Lanthanide metal chelate security feature

Abstract

A chelate and associated security feature including a lanthanide metal and a ligand of formula (1), formula (2), or formula (3), ##STR00001##
where each of R.sub.1-R.sub.7 in formula (1) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic, where each of R.sub.1-R.sub.5 in formula (2) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe.sub.2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, and where R.sub.6 in formula (2) is selected from the group consisting of H, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe.sub.2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, and where each of R.sub.1-R.sub.5 in formula (3) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic.

Claims

1. A security feature for use in authenticating an article, comprising: a carrier; and an additive disposed in or on the carrier, wherein the additive is a chelate comprising: a lanthanide metal; and a ligand of formula (1), formula (2), or formula (3), ##STR00010## wherein each of R.sub.1-R.sub.7 in formula (1) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic, wherein each of R.sub.1-R.sub.5 in formula (2) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe.sub.2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, and wherein R.sub.6 in formula (2) is selected from the group consisting of H, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe.sub.2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, and wherein each of R.sub.1-R.sub.5 in formula (3) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic.

2. The security feature of claim 1, wherein the lanthanide metal is Europium.

3. The security feature of claim 1, wherein the ligand is a ligand of formula (1), wherein the ligand of formula (1) is a ligand of formula (5), wherein R.sub.1 in formula (5) is selected from the group consisting of H, F, OCF.sub.3, and CF.sub.3, and wherein each of R.sub.2 and R.sub.3 in formula (5) is independently selected from the group consisting of H, OH, and NH.sub.2 ##STR00011##

4. The security feature of claim 1, wherein the ligand is a ligand of formula (3), wherein the ligand of formula (3) is a ligand of formula (6), and wherein R in formula (6) is selected from the group consisting of H, F, OCF.sub.3, CF.sub.3, OMe, and OPh ##STR00012##

5. The security feature of claim 1, wherein the carrier is a paper substrate, a polymer substrate, an ink, a coating, a security thread, a fiber, or a planchette.

6. A method of authenticating an article, comprising: providing an article including a security feature; and irradiating the article with a radiation source to excite the security feature, wherein the security feature comprises: a carrier; and an additive disposed in or on the carrier, wherein the additive is a chelate comprising: a lanthanide metal; and a ligand of formula (1), formula (2), or formula (3), ##STR00013## wherein each of R.sub.1-R.sub.7 in formula (1) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic, wherein each of R.sub.1-R.sub.5 in formula (2) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe.sub.2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, and wherein R.sub.6 in formula (2) is selected from the group consisting of H, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe.sub.2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, and wherein each of R.sub.1-R.sub.5 in formula (3) is independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic.

7. The method of claim 6, wherein the lanthanide metal is Europium.

8. The method of claim 6, wherein the ligand is a ligand of formula (1), wherein the ligand of formula (1) is a ligand of formula (5), wherein R.sub.1 in formula (5) is selected from the group consisting of H, F, OCF.sub.3, and CF.sub.3, and wherein each of R.sub.2 and R.sub.3 in formula (5) is independently selected from the group consisting of H, OH, and NH.sub.2 ##STR00014##

9. The method of claim 6, wherein the ligand is a ligand of formula (3), wherein the ligand of formula (3) is a ligand of formula (6), and wherein R in formula (6) is selected from the group consisting of H, F, OCF.sub.3, CF.sub.3, OMe, and OPh ##STR00015##

10. The method of claim 6, wherein the carrier is a paper substrate, a polymer substrate, an ink, a coating, a security thread, a fiber, or a planchette.

11. The method of claim 6, wherein the radiation source is an ultraviolet (UV) light source.

12. The method of claim 6, wherein the article is a banknote, an ID document, a visa document, a tax stamp, a label, or a packaging.

13. The method of claim 6, wherein excitation of the security feature includes fluorescing of the security feature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows normalized emission spectra for a known compound and a compound of one embodiment of the present invention; and

(2) FIG. 2 shows excitation spectra for a known compound and a compound of one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) The present invention is directed to optical or visual security features based on particular fluorescent rare earth metal compounds, such as chelates composed of a lanthanide metal and a specific ligand, including the ligand of formula (1), formula (2), or formula (3). The lanthanide metal may be selected from any chemical element in the lanthanide series. In a preferred embodiment, the lanthanide metal is Europium.

(4) ##STR00008##

(5) Concerning the substituent groups for formulas (1)-(3), each of R.sub.1-R.sub.7 in formula (1) may be independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic, each of R.sub.1-R.sub.5 in formula (2) may be independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, R.sub.6 in formula (2) may be selected from the group consisting of H, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, NMe.sub.2, CN, alkyl, aryl, phenyl, OPh, and heteroaromatic, and each of R.sub.1-R.sub.5 in formula (3) may be independently selected from the group consisting of H, OH, NH.sub.2, Cl, F, OMe, OAr, OCF.sub.3, CF.sub.3, alkyl, aryl, phenyl, OPh, and heteroaromatic. The ligands of formulas (1)-(3) may exist in different tautomeric forms, and all such forms where such forms exist are included herein. Additionally, optical isomers and racemates of the ligands of formulas (1)-(3) where such forms exist are included herein.

(6) A non-limiting example of a ligand of formula (1) is a ligand of formula (5), where R.sub.1 in formula (5) may be selected from the group consisting of H, F, OCF.sub.3, and CF.sub.3, and each of R.sub.2 and R.sub.3 in formula (5) may be independently selected from the group consisting of H, OH, and NH.sub.2. A non-limiting example of a ligand of formula (3) is a ligand of formula (6), where R in formula (6) may be selected from the group consisting of H, F, OCF.sub.3, CF.sub.3, OMe, and OPh. A non-limiting example of a ligand of formula (5) is the ligand of formula (7), and a non-limiting example of a ligand of formula (6) is the ligand of formula (8).

(7) ##STR00009##

(8) Chelates composed of a lanthanide metal and a ligand of formulas (1)-(3) have been shown to demonstrate fluorescent emissions over a wide spectral band of wavelengths, particularly in the ultraviolet (UV) region, making these compounds suitable for use in security and authentication applications. In one non-limiting example, a red phosphor being a chelate of Europium and 4-hydroxy-2-quinoline carboxylic acid has been determined to possess superior emissive properties, including high spectral emissions and good light fastness in response to irradiation at atypical wavelengths, e.g., 280 nm. These properties resulting from the selection of 4-hydroxy-2-quinoline carboxylic acid as the desired ligand are unexpected, particularly in comparison to usage of 2-hydroxy-4-quinoline carboxylic acid, a known ligand, which fails to retain light fastness as such atypical wavelengths.

(9) Fluorescent rare earth metal compounds utilizing such known ligands, as disclosed in Potrawa et al. (US 20070051929 A1), have been described as fluorescing in response to irradiating sources having a wavelength of 366 nm. This wavelength is typically associated with low-pressure mercury lamps, which were the dominant, if not exclusive, UV light source for document security applications prior to the introduction of low-cost efficient UV-LEDs. These UV-LEDs have different peak wavelengths compared to low-pressure mercury lamps, in particular wavelengths in the range of 370 to 385 nm, thereby requiring the selection of compounds having fluorescence intensity attributes responsive to these different illumination wavelengths.

(10) FIG. 1 shows normalized emission spectra for a known compound, specifically 2-hydroxy-4-carboxylic acid Europium chelate (“Compound 2”), and a compound of one embodiment of the present invention, specifically 4-hydroxy-2-carboxylic acid Europium chelate (“Compound 1”). As illustrated in this emission spectra, both 2-hydroxy-4-carboxylic acid Europium chelate and 4-hydroxy-2-carboxylic acid Europium chelate are shown to have the same emission peak at 613 nm.

(11) FIG. 2 shows excitation spectra for a known compound, specifically 2-hydroxy-4-carboxylic acid Europium chelate (“Compound 2”), and a compound of one embodiment of the present invention, specifically 4-hydroxy-2-carboxylic acid Europium chelate (“Compound 1”). As illustrated in this excitation spectra, 2-hydroxy-4-carboxylic acid Europium chelate is more effective than 4-hydroxy-2-carboxylic acid Europium chelate when irradiated at wavelengths below 374 nm; however, at wavelengths above 374 nm, 4-hydroxy-2-carboxylic acid Europium chelate is superior. Moreover, while 4-hydroxy-2-carboxylic acid Europium chelate does not have the same maximum fluorescence brightness as 2-hydroxy-4-carboxylic acid Europium chelate, which occurs for 2-hydroxy-4-carboxylic acid Europium chelate when irradiated at wavelengths below 374 nm, 4-hydroxy-2-carboxylic acid Europium chelate fluoresces over a longer or wider spectral band of wavelengths than 2-hydroxy-4-carboxylic acid Europium chelate, particularly further in the region of the spectrum beyond 374 nm.

(12) The compounds of the present invention may be utilized in connection with security and authentication applications. Embodiments of the invention include systems and methods for document and product authentication based on irradiation and fluorescent emission detection. The compounds may be disposed in or on, or otherwise added to, a carrier material, the carrier material including but not limited to paper substrates, polymer substrates, inks, coatings, security threads, fibers, and planchettes, which can be utilized in the authentication and protection of items such as documents, currency, and secondary packaging for tobacco, luxury goods, and pharmaceuticals. Non-limiting examples of such items include banknotes, ID documents, visa documents, tax stamps, labels, and packaging. In an authentication method of present invention, an article includes a security feature disposed with a fluorescent rare earth metal compound, as has been described herein. The article is irradiated with a radiation source, particularly a UV light source, which may be in the range of 370 to 385 nm, greater than 374 nm, or simply not 365 or 366 nm, which results in excitation and fluorescence of the security feature by virtue of the fluorescent rare earth metal compound disposed therein or thereon.

(13) The embodiments and examples above are illustrative, and many variations can be introduced to them without departing from the spirit of the disclosure. For example, elements and/or features of different illustrative and exemplary embodiments herein may be combined with each other and/or substituted with each other within the scope of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated exemplary embodiments of the invention.