Thermal imaging members and methods   

This application claims the benefit of priority of provisional patent application Ser. Nos. 60/680,088 and 60/680,212, both filed May 12, 2005, the contents of which are incorporated herein by reference in their entireties.

This application is related to the following commonly assigned, United States patent applications and patents, the contents of which are incorporated herein by reference in their entireties:

U.S. Pat. No. 6,801,233 B2;

U.S. Pat. No. 6,906,735 B2;

U.S. Pat. No. 6,951,952 B2;

U.S. Pat. No. 7,008,759 B2;

U.S. patent application Ser. No. 10/806,749, filed Mar. 23, 2004, which is a division of U.S. Pat. No. 6,801,233 B2;

United States Patent Application Publication No. US2004/0176248 A1; (Attorney docket No. A-8544AFP);

United States Patent Application Publication No. US2004/0204317 A1; (Attorney Docket No. A-8586AFP);

United States Patent Application Publication No. US2004/0171817 A1; (Attorney Docket No. A-8589AFP);

U.S. patent application Ser. No. 11/400,735; filed on Apr. 6, 2006 (Attorney Docket No. A-8598);

U.S. patent application Ser. No. 11/400,734; filed on Apr. 6, 2006 (Attorney Docket No. A-8606); and

U.S. patent application Ser. No. ______; filed on even date herewith, Express Mail No.: EV 669114318 US (Attorney Docket No. A-8614).

FIELD OF THE INVENTION

This invention relates to thermal imaging members and methods and, more particularly, to such imaging members and methods in which there are utilized a color-former that exhibits one color in the crystalline form and a second, different color in the liquid, or amorphous, form.

BACKGROUND OF THE INVENTION

The development of thermal print heads (linear arrays of individually-addressable heating elements) has led to the development of a wide variety of thermally-sensitive imaging materials. In some of these, known as “thermal transfer” systems, heat is used to move colored material from a donor sheet to a receiver sheet. Alternatively, heat may be used to convert a colorless coating on a single sheet into a colored image, in a process known as “direct thermal” imaging. Direct thermal imaging has the advantage over thermal transfer of the simplicity of a single sheet. On the other hand, unless a fixing step is incorporated, direct thermal systems are still sensitive to heat after thermal printing. If a stable image is needed from an unfixed direct thermal system, the temperature for coloration must be higher than any temperature that the image is likely to encounter during normal use. A problem arises in that the higher the temperature for coloration, the less sensitive the imaging member will be when printed with the thermal print head. High sensitivity is important for maximum speed of printing, for maximizing the longevity of the print head, and for energy conservation in mobile, battery-powered printers. As described in more detail below, maximizing sensitivity while maintaining stability is more easily achieved if the temperature of coloration of a direct thermal medium is substantially independent of the heating time.

Thermal print heads address one line of the image at a time. For reasonable printing times, each line of the image is heated for about ten milliseconds or less. Storage of the medium (prior to printing or in the form of the final image) may need to be for years, however. Thus, for high imaging sensitivity, a high degree of coloration is required in a short time of heating, while for good stability a low degree of coloration is required for a long time of heating.

Most chemical reactions speed up with increasing temperature. Therefore, the temperature required for coloration in the short heating time available from a thermal print head will normally be higher than the temperature needed to cause coloration during the long storage time. Reversing this order of temperatures would be a very difficult task, but maintaining a substantially time-interval-independent temperature of coloration, such that the temperatures required for coloration over both long and short time intervals are substantially the same, is a goal that is achieved by the present invention.

There are other reasons why a time-interval-independent coloration temperature may be desirable. It may, for example, be required to perform a second thermal step, requiring a relatively long time of heating, after printing. An example of such a step would be thermal lamination of an image. The temperature of coloration of the imaging material during the time required for thermal lamination must be higher than the lamination temperature (otherwise the material would become colorized during lamination). It would be preferred that the imaging temperature be higher than the lamination temperature by as small a margin as possible. This would be the case for time-interval-independent temperature of coloration.

Finally, the imaging system may comprise more than one color-forming layer and be designed to be printed with a single thermal print-head, as described in the above-mentioned U.S. Pat. No. 6,801,233 B2. In one embodiment of the imaging system, the topmost color-forming layer forms color in a relatively short time at a relatively high temperature, while the lower layer or layers form color in a relatively long time at a relatively low temperature. An ideal topmost layer for this type of direct thermal imaging system would have time-interval-independent temperature of coloration.

Prior art direct thermal imaging systems have used several different chemical mechanisms to produce a change in color. Some have employed compounds that are intrinsically unstable, and which decompose to form a visible color when heated. Such color changes may involve a unimolecular chemical reaction. This reaction may cause color to be formed from a colorless precursor, the color of a colored material to change, or a colored material to bleach. The rate of the reaction is accelerated by heat. For example, U.S. Pat. No. 3,488,705 discloses thermally unstable organic acid salts of triarylmethane dyes that are decomposed and bleached upon heating. U.S. Pat. No. 3,745,009 reissued as U.S. Reissue Pat. No. 29,168 and U.S. Pat. No. 3,832,212 disclose heat-sensitive compounds for thermography containing a heterocyclic nitrogen atom substituted with an —OR group, for example, a carbonate group, that decolorize by undergoing homolytic or heterolytic cleavage of the nitrogen-oxygen bond upon heating to produce an RO+ ion or RO′ radical and a dye base or dye radical which may in part fragment further. U.S. Pat. No. 4,380,629 discloses styryl-like compounds that undergo coloration or bleaching, reversibly or irreversibly, via ring-opening and ring-closing in response to activating energies. U.S. Pat. No. 4,720,449 describes an intramolecular acylation reaction that converts a colorless molecule to a colored form. U.S. Pat. No. 4,243,052 describes pyrolysis of a mixed carbonate of a quinophthalone precursor that may be used to form a dye. U.S. Pat. No. 4,602,263 describes a thermally-removable protecting group that may be used to reveal a dye or to change the color of a dye. U.S. Pat. No. 5,350,870 describes an intramolecular acylation reaction that may be used to induce a color change. A further example of a unimolecular color-forming reaction is described in “New Thermo-Response Dyes: Coloration by the Claisen Rearrangement and Intramolecular Acid-Base Reaction”, Masahiko Inouye, Kikuo Tsuchiya, and Teijiro Kitao, Angew. Chem. Int. Ed. Engl., 31, pp. 204-5 (1992).

In all of the above-mentioned examples, control of the chemical reaction is achieved through the change in rate that occurs with changing temperature. Thermally-induced changes in rates of chemical reactions in the absence of phase changes may often be approximated by the Arrhenius equation, in which the rate constant increases exponentially as the reciprocal of absolute temperature decreases (i.e., as temperature increases). The slope of the straight line relating the logarithm of the rate constant to the reciprocal of the absolute temperature is proportional to the so-called “activation energy”. The prior art compounds described above are coated in an amorphous state prior to imaging, and thus no change in phase is expected or described as occurring between room temperature and the imaging temperature. Thus, as employed in the prior art, these compounds exhibit strongly time-interval-dependent coloration temperatures. Some of these prior art compounds are described as having been isolated in crystalline form. Nevertheless, in no case is there mentioned in this prior art any change in activation energy of the color-forming reaction that may occur when crystals of the compounds are melted.

Other prior art thermal imaging media depend upon melting to trigger image formation. Typically, two or more chemical compounds that react together to produce a color change are coated onto a substrate in such a way that they are segregated from one another, for example, as dispersions of small crystals. Melting, either of the compounds themselves or of an additional fusible vehicle, brings them into contact with one another and causes a visible image to be formed. For example, a colorless dye precursor may form color upon heat-induced contact with a reagent. This reagent may be a Bronsted acid, as described in “Imaging Processes and Materials”, Neblette\'s Eighth Edition, J. Sturge, V. Walworth, A. Shepp, Eds., Van Nostrand Reinhold, 1989, pp. 274-275, or a Lewis acid, as described for example in U.S. Pat. No. 4,636,819. Suitable dye precursors for use with acidic reagents are described, for example, in U.S. Pat. No. 2,417,897, South African Patent 68-00170, South African Patent 68-00323 and Ger. Offenlegungschrift 2,259,409. Further examples of such dyes may be found in “Synthesis and Properties of Phthalide-type Color Formers”, by Ina Fletcher and Rudolf Zink, in “Chemistry and Applications of Leuco Dyes”, Muthyala Ed., Plenum Press, New York, 1997. The acidic material may for example be a phenol derivative or an aromatic carboxylic acid derivative. Such thermal imaging materials and various combinations thereof are now well known, and various methods of preparing heat-sensitive recording elements employing these materials also are well known and have been described, for example, in U.S. Pat. Nos. 3,539,375, 4,401,717 and 4,415,633.

Prior art systems in which at least two separate components are mixed following a melting transition suffer from the drawback that the temperature required to form an image in a very short time interval by a thermal print-head may be substantially higher than the temperature required to colorize the medium during longer periods of heating. This difference is caused by the change in the rate of the diffusion needed to mix the molten components together, which may become limiting when heat is applied for very short periods. The temperature may need to be raised well above the melting points of the individual components to overcome this slow rate of diffusion. Diffusion rates may not be limiting during long periods of heating, however, and the temperature at which coloration takes place in these cases may actually be less than the melting point of either individual component, occurring at the eutectic melting point of the mixture of crystalline materials.

U.S. patent application Ser. No. 10/789,648, filed Feb. 27, 2004 (United States Patent Application Publication No. US2004/0176248 A1), and assigned to the same assignee as the present application, is directed to a thermal imaging method wherein a dye is converted from one form in which the dye has one color to another form in which the dye has a second color, e.g., from colorless to colored.

Japanese Published Application No. 9-241553 discloses inkjet recording inks containing certain asymmetrical rhodamine dyes. U.S. Pat. No. 4,390,616 discloses thermal imaging members and methods utilizing certain rhodamine dyes.

As the state of the imaging art advances and efforts are made to provide new imaging systems that can meet new performance, requirements, it would be advantageous to have thermal imaging systems which utilize yet another class of dyes.

SUMMARY

It is therefore an object of this invention to provide novel thermal imaging members and methods.

Another object of the invention is to provide such thermal imaging members and methods that utilize a color-former that exhibits different colors when in the crystalline form than when in the amorphous form.

Yet another object of the invention is to provide imaging members and methods that utilize certain rhodamine color-formers.

According to one aspect of the invention there are provided novel thermal imaging members and methods that utilize certain rhodamine color-forming compounds that exhibit a first color when in a crystalline form and a second color, different from the first color, when in an amorphous form.

In one embodiment of the invention there are provided novel thermal imaging members and methods that utilize compounds that are represented by formula I

wherein:

R1, R3, R4, R5, R6, R7, R8 and R14 are each independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, preferably having from 1 to 18 carbon atoms, alkenyl or substituted alkenyl, preferably having from 1 to 18 carbon atoms, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substituted alkoxy, substituted carbonyl, acylamino, halogen, aryl, substituted aryl, heteroaryl and substituted heteroaryl;

R2 is selected from the group consisting of hydrogen, alkyl or substituted alkyl, preferably having from 1 to 18 carbon atoms, alkenyl or substituted alkenyl, preferably having from 1 to 18 carbon atoms, heterocycloalkyl and substituted heterocycloalkyl; or

R2 and R3 taken together with the nitrogen atom to which they are attached can form a substituted or unsubstituted saturated heterocyclic ring system, such as, for example, substituted and unsubstituted morpholines, pyrrolidines, and piperidines;

R9 is absent or selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, preferably having from 1 to 18 carbon atoms, substituted or unsubstituted alkenyl, preferably having from 1 to 18 carbon atoms, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substituted alkoxy, substituted carbonyl, halogen, aryl, substituted aryl, heteroaryl, substituted heteroaryl, amino, substituted amino, alkylamino, substituted alkylamino, arylamino and substituted arylamino;

R10, R11 and R12 are each independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, preferably having from 1 to 18 carbon atoms, substituted or unsubstituted alkenyl, preferably having from 1 to 18 carbon atoms, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substituted alkoxy, substituted carbonyl, halogen, aryl, substituted aryl, heteroaryl, substituted heteroaryl, amino, substituted amino, alkylamino, substituted alkylamino, arylamino and substituted arylamino;

R13 is selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, preferably having from 1 to 18 carbon atoms, substituted or unsubstituted alkenyl, preferably having from 1 to 18 carbon atoms, heterocycloalkyl and substituted heterocycloalkyl;

R14 is selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, preferably having from 1 to 18 carbon atoms, substituted or unsubstituted alkenyl, preferably having from 1 to 18 carbon atoms, heterocycloalkyl and substituted heterocycloalkyl; or

R13 and R14 taken together with the atoms to which they are attached can form a 5- or 6-membered heterocyclic ring such as, for example, indoline or tetrahydroquinoline;

R15, R16, R17 and R18 are each independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, preferably having from 1 to 18 carbon atoms, substituted or unsubstituted alkenyl, preferably having from 1 to 18 carbon atoms, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substituted alkoxy, substituted carbonyl, halogen, aryl, substituted aryl, heteroaryl, substituted heteroaryl, amino, substituted amino, alkylamino, substituted alkylamino, arylamino and substituted arylamino;

X1 is carbon or nitrogen; and at least one of R2 and R13 is hydrogen.

The substituents are preferably chosen to minimize the water solubility of the compounds and facilitate the formation of a colorless form in non-polar, non-protic solvents. In turn, the colorless lactone form of the compounds must be capable of melting to form the colored form.

A preferred group of compounds for use according to the invention are those represented by formula I wherein R2 and R3 taken together form a pyrrolidine ring, R10, R11 and R13 each is hydrogen, X1 is carbon and R1, R4, R5, R6, R7, R8, R9, R12, R14, R15, R16, R17 and R18 are as previously described with respect to formula I.

A second preferred group of compounds for use according to the invention are those represented by formula I wherein R2 is hydrogen, R3 is alkyl, R10 and R11 are each halogen, R13 is alkyl, X1 is carbon and R1, R4, R5, R6, R7, R8, R9, R12, R14, R15, R16, R17 and R18 are as described with respect to formula I.

A third preferred group of compounds for use according to the invention are those represented by formula I wherein R2 is hydrogen, R3 is aryl or substituted aryl, R13 and R14 are alkyl and R1, R4, R5, R6, R7, R8, R9, R10, R11, R12, R15, R16, R17, R19 and X1 are as described with respect to formula I.

Particularly preferred rhodamine compounds for use according to the invention are those represented by formula I in which R1, R4, R5, R6, R7, R8, R9 and R12 are each hydrogen; R2 is hydrogen or alkyl having from 1-18 carbon atoms, R3 is alkyl having from 1-18 carbon atoms, aryl or substituted aryl, or R2 and R3 taken together with the nitrogen atom to which they are attached form a pyrrolidine ring; R10 and R11 are each independently hydrogen or halogen; R13 is hydrogen or alkyl, preferably having from 1-18 carbon atoms, R14 is hydrogen or alkyl having from 1-18 carbon atoms, X1 is carbon and R15, R16, R17 and R18 are each independently hydrogen, alkyl having from 1-18 carbon atoms, or halogen.

The conversion from the crystalline form to the amorphous form in accordance with the thermal imaging members and thermal imaging methods of the invention is carried out by applying heat to the compounds. In the thermal imaging methods of the invention thermal energy may be applied to the thermal imaging members by any of the techniques known in thermal imaging such as from a thermal print head, a laser, a heated stylus, etc.

In another embodiment, one or more thermal solvents, which are crystalline materials, can be incorporated in the thermal imaging member. The crystalline thermal solvent(s), upon being heated, melt and dissolve or liquefy, and thereby convert, at least partially, the crystalline color-forming material to the amorphous form to form the image.

When converted to the colored form the compounds of formula I have the open form illustrated by formula II (for the case where R2 in formula I is hydrogen)

or formula III (for the case where R13 in formula I is hydrogen).

wherein R1, R3-R18, and X1 are as defined above with respect to formula I.

According to the invention the compounds of formula I may be incorporated in any thermal imaging members and used in any thermal imaging methods including thermal transfer imaging members and methods and direct thermal imaging members and methods. The thermal imaging members of the invention may be for use in thermal transfer imaging such as is disclosed in U.S. Pat. No. 6,537,410 B2. Conventional methods for color thermal imaging such as thermal wax transfer printing and dye-diffusion thermal transfer typically involve the use of separate donor and receiver materials. The donor material typically has a colored image-forming material, or a color-forming imaging material, coated on a surface of a substrate and the image-forming material or the color-forming imaging material is transferred thermally to the receiver material. In order to make multicolor images, a donor material with successive patches of differently-colored, or different color-forming, material may be used. In the case of printers having either interchangeable cassettes or more than one thermal head, different monochrome donor ribbons are utilized and multiple color separations are made and deposited successively above one another.

The thermal imaging members according to the invention may be for use in direct thermal printing methods and such thermal imaging members include all the color-forming reagents necessary to form an image in the member. Such direct thermal imaging members according to the invention may be used in any direct thermal imaging method such as, for example, disclosed in U.S. Pat. No. 6,801,233 B2.

Thermal imaging members according to the invention generally comprise a substrate carrying at least one image-forming layer including a compound according to formula I in the crystalline form, which can be converted, at least partially to an amorphous form, the amorphous form having intrinsically a different color from the crystalline form. The imaging member may be monochromatic, in which an image-forming layer includes at least one compound of formula I, or polychromatic. Multicolor direct thermal imaging members include at least two, and preferably three, image-forming layers and the temperature at which an image is formed in at least one of the image-forming layers is preferably time-interval-independent. Preferred imaging members according to the invention are direct multicolor thermal imaging members.

Any suitable thermal solvents may be incorporated in the thermal imaging members of the invention. Suitable thermal solvents include, for example, alkanols containing at least about 12 carbon atoms, alkanediols containing at least about 12 carbon atoms, monocarboxylic acids containing at least about 12 carbon atoms, esters and amides of such acids, aryl sulfonamides and hydroxyalkyl-substituted arenes.

Specific preferred thermal solvents include: tetradecan-1-ol, hexadecan-1-ol, octadecan-1-ol, dodecane-1,2-diol, hexadecane-1,16-diol, myristic acid, palmitic acid, stearic acid, methyl docosanoate, 1,4-bis(hydroxymethyl)benzene, and p-toluenesulfonamide.

Particularly preferred thermal solvents are diaryl sulfones such as diphenylsulfone, 4,4′-dimethyldiphenylsulfone, phenyl p-tolylsulfone and 4,4′-dichlorodiphenylsulfone.

It is possible that the dissolution of the compounds of formula I by a thermal solvent may lead to an amorphous form (in which the compound is dissolved in the amorphous thermal solvent) in which the proportion of the open, colored form is different from the proportion that would be present in the amorphous form resulting from melting the compound of formula I alone (i.e., without interaction with the thermal solvent). In particular, the proportion of the open, colored form of the compound in the amorphous material may be enhanced by use of hydrogen-bonding or acidic thermal solvents. Materials that increase the proportion of the color-forming material that is in the open, colored form are hereinafter referred to as “developers”. It is possible that the same compound may serve the function of thermal solvent and developer. Preferred developers include phenols such as 2,2′-methylenebis(6-tert-butyl-4-methylphenol), 2,2′-methylenebis(6-tert-Butyl-4-Ethyl-Phenol), 2,2′-ethylidenebis(4,6-di-tert-butylphenol), bis[2-hydroxy-5-methyl-3-(1-methylcyclohexyl)phenyl]-methane, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate, 2,6-bis[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl]-4-methyl-phenol, 2,2′-butylidenebis[6-(1,1-dimethylethyl)-4-methyl-phenol, 2,2′-(3,5,5-trimethylhexylidene)bis[4,6-dimethyl-phenol], 2,2′-methylenebis[4,6-bis(1,1-dimethylethyl)-phenol, 2,2′-(2-methylpropylidene)bis[4,6-dimethyl-phenol], 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 2,2′-thiobis(4-tert-octylphenol), and 3-tert-butyl-4-hydroxy-5-methylphenyl sulfide.

In order for the image formed by the amorphous color-former to be stable against recrystallization back to the crystalline form, preferably the glass transition temperature (Tg) of the amorphous mixture of the color-former and any thermal solvent should be higher than any temperature that the final image must survive. Typically, it is preferred that the Tg of the amorphous, colored material be at least about 50° C., and ideally above about 60° C. In order to ensure that the Tg is sufficiently high for a stable image to be formed, materials having a high Tg may be added to the color-forming composition. Such materials, hereinafter referred to as “stabilizers”, when dissolved in the amorphous mixture of color-former, optional thermal solvent, and optional developer, serve to increase the thermal stability of the image.

Preferred stabilizers have a T9 that is at least about 60° C., and preferably above about 80° C. Examples of such stabilizers are the aforementioned 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate (Tg 123° C.) and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (Tg 101° C.). It will be clear that the stabilizer molecule may also serve as a thermal solvent or as a developer.

For example, the color-forming material may itself have a melting temperature above the desired temperature for imaging, and a Tg (in the amorphous form) of about 60° C. In order to produce a color-forming composition melting at the desired temperature, it may be combined with a thermal solvent (for example, a diaryl sulfone) that melts at the desired temperature for imaging. The combination of thermal solvent and color-forming material may, however, have a Tg that is substantially lower than 60° C., rendering the (amorphous) image unstable. In this case, a stabilizer such as 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate may be added, to raise the Tg of the amorphous material. In addition, there may be provided a developer, for example, a phenolic compound such as 2,2′-ethylidenebis(4,6-di-tert-butylphenol), in order to increase the proportion of the color-forming material that is in the colored form in the amorphous phase.

Preferably the color-forming compound of the present invention, the (optional) thermal solvent, the (optional) developer and the (optional) stabilizer are each predominantly in their crystalline forms prior to imaging. By “predominantly” is meant at least about 50%. During imaging, at least one of these materials melts and an amorphous mixture of the materials is formed. The amorphous mixture is colored, whereas the crystalline starting materials are not.

It is possible that one of the components in the amorphous, colored mixture may recrystallize after the image has been formed. It is desirable that such recrystallization not change the color of the image. In the case that a color-former, thermal solvent, developer and stabilizer are used, the thermal solvent may typically recrystallize without greatly affecting the color of the image.

Preferred thermal imaging members according to the invention are direct thermal imaging members, particularly those having the structures described in commonly assigned U.S. Pat. No. 6,801,233 B2.

Other preferred thermal imaging members are those for use in thermal transfer imaging methods, particularly those having the structures described in commonly assigned U.S. Pat. No. 6,537,410.

Further preferred thermal imaging members are thermal transfer imaging members having the structures described in commonly assigned U.S. Pat. No. 6,054,246.

DETAILED DESCRIPTION

Compounds in the crystalline state commonly have properties, including color, that are very different from those of the same compounds in an amorphous form. In a crystal, a molecule is typically held in a single conformation (or, more rarely, in a small number of conformations) by the packing forces of the lattice. Likewise, if a molecule can exist in more than one interconverting isomeric form, only one of such isomeric forms is commonly present in the crystalline state. In amorphous form or solution, on the other hand, the compound may explore its whole conformational and isomeric space, and only a small proportion of the population of individual molecules of the compound may at any one time exhibit the particular conformation or isomeric form adopted in the crystal. Compounds of the present invention exhibit tautomerism in which at least one tautomeric form is colorless, and at least another tautomeric form is colored. The crystalline form of compounds of the present invention comprises predominantly the colorless tautomer.

In a first embodiment of the invention there are provided thermal imaging members and methods which utilize a compound whose colorless tautomer is represented by formula I as described above.

Specific representative compounds utilized according to the invention are those of formula I which are shown in Table I in which the substituents R1, R4, R5, R6, R7, R8, R9, R11, R15, R17, R18 are all hydrogen, X1 is carbon and R2, R3, R10, R11, R13, R14 and R16 are as shown:

TABLE I DYE R2 R3 R10 R11 R13 R14 R16 M.P. λmax I n-C10H21 H H H —(CH2)3— H 124 570 II 2-EtPh H H H  C8H17 C2H5 H 144 548 III Ph H H H C4H9 H H 172 552 IV 2-MePh H H H  C8H17 CH3 H 152 548 V 2-MePh H H H  C6H13 CH3 H 199 548 VI 2-MePh H H H C4H9 H H 184 550 VII Cyclohexyl H H H C2H5 H H 212 544 VIII Adamantyl H H H

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