Time-temperature indicator based on valence isomerizations

1. A time-temperature indicator for indicating a temperature change over time, comprising:

(a) at least one indicator compound selected from the group consisting of a diarylethene compound and a spiroaromatic compound in a first isomeric form, which is converted into a second isomeric form of said indicator compound in a valence isomerization reaction without migration of an atom or chemical group attached to said indicator compound in a time and temperature dependent manner, wherein the formation of the second isomeric form is detectable by monitoring a physical characteristic of the first isomeric form or the second isomeric form of the indicator, and

(c) a color filter that substantially filters out only the wavelength ranges causing undesirable renewed coloration of the indicator after the time-temperature clock has started.

2. The time-temperature indicator of claim 1 , wherein the diarylethene is a compound of Formula (I)

wherein:

R 1 and R 2 each independently represent C6-C14 aryl, C4-C12 heteroaryl, conjugated heterocyclic; wherein said heteroaryl and conjugated heterocyclic may contain one to three heteroatoms selected from the group consisting of N, O, and S; and wherein said aryl, heteroaryl, or conjugated heterocyclic may be substituted by one or more halogen, hydroxyl, thiol, amino, C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic, cyano, nitro, sulfo, —CH═CH—CN, azido, or amido;

R 1 ′ and R 2 ′ each independently represent H, cyano, nitro, sulfo, hydroxyl, thiol, —CH═CH—CN, or amido; or substituted or unsubstituted C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic; or R 1 ′ and R 2 ′ together with the carbon atoms to which they are attached form a C5-C8 carbocyclic ring or a C4-C7 heterocyclic ring containing one to three endocyclic or exocyclic heteroatoms selected from the group consisting of N, O, and S; said N heteroatom may be further substituted by H, or by one or two substituted or unsubstituted groups selected from the group consisting of C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic, hydroxyl, and —CH═CH—CN; when said N heteroatom is tetrasubstituted it is positively charged and is associated with an anion selected from the group consisting of organic and inorganic anions, and optionally wherein said C5-C8 carbocycle is substituted by one or more halogen; and optionally

R 1 , R 1 ′, R 2 and R 2 ′ each independently represent a charged group or a group substituted by another group having a charge; said charge may be localized or delocalized and may be positive or negative;

and wherein said R 1 and R 2 are in a cis or trans conformation.

3. The time-temperature indicator of claim 2 , wherein the diarylethene is

(a) a symmetric diarylethene selected from the group consisting of 1,2-dicyano-1,2-bis(2,4,5-trimethylthiophene-3-yl)ethane (1); 2,3-bis(2,4,5-trimethylthiophene-3-yl)maleic anhydride (2); 1,2-bis(2-cyano-1,5-dimethyl-4-pyrrolyl)perfluorocyclopentene (3); and 1,2-bis(2,4-dimethyl-5-phenylthiophene-3-yl)perfluorocyclopentene (4); or

(b) an asymmetric diarylethene selected from the group consisting of 2-(1,2-dimethyl-3-indolyl)-3-(2,4,5-trimethyl-3-thienyl)maleic anhydride (5); and 2-(methoxybenzo[b]thiophene-3-yl)-3-(1,2-dimethyl-3-indolyl)maleic anhydride (6).

4. The time-temperature indicator of claim 1 , wherein the spiroaromatic compound is a compound of Formula (II):

wherein:

ring A represents a C5-C8 carbocycle, C4-C7 heterocycle containing at least one heteroatom selected from the group consisting of N, O, and S; said N heteroatom may be further substituted by one or two groups selected from the group consisting of C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic, hydroxyl, and —CH═CH—CN; when said N heteroatom is tetrasubstituted it is positively charged and is associated with an anion selected from the group consisting of organic and inorganic anions; said C5-C8 carbocycle or C4-C7 heterocycle may be substituted by one or more of the groups selected from the group consisting of halogen, C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic, cyano, nitro, sulfo, hydroxyl, thiol, —CH═CH—CN, azido, amido and amino;

ring B represents a substituted or unsubstituted heterocycle containing at least one heteroatom X, said X being selected from the group consisting of N, O, and S; wherein said N atom may be further substituted by one or two groups selected from the group consisting of C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic, hydroxyl, and CH═CH—CN; when said N heteroatom is tetrasubstituted it is positively charged and is associated with an anion selected from the group consisting of organic and inorganic anions;

and wherein said ring B may contain one or more endocyclic double bonds and is optionally substituted by one or more halogen;

said rings A and B may be fused to one or more substituted or unsubstituted carbocycle, C4-C14 heterocycle, C6-C14 aryl or C4-C14 heteroaryl ring system;

and wherein the compounds of Formula (II) may be neutral, charged, multiply charged, positively charged having an external anion, negatively charged having an external cation or zwitterionic.

5. The time-temperature indicator of claim 4 , wherein the spiroaromatic compound is a spiropyran derivative.

6. The time-temperature indicator of claim 4 , wherein the spiropyran derivative is a derivative of 1′,3′,3′-trimethyl-6-nitro-spiro(2H-1-benzopyran-2,2′-2H-indole) of Formula (III):

wherein:

R3 is selected from the group consisting of H, halogen, C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic, and azido; wherein said alkyl, alkenyl, alkynyl, aryl, heteroaryl, and non-aromatic carbocycle may be substituted by one or more group selected from the group consisting of halogen, hydroxyl, thiol, amino, alkoxy, nitro, azido, and sulfo;

R4 is selected from the group consisting of C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, C1-C6 alkanoyl, C1-C6 alkoxy, C1-C6 alkylthio, C6-C14 aryl, C4-C14 heteroaryl, C3-C8 membered non-aromatic carbocyclic, C3-C8 membered ring non-aromatic heterocyclic, hydroxyl and —CH═CH—CN; and

Y is selected from the group consisting of C1-C25 alkyl and C7-C15 aralkyl, wherein said alkyl and aralkyl is optionally substituted by one or more halogen.

7. The time-temperature indicator of claim 4 , wherein the spiroaromatic compounds include at least one of the following: spirooxazine or its derivatives, spironaphthoxazine or its derivatives, and spiroindolinopyridobenzoxazine or its derivatives.

8. The time-temperature indicator of claim 1 , wherein the spiroaromatic compound is a compound of Formula (IV):

wherein:

A and L are independently of each other selected from the group consisting of H, halogen, C2-C12 alkenyl, C2-C12 alkynyl and

wherein R is C1-C6 alkyl, C1-C6 alkoxy, C6-C14 aryl and C7-C15 aralkyl; wherein said alkenyl, alkynyl and

may be substituted by one or more groups selected from the group consisting of halogen, hydroxyl, thiol, amino, alkoxy, nitro, azido, sulfo, aryl and heteroaryl;

Y is selected from the group consisting of C1-C25 alkyl and C7-C15 aralkyl, wherein said alkyl and aralkyl is optionally substituted by one or more halogen; and

X is C1-C6 alkoxy or L;

with the proviso that Y is not n-propyl when L, A and X are hydrogen.

9. The time-temperature indicator of claim 8 , wherein

L is hydrogen, Cl, Br or I;

Y is methyl, n-propyl, n-octadecyl or

X is hydrogen or methoxy; and

A is hydrogen;

with the proviso that Y is not n-propyl when L and X are hydrogen.

10. A printing ink or printing ink concentrate, comprising the time-temperature indicator of claim 8 .

11. A high molecular weight material, comprising the time-temperature indicator of claim 8 .

12. A method of manufacturing the time-temperature indicator of claim 1 , comprising the steps of

(a) embedding in or atop a matrix at least one indicator compound selected from the group consisting of a diarylethene compound and a spiroaromatic compound;

(b) inducing the formation of a metastable state of said embedded indicator compound; and

(c) covering the time-temperature indicator with a color filter that substantially filters out only the wavelength ranges causing undesirable renewed coloration of the indicator after the time-temperature clock has started.

13. The time-temperature indicator of claim 5 , wherein the spiropyran derivative is selected from the group consisting of 1′,3′,3′,8-tetramethyl-5-hydroxymethyl-spiro(2H-pyrano[2,3-c]pyridine-2,2′-2H-indole) and 1′,3′,3′,8-tetramethyl-spiro(2H-pyrano[2,3-c]pyridine-2,2′-2H-indole).

14. The time-temperature indicator of claim 6 , wherein in Formula (III) Y is selected from the group consisting of C1-C25 alkyl and C7-C15 aralkyl, wherein said alkyl and aralkyl are substituted by one or more fluorine.

15. The time-temperature indicator of claim 8 , wherein in Formula (IV) Y is selected from the group consisting of C1-C25 alkyl and C7-C15 aralkyl, wherein said alkyl and aralkyl are substituted by one or more fluorine.

16. A printing ink or printing ink concentrate, comprising the time-temperature indicator of claim 9 .

17. A high molecular weight material, comprising the time-temperature indicator of claim 9 .

18. The time-temperature indicator of claim 1 , wherein the spiroaromatic compound has the formula

wherein L is hydrogen, Y is

and X is methoxy.

19. A packaging material or a label that comprises a time-temperature indicator for indicating a temperature change over time, comprising:

(a) at least one indicator compound selected from the group consisting of a diarylethene compound and a spiroaromatic compound in a first isomeric form, which is converted into a second isomeric form of said indicator compound in a valence isomerization reaction without migration of an atom or chemical group attached to said indicator compound in a time and temperature dependent manner, wherein the formation of the second isomeric form is detectable by monitoring a physical characteristic of the first isomeric or the second isomeric form of the indicator

(c) a color filter that substantially filters out only the wavelength ranges causing undesirable renewed coloration of the indicator after the time-temperature clock has started, and

(b) a reference scale or reference color for evaluating the degree of decoloration or coloration.

20. The time-temperature indicator of claim 2 , wherein R 1 ′ and R 2 ′ together with the carbon atoms to which they are attached form a C5-C8 carbocyclic ring, wherein the C5-C8 carbocyclic ring is substituted by one or more fluorine atoms.

21. The time-temperature indicator of claim 1 , further comprising a reference scale for evaluating the degree of decoloration or coloration.

22. The time-temperature indicator of claim 21 , wherein the reference scale is a reference color.

23. The time-temperature indicator of claim 1 , wherein the at least one indicator compound is present in a crystalline form.