetting element, but in other embodiments the electrode may have a different shape than the cross-section of the electrowetting element.
• a second electrode 15 is connected to the conductive second liquid 11. This electrode can be common to a series of electrowetting cells that share the second liquid, uninterrupted by walls.
• the electrodes on the support plate 6 are connected to an electrical terminal on the support plate by a matrix of printed wiring.
• the electrodes 14 are preferably transparent and made of e.g. indium tin oxide or reflecting (e.g. aluminium).
• the matrix may include switching elements such as transistors; in this case the matrix is called an active matrix.
• the apparatus comprises at least one electrode arranged relative to the fluids such that applying an electrical potential to the at least one electrode changes a configuration of the fluids.
• the lateral extent of the first liquid 12 is constrained to one electrowetting element by walls 16 or hydrophilic areas that follow the cross-section of the electrowetting cell. Further details of the electrowetting cell and its manufacture are disclosed amongst others in international patent application WO 2005/098797.
• the first liquid absorbs at least a part of the optical spectrum.
• the liquid may be transmissive for a part of the optical spectrum, forming a colour filter.
• the liquid may be coloured by addition of pigment particles or dye.
• the liquid may be black, i.e. absorb substantially all parts of the optical spectrum.
• the first liquid forms an electrically controllable light switch whereby the first and second liquids (12 and 11, respectively) are switchable between a first configuration of the liquids and a second configuration of the liquids.
• the first configuration corresponds with the position of the liquids 11, 12 when the first liquid 12 has the position indicated by dashed line 17.
• the second configuration corresponds with the position of the liquids 11, 12 when the first liquid 12 covers the hydrophobic layer 13.
• the first liquid 12 either covers the area of the electrode 14 or is removed from it.
• International patent application WO 2003/071346 discloses measures that allow the first liquid to cover the area of the electrode 14 only partially, thereby realising so-called grey level display states.
• the first and second liquids 12, 11 may flow back from the first configuration to eventually adopt the second configuration.
• the first liquid 12 becomes charged or polarised, the first liquid may consequently be more strongly attracted to the surface of the hydrophobic layer 13 than the second liquid 11. With a zero voltage applied, this effect does not occur. Thus, the energy of the electric field provided by application of the nonzero voltage may initiate the backflow.
• the first liquid 12 becomes sufficiently charged or polarised, the first liquid 12 tends to adhere to the hydrophobic layer 13 and flows back across the hydrophobic layer 13, with a rate dependent on the properties of for example a dye in the first liquid.
• the nonzero voltage With continued application of the nonzero voltage, the first liquid 12 flows back and eventually, the liquids 11, 12 adopt the second configuration. In the absence of any backflow, the hydrophobic layer 13 would otherwise be covered by the second liquid 11 in the first configuration.
• the charging of the first liquid 12, may be attributed to a polarity of an additive, such as a dye, in the first liquid 12.
• an additive such as a dye
• polar additive molecules With the application of the nonzero voltage, polar additive molecules are believed to orientate themselves with respect to the electric field created through the liquids. This orientation may be an alignment of the molecules with respect to other additive molecules and to the electric field. The polarity of the molecules in combination with such orientation may cause interaction with the second liquid 1 1 and possibly cause migration of ions from the second liquid 11 to the first liquid 12.
• electrowetting apparatus including a compound comprising a plurality of colorant moieties and a linker, the plurality of colorant moieties including a first colorant moiety having a first net dipole and a second colorant moiety having a second net dipole, wherein the plurality of colorant moieties are linked by and disposed around the linker so that the first net dipole and the second net dipole at least partially cancel each other.
• the electrowetting apparatus is the display device described above and illustrated by FIG. 1, and the compound of embodiments is provided in the first liquid.
• the compound has the general formula: (L)-(CM) n where L represents the linker, CM represents a colorant moiety, and n is an integer indicating the number of colorant moieties bonded to the linker, n having a value of 2, 3, 4 or more.
• a colorant moiety is a part of the compound which contributes to a colour property of the compound, and therefore has a characteristic absorption spectrum for light specific to that colorant moiety.
• Each of the colorant moieties may have at least one chromophore; a chromophore is a chemical group such as an azo group responsible for providing a colour property to the colorant moiety; for example the chromophore may be a conjugated chemical system.
• a colorant moiety may comprise a first azo group and a second azo group, which are not conjugated with each other.
• the linker does not include a chromophore and therefore does not substantially contribute to the colour properties of the compound.
• substantially contribute it is meant that the colour properties of the compound is primarily, i.e. 95% or more, contributed to by the plurality of colorant moieties rather than the linker, for example if the linker is not conjugated with the colorant moieties.
• the linker does not act as a chromophore or at least part of a chromophore.
• a bond between the linker and at least one colorant moiety may however contribute to the colour property of the compound.
• the plurality of colorant moieties are disposed around, i.e. are arranged around, the linker so that at least a first net dipole and a second net dipole of a first and second colorant moiety, respectively, at least partially cancel each other.
• the arrangement of the colorant moieties around the linker may be determined by the structure of the linker but may also be determined by stereochemical interactions of the colorant moieties with each other and/or with the linker.
• the examples of colorant moieties to be described are monovalent for bonding the linker, but in further examples a colorant moiety may have more than one valency for bonding to the linker.
• a net dipole of the compound may be reduced compared with the total dipole of the first and second net dipoles if arranged to add together.
• compounds described herein have a net dipole which is at least 50% less than the total dipole of the plurality of colorant moieties if arranged to add together.
• a compound has a net dipole which is at least 60%, 70%, 80%, 90%, 95% or 98% less than the total dipole of the plurality of colorant moieties.
• compound comprising the linker may reduce backflow.
• Compounds described herein can therefore provide the first fluid of the electrowetting apparatus with desirable colour properties, provided by the colorant moieties, but may also exhibit less backflow than if the colorant moieties were provided in the first fluid without being linked together.
• the net dipole of the compound may be substantially zero. In such embodiments, the compound may reduce or eliminate backflow from occurring when included in the first fluid.
• Substantially zero means the compound has no net dipole when depicted with an idealised geometry, but that the compound may have transient dipoles, for example through electron cloud variations and/or stereochemical changes when the compound is in situ, for example in the first fluid.
• the linker may have a net dipole.
• the linker may have a low net dipole or a net dipole of zero.
• dipole refers to a separation of charge between a first part of a molecule and a second part of a molecule.
• dipole means a dipole when an electric field is applied to the compound in question, for example the electric field applied for switching the first and second fluids to the first configuration. It is envisaged that although the term dipole herein relates to situations when an electric field is applied, it may also apply to situations where no electric field is applied.
• net dipole refers to an overall dipole of a compound; for example, the net dipole of a colorant moiety is the overall dipole of that colorant moiety.
• the net dipole is therefore the resulting dipole of a combination of individual dipoles, permanent and/or transient, of the compound in question.
• Such an individual dipole may for example lie along a bond between a more electronegative atom and a less electronegative atom.
• Compounds described according to embodiments represent a newly identified class of compounds for electrowetting apparatus, some of which may reduce backflow, for example when dissolved in the first fluid of electrowetting apparatus such as that described above.
• experimental data shows that some compounds can reduce backflow by at least 50%, and in other embodiments, at least 60%, 70%, 80%, 90%, 95% or 98%, when compared with the unlinked colorant moiety dissolved in the first fluid with the same optical density.
• At least some of the compounds described herein are novel.
• first colorant moiety and a second colorant moiety there is at least a first colorant moiety and a second colorant moiety.
• first colorant moiety and the second colorant moiety in embodiments are disposed around the linker so that the first net dipole and the second net dipole are at least partially opposed to each other; thus the first and second net dipoles at least partially cancel each other.
• first net dipole and the second net dipole completely oppose each other.
• the plurality of colorant moieties includes only the first and second colorant moieties, wherein when depicted with an idealised geometry the compound is substantially linear, the first net dipole and the second net dipole being substantially coincident along a linear axis.
• FIG. 2a illustrates such an embodiment; the first colorant moiety is labelled CMi, the second colorant moiety is labelled CM 2 , the first net dipole is labelled Di, the second net dipole is labelled D 2 and the linker is labelled L.
• the compound is linear along the linear axis LA.
• each colorant moiety has the same magnitude of net dipole, for example if each colorant moiety is the same, the net dipole of the compound is zero; i.e. the first and second net dipoles completely cancel each other.
• first and second colorant moieties may not lie along the linear axis LA, but that the compound is considered to be substantially linear as an angle o between the bonds linking each colorant moiety to the linker is in the range of 135 to 225 degrees.
• first and second net dipoles lie in the same direction as the bonds linking respectively the first and second colorant moieties to the linker.
• the first and second net dipoles are partially opposed and therefore partially cancel. This partial cancellation reduces the net dipole of the compound.
• At least a first and second net dipole are not coincident with a linear axis, or substantially linear.
• the first and second net dipoles Di, D 2 of the first and second colorant moieties CMi, CM2 may lie on different axes Axi and Ax 2 which are parallel with each other, or which are substantially parallel, i.e. within a range of 135 to 225 degrees, with each other; in this way the first and second net dipoles still at least partially oppose each other, resulting in at least partial cancellation of the first and second net dipoles.
• the linker and/or the colorant moieties are rigid, or their flexibility is limited; for example the linker and/or at least one of the plurality of colorant moieties is substantially planar, and may for example comprise a cyclic group such as a cycloakyl or an aryl; this can help maintain the spatial disposition of the colorant moieties around the linker, to maintain the relative position of the net dipoles of the colorant moieties when the compound is in an applied electric field, thus maintaining the at least partial cancellation of the net dipoles of the colorant moieties.
• substantially planar means at least three adjacent atoms of a core structure of a molecule lie in the same plane.
• the linker is divalent for linking the first and second colorant moieties.
• the linker may be divalent for only linking the first and second colorant moieties, or the linker may have at least one further valency for bonding to at least one non-colorant moiety.
• the linker has a general formula selected from the group consisting of: , i.e. a single bond; , i.e. a double bond; ,
• n independently 1, 2, 3, 4, 5, 6, 7 or 8
• X and Y are each independently selected from the group consisting of: hydrogen (H), a halogen atom, an alkyl group, an alkenyl group, an aryl group, an alkoxy group, and a thioalkyl group, and/or
• a pair of X and Y on the same carbon, taken together, is an oxo group, an acetal group or a thioacetal group, and
• T is oxygen (O) or sulphur (S).
• n is greater than 2
• the linker has a formula selected from the group
• the plurality of colorant moieties includes at least one further colorant moiety having at least one further net dipole, wherein the plurality of colorant moieties are disposed around the linker so that the first, second and at least one further net dipoles at least partially cancel each other.
• the at least one further colorant moiety comprises a third colorant moiety having a third net dipole
• the linker may be trivalent for linking the first, second and third colorant moieties.
• the linker may be trivalent for only linking the first, second and third colorant moieties, or the linker may have at least one further valency for bonding to at least one non-colorant moiety.
• the linker links the first, second and third colorant moieties in a disposition around the linker such that the first, second and third net dipoles at least partially cancel each other.
• each one of the first, second and third net dipoles are disposed around the linker to at least partially cancel each other of the first, second and third net dipoles; for example, each colorant moiety may be disposed around the linker such that each net dipole is spaced equally from the other net dipoles, and so the orientation of the net dipoles is such that they at least partially cancel each other.
• the colorant moieties may be disposed within the same plane, or may be disposed in three dimensional space.
• the linker is selected from the group consisting of:
• n independently 1, 2, 3, 4, 5, 6, 7, or 8
• Q is nitrogen (N) or phosphorus (P), and
• each of X 1 and Y 1 is independently selected from the group consisting of: a hydrogen atom (H) and an alkyl group , and/or
• the at least one further colorant moiety comprises a third colorant moiety having a third net dipole and a fourth colorant moiety having a fourth net dipole
• the linker may be tetravalent for linking the first, second, third and fourth colorant moieties.
• the linker may be tetravalent for only linking the first, second, third and fourth colorant moieties, or the linker may have at least one further valency for bonding to at least one non-colorant moiety.
• the linker links the first, second, third and fourth colorant moieties in a disposition around the linker such that the first, second, third and fourth net dipoles at least partially cancel each other.
• each one of the first, second, third and fourth net dipoles are disposed around the linker to at least partially cancel each other of the first, second, third and fourth net dipoles; for example, each colorant moiety may be disposed around the linker such that each net dipole is spaced equally from the other net dipoles, and so the orientation of the net dipoles is such that they at least partially cancel each other.
• the colorant moieties may be disposed within the same plane, or may be disposed in three dimensional space.
• the linker is selected from the group consisting of:
• n independently 1, 2, 3, 4, 5, 6, 7 or 8
• each of X 2 and Y 2 is independently selected from the groups consisting of: hydrogen (H) and an alkyl group, and/or
• alkyl 1 is an alkyl group having one or more carbon atoms, for example 1 to 32 carbon atoms.
• the third colorant moiety and the fourth colorant moiety are disposed around the linker so that the third net dipole and the fourth net dipole are at least partially opposed to each other; thus the third and fourth net dipoles may at least partially cancel each other.
• This may be in addition to the first and second colorant moieties being disposed around the linker so the first net dipole and the second net dipole are at least partially opposed to each other.
• the compound when the compound is depicted with an idealised geometry, the compound is symmetric in at least one plane bisecting a centre of the linker.
• the plane of symmetry may be a reflective symmetry plane dividing the compound into two halves, each half being a mirror image of the other half; in this way, the net dipoles of colorant moieties in one half at least partially cancel the net dipoles of colorant moieties in the other half.
• the compound may be rotationally symmetric in at least one plane, and in further examples the compound may be both reflectively and rotationally symmetric.
• the colour properties of the compound depend on the colorant moieties selected.
• each of the plurality of colorant moieties is the same colorant moiety. In such examples, it may therefore be easier to achieve at least partial cancellation of a net dipole of each colorant moiety, since each net dipole is the same.
• at least one of said plurality of colorant moieties is different from another one of said plurality of colorant moieties. In such examples different colorant moieties may be selected for linking by the linker, to tune the colour property to that desired of the compound.
• the compound is a dye.
• At least one of the plurality of colorant moieties is of a dye class selected from the group consisting of:
• each of A 1 to A 64 is independently selected from the group consisting of: a linker in accordance with any linker described herein, hydrogen (H), an alkyl group having one or more carbon atoms for example 1 to 32 carbon atoms, a halogen atom, an alkyl group, an alkenyl group, an oxo group group, an alkoxy group, a thiol group, a hydroxyl group, a thioalkyl group, an aryl group, a heteroaryl group, an amine group, a nitro group, a cyano group, an amide group, a sulphonyl group, a carboxy group, a trifluoromethyl group.
• H hydrogen
• At least one of the plurality of colorant moieties is an azo dye having a formula selected from the group consisting of:
• each Alkyl is independently an alkyl group having one or more carbon at ms, for example 1 to 32 carbon atoms,
• each of A 65 to A 68 is independently selected from the group consisting of: a linker in accordance with any linker described herein, hydrogen (H), an alkyl group comprising one or more carbon atoms for example 1 to 32 carbon atoms, a halogen atom, an alkyl group, an alkenyl group, an oxo group, an alkoxy group, a thiol group, a hydroxyl group, a thioalkyl group, an aryl group, a heteroaryl group, an amine group, a nitro group, a cyano group, an amide group, a sulphonyl group, a carboxy group, a trifluoromethyl group.
• H hydrogen
• Any alkyl group referred to herein includes any isomer of a straight chained, branched or cyclic alkyl group.
• there are one or more carbon atoms in the alkyl group for example within the range of 1 to 32 carbon atoms, and in other examples within the range of carbon atoms of Ci to Cio, i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.
• Any halogen atom referred to herein includes any of fluorine (F), chlorine (CI), bromine (Br) and iodine (I); in some examples a halogen atom is F or CI.
• Any alkenyl group referred to herein includes any isomers of a straight chained, branched or cyclic alkenyl group.
• there are one or more carbon atoms in the alkenyl group for example within the range of 1 to 32 carbon atoms, and in other examples within the range of carbon atoms of Ci to Cio, i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.
• Any aryl group referred to herein includes any aromatic hydrocarbon group having six or more carbon atoms, for example any aromatic hydrocarbon having C 6 to Cio carbon atoms, i.e. 6, 7, 8, 9 or 10 carbon atoms. Further, any such aryl group may be substituted on at least one aromatic carbon by for example, as defined herein, an alkyl group as defined herein, a halogen atom as defined herein, an alkenyl group as defined herein, an alkoxy group as defined herein, a thioalkyl group as defined herein, an oxo group as defined herein, an acetal group as defined herein or a thioacetal group as defined herein.
• Any alkoxy group referred to herein includes any isomer of an alkoxy group, i.e. an alkyl group, bonded to an oxygen, having one or more carbons, for example any isomer of an alkoxy having a number of carbon atoms in the range of 1 to 32, and in other examples a number of carbon atoms in the range of Ci to Cio, i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.
• Any thioalkyl group referred to herein includes any isomer of a thioalkyl group, i.e.
• an alkyl group, bonded to a sulphur, having one or more carbons for example any isomer of a thioalkyl having a number of carbon atoms in the range of 1 to 32, and in other examples a number of carbon atoms in the range of Ci to Cio, i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.
• An acetal group referred to herein includes two alkyl groups or an alkanediyl group bonded to each of two oxygen atoms.
• An alkanediyl group referred to herein is a divalent radical group with the formula -(CH 2 )ni- where nl is one or more, for example having an integer value in the range 1 to 32, and in some embodiments having an integer value in the range 1 to 10, i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.
• Such an alkanediyl may be straight chained or branched.
• a thioacetal group referred to herein includes two alkyl groups or an alkanediyl group bonded to each of two sulphur atoms.
• a thiol group referred to herein is the group SH.
• a hydroxyl group referred to herein is the group -OH.
• a heteroaryl group referred to herein includes any aromatic hydrocarbon group with at least one heteroatom, for example nitrogen (N) or oxygen
• the aromatic hydrocarbon group may include one or more carbon atoms, for example in the range Ci to Cio, i.e. 1, 2, 3, 4, 5, 6, 7, 8,
• An amine group referred to herein includes any primary, secondary or tertiary amine, i.e. -NH 2 substituted respectively with zero, one or two alkyl or aryl groups as defined herein.
• a nitro group referred to herein is the group -N0 2 , i.e. including a nitrogen atom bonded to two oxygen atoms.
• a cyano group referred to herein is the group -CN, i.e. a carbon atom bonded with a triple bond to a nitrogen.
• An amide group referred to herein is a group with a nitrogen bonded to a carboxy group, with the nitrogen being further substituted by two of a hydrogen atom, an alkyl group or an aryl group defined herein; i.e. -CON(AG) 2 where AG indicates an alkyl or aryl group defined herein.
• a sulphonyl group referred to herein is a group with a sulphur atom bonded to two oxygen atoms via two double bonds.
• the sulphur atom is further bonded by a single bond to a hydrocarbon group such as an alkyl or an aryl group labelled AG and defined herein; i.e. -S0 2 (AG).
• a carboxyl group referred to herein is the group COOH.
• a trifluoromethyl group referred to herein is the group-CF 3 .
• compounds described herein have desirable colour properties for an electrowetting display device and desirable lifetime properties, for example being resistant to photo-bleaching effects.
• compounds described herein have a suitable solubility for dissolving in the first fluid; the solubility may be adjusted in dependence on the length of alkyl groups on the colorant moieties, for example. Compounds described herein therefore are found to have properties well suited for use in the first fluid of electrowetting apparatus.
• a linker precursor may be a polyol or a polyamine; for example the linker precursor for the linker ⁇ ' may be
• the colorant moiety to be linked may have a carboxyl group, a halogen atom, a cyano group, an amine group, a hydroxyl group or a sulphonate group at the site to be linked.
• a method such as esterification, amidification, thioesterification, or etherification, may be used to link the linker and colorant moieties.
• Other techniques may include a cross coupling reaction, Friedel-Craft acylation or alkylation, or diazo coupling.
• linker L is -0-(CH2) 2 -0- and colorant moiety is represented as
• the linker precursor may be HO-(CH) 2 -OH and the colorant moiety to be linked may be represented by RCM-COOH, where RCM is the rest of the colorant moiety structure.
• An acid catalysed nucleophilic substitution reaction may be used for example to generate the compound RCM-CO-0-(CH) 2 -0-CO-RCM.
• linking can be achieved via the corresponding acid chloride or active ester as is known in the art.
• linker L is -NH-(CH) 2 -NH- and colorant moiety is represented as CM for example
• the linker precursor may be H 2 N-(CH) 2 -NH 2 and the colorant moiety to be linked may be represented by RCM-COOH, where RCM is the rest of the colorant moiety structure.
• An acid catalysed nucleophilic substitution reaction may be used for example to generate the compound RCM-CO-NH-(CH) 2 -NH-
• linking can be achieved via the corresponding acid chloride or active ester as is known in the art.
• linker L is -S-(CH) 2 -S- and colorant moiety is represented as
• the linker precursor may be HS-(CH) 2 -SH and the colorant moiety to be linked may be represented by RCM-COOH, where RCM is the rest of the colorant moiety structure.
• An acid catalysed nucleophilic substitution reaction may be used for example to generate the compound RCM-CO-S-(CH) 2 -S-CO-RCM.
• linking can be achieved via the corresponding acid chloride or active ester as is known in the art.
• the linker bonds to the colorant moieties using an alkyl group
• the linker may be coupled with the colorant moieties by cross coupling reaction, Friedel-Craft reaction, or nucleophile aromatic substitution.
• a linker precursor may be synthesised with one colorant moiety already linked; a subsequent reaction may be used to bond further colorant moieties to the linker.
• the linker may be synthesised with at least part of one colorant moiety linked; for example, where each colorant moiety is an azo, the azo groups may be formed after the part of the colorant moiety on one side of the azo group to be formed has been linked to the linker; another example of such a synthesis is illustrated in FIG. 3 where the linker is a cyclohexyl linker.
• This compound shows a 98% reduction in backflow when dissolved in the first fluid of electrowetting apparatus such as that described above, compared with the same apparatus but with the unlinked colorant moiety dissolved in the first fluid.
• This dye compound has a peak light absorption of 501 nanometres.
• the dye compound namely N,N"-((( IE, 1 * E)-((Piperazine- 1,4- dicarbonyl)bis(4, 1 -phenylene))bis(diazene-2, 1 -diyl))bis(3-(bis(2-ethylhexyl)amino)- 4-ethoxy-6,l-phenylene))bis(2-ethylhexanamide), may be synthesised by the following method:
• This compound shows a 98% reduction in backflow when dissolved in the first fluid of electrowetting apparatus such as that described above, compared with the same apparatus but with the unlinked colorant moiety dissolved in the first fluid.
• This dye compound has a peak light absorption of 628 nanometres.
• the dye compound namelyN,N'-(((lE, E)-((piperazine-l,4- dicarbonyl)bis(2,6-dicyano-4, 1 -phenylene))bis(diazene-2, 1 -diyl))bis(3-(bis(2- ethylhexyl)amino)-4-ethoxy-6, 1 -phenylene))bis(2-ethylhexanamide), may be synthesised by the following method:
• This compound shows a 57% reduction in backflow when dissolved in the first fluid of electrowetting apparatus such as that described above, compared with the same apparatus but with the unlinked colorant moiety dissolved in the first fluid.
• This dye compound has a peak light absorption of 550 nanometres.
• N,N'-(((lE,rE)-((piperazine-l,4-dicarbonyl)bis(2-nitro-4,l- phenylene))bis(diazene-2, 1 -diyl))bis(3-(bis(2-ethylhexyl)amino)-4-ethoxy-6, 1 - phenylene))bis(2-ethylhexanamide), may be synthesised as follows:
• Oxalyl chloride (6.40 g, 50.4 mmol) was added to an ice-cooled solution of 4-[(E)-2- ⁇ 4-[bis(2-ethylhexyl)amino]-5-ethoxy-2-(2- ethylhexanamido)phenyl ⁇ diazen-l-yl]-3-nitrobenzoic acid (7.13 g, 10.25 mmol). The mixture was stirred for 15 min in ice, then for 2 h at Room Temperature. 30% of the solution (i.e. 3.08 mmol acid chloride) was taken out and rotary evaporated.
• linker is which links two colorant moieties with the structure
• This dye compound has a peak light absorption of 506 nanometres.
• the dye compound namely (E)-N,N'-(ethane-l ,2-diyl)bis(4-((E)-(4-
• diazenyl)benzamide may be synthesised as follows:
• This dye compound has a peak light absorption of 508 nanometres.
• the dye compound namely (E)-2-(((4-((E)-(4-(bis(2- ethylhexyl)amino)-5-ethoxy-2-(2- ethylhexanamido)phenyl)diazenyl)benzoyl)oxy)methyl)propane- 1 ,3 -diyl bis(4-((E)- (4-(bis(2-ethylhexyl)amino)-5-ethoxy-2-(2- ethylhexanamido)phenyl)diazenyl)benzoate), may be synthesised as follows:
• This dye compound has a peak light absorption of 514 nanometres.
• the dye compound namely (E)-2,2-bis-(((4-((E)-(4-(bis(2- ethylhexyl)amino)-5-ethoxy-2-(2- ethylhexanamido)phenyl)diazenyl)benzoyl)oxy)methyl)propane- 1 ,3-diyl bis(4-((E)- (4-(bis(2-ethylhexyl)amino)-5-ethoxy-2-(2- ethylhexanamido)phenyl)diazenyl)benzoate), may be synthesised as follows:
• This dye compound has a peak light absorption of 518 nanometres.
• the dye compound namely (E)-l ,4-phenylene bis(4-((E)-(4-(bis(2- ethylhexyl)amino)-5-ethoxy-2-(2-ethylhexanamido)phenyl)diazenyl)benzoate), may be synthesised as follows:
• any stereoisomer of the compounds described herein may be applied in a first fluid of the electrowetting apparatus, to reduce backflow.
• embodiments may relate to dendrimers, compounds of some embodiments are not dendrimers as: there is one linker and no other branching points for colorant moieties; there are no more than four colorant moieties; and/or there is only one colorant moiety per arm of the compound, each arm stemming from the linker.
• the compounds may be applied more broadly, to potentially any technology other than that using electrowetting.
• the compound may be provided in a fluid of an electrowetting apparatus different from that described above, such as electrowetting apparatus comprising a support plate on which the fluid is provided and an electrode arranged relative to the fluid such that applying an electrical potential to the electrode changes a configuration of the fluid; an example of such apparatus may be an electrowetting lens, an electrowetting optical filter or a lab on chip device using electrowetting.

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