WO2021044264A1

WO2021044264A1 - Detecting temperature abuse

Info

Publication number: WO2021044264A1
Application number: PCT/IB2020/058025
Authority: WO
Inventors: Magnus RUEPING; Srinivas Banala; Jean Michel MERKES
Original assignee: King Abdullah University Of Science And Technology
Priority date: 2019-09-03
Filing date: 2020-08-27
Publication date: 2021-03-11

Abstract

The present disclosure provides oxadiazaborinine (ODB) dyes represented by Formula (I) wherein each of R₁ through R₇ are independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and each X is halogen; and wherein the ODB dye exhibits an irreversible conversion to a dipyrrometheneboron difloro-based chromophore or fluorophore when exposed to a temperature at or greater than a predetermined threshold temperature. Articles and devices comprising ODB dyes for use as Time-Temperature Indicators and methods of detecting temperature abuse are described.

Description

DETECTING TEMPERATURE ABUSE

BACKGROUND

[0001] Temperature greatly affects the quality and safety of food (e.g., frozen seafood) and sensitive pharmaceutical and biological products such as blood products and vaccines. A qualitative, visual color change, analysis can be used to detect changes on food properties due to this alteration process. However, performing such analysis may not be always available. Whereas packaged frozen products are ubiquitous in everyday life, visible markers indicating temperature changes during their distribution are not in routine use. [0002] Existing technologies for detecting temperature abuse are highly expensive and are not suitable for use in a broad range of everyday applications. Electronic temperature logs are expensive, thus can be used only in high-end applications, such as systems for remote monitoring of temperature and transport data loggers. Probes providing a visual marker of temperature abuse have the potential to be highly valuable as time- temperature indicators (TTIs) for cooled or refrigerated products. Yet, previously developed TTIs for monitoring refrigerated and frozen food products have mainly used viscous liquids in capillary flow, and thermochromic dyes and are associated with various disadvantages, including an inability to detect abrupt rises in temperature over a short period of time due to existing constant flow rate, reversible and photosensitive color conversion. Hence, broad usage of these existing TTI indicators has been limited and there is a high demand for alternative solutions.

[0003] A probe that provided a visual marker of temperature abuse would be highly useful identifying temperature changes as a time-temperature indicator (TTI) for cooled or refrigerated products. In particular, there is a need for probes that can be used as temperature abuse indictor which can be integrated into packaging or labels, and allow reliable evidence of temperature abuse by producing detectable change in color and fluorescence upon deviation from frozen (-20 °C) to room temperature and above. A simple organic dye that is inexpensive to prepare, easy to handle, non-toxic, easy to dispose of, and which exhibits irreversible color changes on warming would represent a practical and significant advantages as a TTI. Such a temperature sensitive dye could also be useful for improving temperature control of supply chains and product storage conditions, and may also have potential uses in biomedical imaging, hyperthermia detection and monitoring, and nano-heating technologies.

SUMMARY

[0004] In general, the present disclosure features oxadiazaborinines (ODBs), which are a class of organic dyes that undergo one or more of a visible color change or a detectable change in fluorescence in response to a rise in temperature. The change is irreversible upon cooling, stable upon further warming, and is not photosensitive. This temperature sensitivity can be exploited for use as a Time-Temperature Indicator (TTI) for the detection of temperature abuse. For example, an ODB can exhibit a color change when warmed from frozen state to 4 °C and above. Accordingly, one or more embodiments of the present disclosure describe an indicator system which is responsive at a temperature- dependent rate to yield a visually-distinct indication of thermal abuse. This irreversible and visible change informs the consumer about the improper storage, and to refrain from consumption of the product.

[0005] In one aspect, the present disclosure features a oxadiazaborinine (ODB) dye represented by formula (I):

wherein each of R₁ through R₇ are independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and each X is halogen; and wherein the ODB dye exhibits an irreversible conversion to a dipyrrometheneboron difluoro-based chromophore or fluorophore when exposed to a temperature at or greater than a predetermined threshold temperature. R1-R₇ can be independently selected from: H, halogen, nitrile, isonitrile, nitroso, nitro, amine, isocyanate, carbonyl, phenyl, naphthyl, pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, ArF, ArN2, and NHCOAr where Ar is phenyl or naphthyl, C_nH_2n-1, where n is an integer from 1 to 4, CF_2n-1, CnH_2nF_2n+1, (CF_2n+1)CO, C02C F_2n-1, (CH₂)nF, (CH₂)nCl, (CH₂)nBr, (CH₂)nI, (CH₂)nCN, (CH₂)nNC, (CH₂)_nNO₂, (CH₂)nNO, (CH₂)nCO(CnF_2n-1), (CH2)nCO₂H, and (CH2)_nNH2, where n is an integer from 1 to 3, SO3M and CO2M where M is Na or K, cyclic alkyl groups having the formula C_nH_2n-1 where n is an integer from 4 to 6, C_nH_2n-2 and olefin derivatives having the formula C_nH_2n-1 where n is an integer from 2 to 4, RCO, CO2R, CONHR, CON(R)2, NHR, N(R) , NHCOR, C(NOR)R, SO3R, SO2R, PO3R, (CH₂)nCOR, (CH₂)nS0 R, (CH2)nSO₂R, (CH₂)_nNHR, (CH₂)nN(R)2, and (CH₂)nNHCOR where R=C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4, (CH₂)_nAr, (CH₂)_nArN2, and (CH2)_nNHCOAr where Ar= phenyl or naphthyl and n is an integer from 1 to 4, (CH₂)_nHET where HET is pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, or isothiazolyl and n is an integer from 1 to 3, and (CH₂)_nSO₃M where M is Na or K and n is an integer from 1 to 4 alone or in combination; and R₈ can be C. R₁, R4, R₅ and R₆ can all be C_nH_2n-1, where n is an integer from 1 to 4, R2, R3, and R₇ can be H, and R₈ can be C. The OBD can have the structure of Formula (II):

wherein at least one X is fluorine. The predetermined threshold temperature can be selected from the group consisting of about -18 °C, about -10 °C, about 1 °C, about 4 °C, or about 10 °C. [0006] In another aspect, the present disclosure features a Time-Temperature Indicator (TTI) comprising a first reservoir containing an oxadiazaborinine (ODB) dye represented by formula (I):

wherein each of R₁ through R₇ can be independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and each X is halogen; wherein the ODB dye exhibits irreversible thermal conversion to a dipyrrometheneboron difluoro-based fluorophore when exposed to a temperature at or greater than a predetermined threshold temperature. R₁-R₇ can be independently selected from: H, halogen, nitrile, isonitrile, nitroso, nitro, amine, isocyanate, carbonyl, phenyl, naphthyl, pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, ArF, ArN2, and NHCOAr where Ar is phenyl or naphthyl, C_nH_2n-1, where n is an integer from 1 to 4, CF_2n-1, C_nH₂nF_2n+1, (CF_2n+1)CO, CO₂C₂F_2n-1 , (CH₂)_nF, (CH₂)_nC1, (CH₂)_nBr, (CH₂)„I, (CH₂)_nCN, (CH₂)_nNC, (CH₂)_nNO₂, (CH₂)nNO, (CH₂)nCO(CnF2_n-1), (CH2)nCO₂H, and (CH₂)nNH₂, where n is an integer from 1 to 3, SO₃M and CO₂M where M is Na or K, cyclic alkyl groups having the formula C_nH_2n-1 where n is an integer from 4 to 6, C_nH_2n-2 and olefin derivatives having the formula C_nH_2n-1 where n is an integer from 2 to 4, RCO, CO₂R, CONHR, CON(R)₂, NHR, N(R)2, NHCOR, C(NOR)R, SO3R, SO2R, PO3R, (CH₂)nCOR, (CH₂)nS0₃R, (CH₂)_nS02R, (CH₂)_nNHR, (CH₂)_nN(R)₂, and (CH₂)_nNHCOR where R=C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4, (CH₂)_nAr, (CH₂)_nArN₂, and (CH₂)_nNHCOAr where Ar= phenyl or naphthyl and n is an integer from 1 to 4, (CH₂)_nHET where HET is pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, or isothiazolyl and n is an integer from 1 to 3, and (CH₂)_nS0₃M where M is Na or K and n is an integer from 1 to 4 alone or in combination; and R₈ can be C. R₁, R4, R₅ and R6 can all be C_nH_2n-1, where n is an integer from 1 to 4, R₂, R₃, and R₇ are H, and R8 can be C. The ODB dye can have the structure of Formula (II):

wherein at least one X is fluorine. The predetermined threshold temperature can be selected from the group consisting of about -18 °C, about -10 °C, about 1 °C, about 4 °C, or about 10 °C. The first reservoir can be a gelled matrix. The gelled matrix can include an organogel or a biopolymer gel forming material selected from the group consisting of polysaccharides, proteins, and combinations thereof. The gelled matrix can include gelatin. The ODB dye can be dissolved in a polar solvent selected from the group consisting of polar aprotic solvents, polar protic solvents, and combinations thereof. The polar aprotic solvent can be acetonitrile, acetone, cyclohexanone, DMSO, methyl ethyl ketone, methyl tert-butyl ether, diethyl ether, dimethyl ether, methyl acetate, ethyl acetate, or nitromethane and the polar protic solvent is water, glycol, methanol, ethanol, ethylene glycol, n-propanol, isopropanol, n-butanol, or isobutanol. The TTI can further include an adhesive layer. The adhesive layer can be a pressure-sensitive adhesive layer.

[0007] In another aspect, the present disclosure features a method of detecting temperature abuse, comprising: (a) positioning a TTI on or near a product in need of temperature monitoring, wherein the TTI comprises a first reservoir containing an oxadiazaborinine (ODB) dye represented by formula (I):

wherein each of R₁ through R₇ are independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and each X is halogen; wherein the ODB dye exhibits irreversible thermal conversion to a dipyrrometheneboron difluoro-based fluorophore when exposed to a temperature at or greater than a predetermined threshold temperature; (b) recording an initial color or fluorescence of the TTI; and (c) determining the color or fluorescence of the TTI during storage or transport of the product and comparing the determined color or fluorescence to the initial color or fluorescence, whereby a change in color or fluorescence indicates the product was exposed to a temperature at or above the predetermined threshold temperature during storage or transport. The product in need of temperature monitoring can be a food product, a chemical product, a pharmaceutical product, a cosmetic product or a biological material. The determining step can include visual examination, spectrophotometry, colorimetry, or photo analysis. R₁-R₇ can be independently selected from: H, halogen, nitrile, isonitrile, nitroso, nitro, amine, isocyanate, carbonyl, phenyl, naphthyl, pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, ArF, ArN₂, and NHCOAr where Ar is phenyl or naphthyl, C_nH_2n-1, where n is an integer from 1 to 4, CF_2n-1, C_nH2nF2n+1, (CF_2n+1)CO, CO2C2F_2n-1 , (CH )nF, (CH )nCl, (CH )nBr, (CH )nI, (CH )nCN, (CH )nNC, (CH₂)_nNO₂, (CH₂)_nNO, (CH₂)_nCO(C_nF_2n-1), (CH₂)_nCO₂H, and (CH₂)_nNO₂, where n is an integer from 1 to 3, SO₃M and CO₂M where M is Na or K, cyclic alkyl groups having the formula C_nH_2n-1 where n is an integer from 4 to 6, C_nH_2n-2 and olefin derivatives having the formula C_nH_2n-1 where n is an integer from 2 to 4, RCO, CO₂R, CONHR, CON(R)₂, NHR, N(R)₂, NHCOR, C(NOR)R, SO₃R, SO2R, PO3R, (CH₂)_nCOR, (CH₂)nS0₃R, (CH2)nSO₂R, (CH₂)_nNHR, (CH2)_nN(R)2, and (CH2)_nNHCOR where R=C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4, (CH2)_nAr, (CH2)_nArN2, and (CH2)_nNHCOAr where Ar= phenyl or naphthyl and n is an integer from 1 to 4, (CH₂)_nHET where HET is pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, or isothiazolyl and n is an integer from 1 to 3, and (CH₂)_nS0₃M where M is Na or K and n is an integer from 1 to 4 alone or in combination; and R₈ can be C. R₁, R4, R₅ and R₆ can all be C_nH_2n-1, where n is an integer from 1 to 4, R2, R₃, and R₇ are H, and R₈ can be C. The ODB dye can have the structure of Formula (II):

[0008] The details of one or more examples are set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0009] This written disclosure describes illustrative embodiments that are non limiting and non-exhaustive. In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0010] Reference is made to illustrative embodiments that are depicted in the figures, in which:

[0011] FIG. 1 compared prior art thermal abuse detection concepts of nanoparticle-based approaches and thermal ring opening/closing approaches with an ODB dye according to one or more embodiments of the present disclosure.

[0012] FIGS. 2A-B provides structures and schemes according to one or more embodiments of the present disclosure. (A) shows the structures of the BODIPY core (1) along with N-acetyl BODIPY (2) and a dipyrrometheneboron difluoro-based fluorophore according to one or more embodiments of the present disclosure (3); and (B) shows synthesis of oxadiazaborinine (5) proceeding via steps a) and b).

[0013] FIGS. 3A-D shows characterizations of an ODB dye according to one or more embodiments of the present disclosure: (A) and (B) show optical features of 5 and 3, respectively; (C) shows the change in absorbance with conversion of 5 to 3 over four days at room temperature (in DMSO); and (D) shows isomerization rate of 5 at room temperature in different solvents of various polarities (hexane, toluene, EtOAc, DMSO, MeCN, EtOH and Glycol). [0014] FIGS. 4A-B show solvent dependent transformation of ODB 5 to N-Ac BODIPY 3 (at room temperature) in: (A) DMSO, Ethyl acetate, hexane, and MeCN and (B) toluene, ethanol, and ethylene glycol.

[0015] FIGS. 5A-B show: (A) the ab initio calculated isomerization pathway of an ODB dye according to one or more embodiments of the present disclosure (5 to 3); and (B) ¹⁹F NMR analysis of the isomerization of 5 to 3 at 75 °C over 45 minutes, where (1) is the spectrum prior to heating (at RT), (2) time to reach 75 °C in the NMR instrument (16 min), (3) at 75 °C for 5 min, (4) at 75 °C for 15 min, (5) at 75 °C for 30 min, and (6) at 75 °C for 45 min.

[0016] FIGS. 6A-D show: (A) the thermal conversion pathways of an ODB dye according to one or more embodiments of the present disclosure (5), in polar and protic solvents; (B) color photographs of 5 and 3 before and after heating for 30 min (22 °C and 40 °C, respectively) and the results of pixel analysis of the colorimetric detection; (C) the RGB color pixel values for the thermal conversion of 5, and (D) “TTI sticks”, according to one or more embodiments of the present disclosure, containing 5 in 5% gelatin/water to detect thermal abuse under UV (excitation l = 366 nm) after exposure to various temperatures (- 20 °C to 40 °C) for the durations indicated (1 hour to 45 days).

[0017] FIG. 7 shows variable temperature ¹ H NMR spectra (400 MHz, in DMSO-de) for the thermal conversion ODB to N-Ac-BODIPY in 60 minutes: spectrum 1: prior to heating (at r.t), 2: time to reach 75 °C in the NMR instrument (15 min); then, at 75 °C for 5 min (3), 15 min (4), 30 min (5), and 45 min (6)). During the reaction time, only signals related to ODB and N-Ac-BODIPY were observed, indicating that no stable intermediates or side reaction were formed.

[0018] FIG. 8 shows full width of variable temperature ¹⁹F-NMR spectra (376 MHz, DMSO-de) of the thermal conversion ODB to N-Ac-BODIPY in 60 minutes: spectrum 1: prior to heating (at r.t), 2: time to reach 75 °C in the NMR instrument (15 min); then, at 75 °C for 5 min (3), 15 min (4), 30 min (5), and 45 min (6)).

[0019] FIGS. 9A-B show determination of ODB 5 to N-Ac BODIPY 3 (3:5) ratio (A) and rate of conversion (B).

[0020] FIGS. 10A-B show (A) conversion of ODB 5 in polar aprotic DMSO, apolar toluene and 5 % DMSO/water solution at room temperature (0, 1, 2, 3, and 4 days), 50 °C and 75 °C (0, 15, 30 and 60 min); and (B) UV-vis spectrum of Aminobispyromethen (7), obtained by hydrolysis of N-acetyl dipyrromethene (4a) (in water /pH 6.5).

DETAILED DESCRIPTION

[0021] The present disclosure describes a class of dyes, oxadiazaborinines (ODBs), that exhibit an irreversible color change or change in fluorescence when exposed to a temperature at or greater than a predetermined threshold temperature. For example, an ODB dye as described herein can indicate the dye solution, or a composition comprising the dye solution, has warmed from a frozen state to 4 °C and above. The converted compounds remain stable even when the temperature is further increased. The induced change can be used to indicate a rise in temperature, and the ODB are therefore highly useful for identifying temperature changes as TTIs.

Definitions

[0022] The terms recited below have been defined as described below. All other terms and phrases in this disclosure shall be construed according to their ordinary meaning as understood by one of skill in the art.

[0023] As used herein, “cold chain” refers to the uninterrupted temperature- controlled transport and storage system of frozen/refrigerated goods between upstream suppliers and consumers to maintain the quality and safety of the products (e.g., food, biologic, or pharmaceutical).

[0024] As used herein, “oxadiazaborinines” (or ODBs) refers to a class of organic dyes represented by Formula (I) below:

wherein each of R₁ through R₇ are independently selected from the group consisting of: hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and X is a halogen.

[0025] As used herein, “temperature abuse” refers to an unacceptable deviation from the optimal temperature or optimal temperature regime for a given product (e.g., food, biologic, or pharmaceutical) for a certain period of time.

A. OXADIAZAB ORININE DYES

[0026] Embodiments of the present disclosure describe oxadiazaborinines (ODBs) exhibiting an irreversible conversion to a dipyrrometheneboron difluoro-based chromophore or fluorophore when exposed to a temperature at or above a predetermined threshold temperature. Accordingly, the ODBs of the present disclosure can be used to indicate that an ambient temperature has risen to or above a predetermined higher threshold temperature. ODBs of the present disclosure can be represented by Formula (I) below:

wherein each of R₁ through R₇ are independently selected from the group consisting of: hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and X is a halogen. In one or more embodiments of the present disclosure, each of R₁ through R₇ can be independently selected from the group consisting of: H, F, Cl, Br, I, CN, NC, NO, NO₂, NH₂, NCO, CO2H, CONH₂, phenyl, naphthyl, pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, ArF, ArN₂, and NHCOAr where Ar is phenyl or naphthyl, C_nH_2n-1, where n is an integer from 1 to 4,

CF_2n-1, CnH_2nF_2n+1, (CF_2n+1)CO, C02C₂F_2n-1, (CH₂)nF, (CH₂)nCl, (CH₂)nBr, (CH₂)nI, (CH₂)nCN, (CH₂)nNC, (CH₂)_nNO₂, (CH₂)nNO, (CH₂)nCO(CnF_2n-1), (CH2)nCO₂H, and (CH2)_nNH2, where n is an integer from 1 to 3,

SO₃M and CO₂M where M is Na or K, cyclic alkyl groups having the formula C_nH_2n-1 where n is an integer from 4 to 6, C_nH_2n-2 and olefin derivatives having the formula C_nH_2n-1 where n is an integer from 2 to

4,

RCO, CO2R, CONHR, CON(R)2, NHR, N(R)₂, NHCOR, C(NOR)R, SO3R, SO2R, PO3R, (CH₂)nCOR, (CH₂)_nSO₃R, (CH₂)_nSO₂R, (CH₂)_nNHR, (CH₂)nN(R)2, and (CH₂)_nNHCOR where R=C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4,

(CH₂)_nAr, (CH₂)_nArN2, and (CH₂)_nNHCOAr where Ar=phenyl or naphthyl and n is an integer from 1 to 4,

(CH₂)_nHET where HET is pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, or isothiazolyl and n is an integer from 1 to 3, and

(CH₂)_nS0₃M where M is Na or K and n is an integer from 1 to 4 alone or in combination; and R₈ can be C.

[0027] Sometimes, R₁, R₂, R₃, R₄, R₅, R₆ and R₇ are selected from the group consisting of hydrogen, halogen, and alkyl, cycloalkyl, aryl, arylalkyl, acyl, or sulfo groups, alone or in combination.

[0028] In some cases, R₁, R₄, R₅ and R₆ are all lower t-alkyl or n-alkyl (e.g., methyl or ethyl), R₂, R₃, and R₇ are H, R₈ is C, and each X is a halogen, optionally at least one X is fluorine. For example, an ODB dye of the present disclosure can have the structure of Formula (II):

The non-fluorescent ODB of Formula (II) undergoes temperature-dependent conversion to a dipyrrometheneboron difluoro-based fluorophore (N-Ac-BODIPY) in polar solvents (Example).

B. OXADIAZAB ORININE DYE SYNTHESIS

[0029] Embodiments of the present disclosure describe methods of synthesizing an ODB dye. The general method includes providing a suitable dipyrromethene. As indicated by formula (I) above, a suitable dipyrromethene will include a carbonyl containing group positioned for BF2 chelation via the O and the closest N. The dipyrrolmethene can be synthesized from a suitable pyrrole by several methods. For example, a pyrrole with one alpha-position substitution and the other free can be reacted with an aromatic aldehyde in the presence of a catalytic amount of trifluoroacetic acid. The product can be oxidized to dipyrromethene using a quinone oxidant such as 2,3-Dichloro-5,6-dicyano-l,4- benzoquinone (DDQ) or p-chloranil. Alternatively, dipyrromethenes can be prepared by treating a pyrrole with an activated carboxylic acid derivative, such as an acyl chloride. Unsymmetrical dipyrromethenes can be obtained by condensing pyrroles with 2- acylpyrroles. The incorporation of BF2 is performed by condensation with borontrifluoride or a complex of boron trifluoride such as its etherate in the presence of a base. Suitable bases include but are not limited to trimethylamine, triethylamine, diisopropylethylamine, tetramethylethylenediamine, and diazobicycloundecene, at relatively low temperature (e.g., about 0 °C) to favor chelation to BF2 via the O and closest N atom thereby forming a six- membered ring, as shown in Formula (I). ODB products may be modified in a subsequent reaction by chemical techniques known to one skilled in the art including but not limited to sulfonation, nitration, alkylation, acylation, and halogenation. [0030] For example, synthesis of the ODB according to Formula II can follow Scheme 1.

SCHEME 1:

, wherein TFA is Trifluoroacetic acid, 4a is N-acetyl dipyrromethene, DCM is Dichloromethane, 3 N-Ac-BODIPY and 5 is an ODB according to Formula (II). Sometimes, synthesis of the ODB according to Formula (II) can include preparing N-acetyl dipyrromethene by heating 1H-2, 3-dimethyl pyrrole in the presence of sodium nitrite, water and acetic anhydride at 50 °C for 4 h. The BF2 can be incorporated using 7 eq. of BF₃0Et₂ and 4 eq. of NEt3 at 0 °C for 45 min.

C. TIME-TEMPERATURE INDICATORS (TTIs)

[0031] Embodiments of the present disclosure include articles and devices for use as TTIs. For example, a TTI described herein can be used to indicate that an ambient temperature or product temperature has risen to or above a predetermined threshold temperature. In some cases, a TTI described herein can be used to indicate that a product has been stored for a time period equal to or exceeding a predetermined duration. The color or fluorescence change shows when a product has been exposed to warmer temperatures and the rate of change can be used to indicate the duration of the exposure. The TTIs of the present invention can provide cost effective temperature monitoring, facilitate the identification of temperature fluctuations to reduce waste by improving temperature management in cold chains, assist with regulatory compliance for cold-chain management, and provide useful information for retailers and consumers regarding temperature history and its implications for the safety and quality of the frozen or refrigerated product.

[0032] In general, the present disclosure describes TTIs including a quantity of ODB dye represented by Formula I contained in a first reservoir. In one or more embodiments, the first reservoir comprises a gelled matrix. The ODB dye can be dispersed uniformly throughout the gelled matrix. [0033] The gelled matrix can include a suitable TTI solvent for the ODB dye. A suitable TTI solvent can be a solvent that permits conversion of the ODB to the dipyrrometheneboron difluoro-based chromophore or fluorophore when the TTI is exposed to an ambient temperature at or exceeding a predetermined temperature. In one or more embodiments described herein a suitable solvent is a polar solvent such as polar aprotic solvents, polar protic solvents, and combinations thereof. In some cases, the polar aprotic solvent can be acetonitrile, acetone, cyclohexanone, DMSO, methyl ethyl ketone, methyl tert-butyl ether, diethyl ether, dimethyl ether, methyl acetate, ethyl acetate, or nitromethane and the polar protic solvent can be selected from the group consisting of water, glycol, methanol, ethanol, ethylene glycol, n-propanol, isopropanol, n-butanol, and isobutanol. [0034] The rate of conversion of a given ODB dye can be manipulated by the number of hydrogen bond donors and acceptors in the solvent. Accordingly, the predetermined threshold temperature of the TTI can be optimized by selection of the ODB dye, as defined by R₁-R₈, the gelled matrix material (e.g., whether it creates a semi-solid environment), and the TTI solvent. For example, predetermined temperature at which the conversion of the ODB dye to the dipyrromethene, boron difluoro-based chromophore or fluorophore can be selected to show temperature abuse for a frozen stored product (e.g., about -18 °C), a stored biological material (e.g., blood) (about -10 °C), a cold-chilled product (e.g., fresh fish) (about 1 °C), a medium-chilled product (e.g., butchered meats or a vaccine) (about 4 °C), or a mild-chilled product (e.g., vegetables) (about 10 °C).

[0035] The gelled matrix can include a gel forming material selected from gel forming biopolymers, including polysaccharides, proteins, and combinations thereof. The rigidity or strength of the gel depends upon concentration of the gel forming material, the intrinsic strength of the gel forming material, which is related to the structure and molecular mass of the gel forming material, as well as the pH, temperature, and the presence of any additives. In some cases, the TTI is a substantially rigid gel. Alternatively, the gelled matrix can be less rigid and supported by an external support. The gel forming material is typically used in an amount between about 0.1% and about 10% by weight of the gelled matrix. Examples of suitable polysaccharides include agar, locust bean gum, xanthan gum, gellan gum, an alkali metal salt of alginic acid, e.g., sodium alginate or potassium alginate; an alkaline earth metal salt of alginic acid, e.g., calcium alginate or magnesium alginate; and/or carrageenan. Exemplary proteins include gelatin (e.g., 30-500 Bloom gelatin, Type A or Type B gelatin).

[0036] The gelled matrix TTIs can have a relatively high water content. For example, in one embodiment, water is present in a weight percent amount of about 70% to about 99% of the gel article. In another embodiment, the water is present in a weight percent amount of about 80% to about 98% of the gel article. In yet another embodiment, the water is present in a weight percent amount of about 90% to about 95% of the gel article. In one embodiment, the water is mixed with another liquid or solvent (e.g., a suitable solvent as described above).

[0037] In other embodiments, the gelled matrix TTI includes a biodegradable organogel comprising an organic hydrophobic solvent, and a biodegradable organogelling material, such as glutamate-based or alanine -based organogel materials.

[0038] In some embodiments of the present disclosure the gelled matrix TTI is provided as a kit comprising each component separately packaged, to be assembled before use. For example, a gelled matrix TTI kit can include a container with a quantity of ODB dye (e.g., a vial), a container with a quantity of gel forming material (e.g., a packet), a container with a quantity of TTI solvent (a bottle), and instructions for forming the gelled matrix TTI, e.g., combining the appropriate amount of gel forming material with water and heating to form a pourable matrix composition, allowing the matrix composition to cool below the predetermined threshold temperature, dissolving the ODB dye in the TTI solvent, incorporating the ODB solution into the gel forming composition, and shaping the gelled matrix TTI as desired. In some cases, the kit can include a mold for shaping the gelled matrix TTI.

[0039] The gelled matrix TTI can have any suitable shape. The gelled matrix TTIs maybe shaped by various methods such as by cutting, casting, extrusion or the like. The size of the article can be configured for the product or environment that is being monitored for temperature abuse, or configured for optimal detection, by eye or colorimetric analysis. In one or more embodiments, a rigid gel TTI article is in the form of a sheet, film, disk, cylinder, or bead, with thicknesses in the range from about 500 to about 5000 microns. The TTI article can include an outer protective layer to provide a barrier between the gelled matrix and the environment. Where the gel is less rigid, the shape can be controlled by an external support, such as a backing layer or substrate, or sealed pouch. The protective layer or pouch can be made of a biodegradable polymer film, a portion of which is preferably transparent permitting the color change to be observed through the film, and/or sufficiently translucent to allow UV light to excite the fluorophore, and permit detection of fluorescence.

[0040] In some cases, the TTI includes a means for mounting the device on an object. For example, the TTI can include an adhesive layer such as a pressure sensitive adhesive for adhering the TTI to the packaging of the product to be monitored. The adhesive layer is positioned on the base opposing the viewing window. It is advantageous for the TTI to be placed on each product (e.g., unit of sale) so that continuous monitoring is carried out from the time of packing until the time of use. A suitable pressure sensitive adhesive will exhibit good adhesion to low-energy surfaces such as polyethylene, polypropylene, vinyl chloride/vinylidene chloride copolymers, waxed paper, polymers containing surfactants which may migrate to the surface, and other low energy surfaces in materials commonly used for food or biomaterial packaging.

[0041] In some embodiments, a TTI comprises quantity of ODB dye contained in a first reservoir, as a dry powder or as a dye solution with a suitable TTI solvent as described above, wherein the first reservoir is mounted on or defined by a base layer. In one or more cases, the TTI includes an upper layer provided with a viewing window positioned over the first reservoir, configured to permit monitoring of the color and/or fluorescence of the dye solution. For example, the viewing window can be configured so that a change in color or fluorescence is visible or detectable when the ambient temperature rises above a predetermined temperature. IN some cases, the upper layer can be opaque but define a transparent viewing window enabling an observer to see through upper layer into the first reservoir. The viewing window can have any desired shape or configuration. The size of the TTI can be configured for the product or environment that is being monitored for temperature abuse, or configured for optimal detection, by eye, colorimetric, or fluorometric analysis. For example, the size of the viewing window can be based upon the limits of spectrophotometer or camera.

[0042] In one or more embodiments, the TTI has a second reservoir with a quantity of suitable solvent contained in the second reservoir or a quantity of the dipyrrometheneboron difluoro-based chromophore or fluorophore to which the ODB dye in the first reservoir is capable of converting. In the former embodiments, the second reservoir can be operably connected to the first reservoir in a configuration that permits the solvent to be mixed with the ODB dye on demand, such as immediately before being affixed to product packaging. A removable barrier member can be interposed between the first reservoir and the second reservoir. The barrier member is impervious to the solvent and rupture or removal of the barrier member permits dissolution of the ODB dye, and thereby renders the compound temperature-sensitive. In the second embodiments, the first and second reservoirs are not in fluid connection, but both are viewable through the upper layer by size of shape of the viewing window or the presence of a second viewing window over the second reservoir. The color and/or fluorescence of the second reservoir solution provides a positive control for comparison with the color and/or fluorescence observable or detectable in the first reservoir.

[0043] In one or more embodiments, the TTI is provided with a guide for interpreting the extent of the color and/or fluorescence change. For example, the guide can provide the ODB dye solution color and fluorescence, the dipyrrometheneboron difluoro-based chromophore or fluorophore solution color and fluorescence and a means for evaluating the history of the product based on the ratios of ODB and dipyrrometheneboron difluoro-based chromophore or fluorophore. For example, an observed color can be used to estimate the remaining lifetime for a product stored within a specified temperature range based on the rate of conversion. In the case of previously frozen raw seafood, poultry or meat, the product can be stored at a stable temperature at or slightly above the threshold temperature, and the retailer or consumer can rely upon the color as an indication that the ODB dye conversion is not complete, and therefore the product is safe to sell and use; whereas the color indicative of complete conversion would indicate the safe storage period has elapsed. Sometimes, a change in color indicates that the product was stored above critical temperature for a specific time, such as more than 2 hours, and the consumer can decide whether that product is safe to use when there is evidence that it has been stored above the critical temperature for that duration. The presence or absence of reservoir dye can itself be an indicator. For example, storage at 0 °C for multiple months can result in the reservoir dye being used up before the end of the product lifetime. [0044] As described above, it is advantageous for the TTI to be placed on each product (e.g., unit of sale) so that continuous monitoring is carried out from the time of packing until the time of use. In some cases, the TTI can include an adhesive layer such as a pressure sensitive adhesive described above for adhering the TTI to the packaging of the product to be monitored. The adhesive layer is positioned on the base opposing the viewing window.

D. MONITORING THE TIME-TEMPERATURE HISTORY OF A PRODUCT [0045] Embodiments of the present disclosure further include a method for monitoring the time-temperature history of a product to detect temperature abuse. In general, the method includes positioning a TTI as described above on or near a product in need of temperature monitoring, determining the initial color or temperature of the positioned TTI, and determining whether there has been a change in the color or fluorescence of the TTI during storage or transport of the product. The change in color or fluorescence indicates that the ambient temperature rose or has risen to a temperature at or about a predetermined temperature. In contrast, the TTI is stable below the critical temperature for long periods of time. For example, a TTI having a critical temperature of around -4 °C would not exhibit a color change when stored at -20 °C for about 180 days or longer. Thus, the absence of a color change indicates the product has been stored below the threshold temperature during transport and storage. Sometimes, the TTI provides information about duration of storage at a specific temperature. For example, temperatures above the critical temperature (e.g., 0 °C) will induce color change over time. Where the temperature was fixed, the storage time can be determined.

[0046] The product in need of monitoring can be a food product, a chemical product, a pharmaceutical product, a cosmetic product or a biological material. The product can be a frozen product or a chilled product. The TTI can be integrated into the packaging of the product. The predetermined temperature can be about -18 °C, to show temperature abuse for a frozen stored product, about -10 °C to show temperature abuse of a stored biological material (e.g., blood), about 1 °C to show temperature abuse of a cold-chilled product (e.g., fresh fish), about 4 °C to show temperature abuse of a medium-chilled product (e.g., butchered meats), or about 10 °C to show temperature abuse of mild-chilled product (e.g., vegetables).

[0047] The initial color or fluorescence and the change indicative of a temperature rise can be determined by eye, spectrophotometer, colorimeter or apparatus for photo analysis (e.g., camera image analysis). Cameras are typically inexpensive when compared to a colorimeter or spectrophotometer. Cameras capture light in semiconductors in photodiodes which are set up to measure light intensity and correspond to a specific pixel. The resulting image will typically be in the RGB color space. Thus, the RGB model, assigning an intensity value to each pixel, can be used to determine whether any change from the initial color has occurred. Photo analysis can be performed at one or more locations in the supply chain to determine whether the product has been exposed to thermal abuse. For example, photo images can be collected using handheld devices, such as cellphones, by delivery personnel to demonstrate integrity of the cold-chain at the time of delivery.

[0048] The ambient temperature can be the temperature encountered at any point of the cold chain. For food products, temperature control problems can occur during the storage of refrigerated food at the retailer, such as uneven temperature distribution on the shelves, and during transport. For a biological material such as a blood product, the ambient temperature can be the storage temperature at the blood bank, hospital refrigerator, or transport bags.

EXAMPLE

[0049] The following Examples are intended to illustrate the above invention and should not be construed as to narrow its scope. One skilled in the art will readily recognize that numerous variations and modifications may be made while remaining within the scope of the invention.

[0050] Temperature control is a crucial parameter for maintaining the quality of perishable frozen products, including foods and pharmaceuticals. In the distribution chain, temporary increases in temperature may occur that will adversely affect the quality of the frozen products. The detection of these incidents, classified as ‘temperature abuse’, is of great concern for the end-consumer as well as other stakeholders. In the present example, the incorporation of visual indicators that display temperature abuse into the packaging can provide a marker. Intelligent (smart) packaging aims to provide such information by using materials that show the thermal fluctuation history of the products in the distribution chain, known as time-temperature indicators (TTIs). Organic materials should be considered for TTIs. Previously, Au and Ag nanoparticles embedded in bio-polymers and other matrices have been explored for TTI applications. In these cases, the morphology of the nanoparticles was altered by temperature changes, leading to visible changes in their color (FIG. 1). However, due to the high cost of the materials and preparation, their widespread use is substantially limited. In recent years, the thermal conversion of merocyanine to spiropyran (OnVu®, a commercialized photochromic TTI), temperature-dependent diffusion of dye in mixed viscous solvents (e.g., as commercialized under the tradenames Thermo Trace TTI, ColdChain iToken, Monitor Mark™) and dye aggregation- disaggregation in polymers have been studied. Merocyanines convert to colorless spiropyrans upon warming, thereby indicating temperature changes. However, their photostability under visible light is limited. Furthermore, a disadvantage of these dyes is that the conversion is not irreversible as formed spiropyran can be reverted to the merocyanine by using UV light (>300 nm). In the diffusion-based methods, viscous liquids are mixed with dyes and applied as a small drop on the tip of blotting paper. The dye in the solvent moves along the paper through capillary action at a viscosity-dependent flow rate. As the temperature increases, the viscosity decreases, and the flow rate of (dye)-liquid on the paper accelerates. However, due to the constant flow rate, even at low temperature, ascertaining whether the product has undergone temperature abuse for critical periods of time is not possible. Therm ochromic materials, which undergo color changes with temperature, exhibit full reversibility upon cooling and hence are not suitable for TTIs. Dyes noncovalently embedded in polymers, in which dye aggregation-disaggregation interactions (e.g., based on oligo(p-phenylene vinylene) (OPV), perylene diimides) can cause a color change, are also reversible when reaggregation occurs upon cooling; thus, the detection of previous instances of temperature abuse is not possible with such materials. The polymerization of diacetylene-based materials has been explored for TTIs because this process leads to the formation of materials with various colors; however, this polymerization also occurs upon exposure to ultraviolet light in addition to temperature increases. For the above reasons, novel irreversibly convertible organic materials are needed as temperature abuse indicators.

[0051] A colorimetric approach is of great interest for practical TTI applications because of its simplicity for the end-consumer. However, it appears that a dye with an irreversible color change upon temperature abuse has not been reported to date. As a kinetically stable nonfluorescent chromophore that irreversibly converts to a bright fluorophore along with a color change could be an effective marker for TTI, the present example describes design of a thermally convertible small molecule dye, oxadiazaborinine (ODB), and exploration of its potential in TTI.

[0052] Accordingly, the present example details the design of a chromophore, its conversion under temperature abuse and a potential practical application as a TTI. Referring to the Scheme shown in FIG. 2, the molecular design was based on the well- known chromophore BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (1), which consists of a dipyrromethene ligand chelating a BF2 moiety via its two N atoms, and was guided by research on 5-N-acetylated BODIPY (N-Ac BODIPY) (2). Since amide-imidic acid tautomerism is known in organic chemistry, the design of ODB was based on the presumption that in situ formation of imidic acid (4) and its chelation to BF2 (via the O and closest N atom of dipyrromethene) would form a six-membered ring, providing ODB (5). Under thermal conditions, the intramolecular conversion may form the corresponding N,N- chelated six-membered ring containing N-acetylated BODIPY (3) driven by enthalpic effects, and this cyclization would be accompanied by a change in color and fluorescence, making this system suitable for TTI.

TABLE 1: Optimization of oxadiazaborinine synthesis

TABLE 2: Reaction optimization of dippyromethene condensation and ODB complex formation

[0053] The chelator, N-acetyl dipyrromethene 4, was synthesized by heating 1H-2,3- dimethyl pyrrole in the presence of sodium nitrite, water and acetic anhydride at 50 °C for 4 h (see FIG. 2B). The obtained mixture was purified, and 9% of the N-acetyl dipyrromethene (4_a) was isolated. The incorporation of BF2 into 4a/4i was explored at different temperatures (see Tables 1 and 2) using 7 eq. of BF₃OEt₂ and 4 eq. of NEt3. The reaction at 0 °C for 45 min gave ODB 5 as a nonfluorescent orange product in 59% yield along with 10% of magenta N-Ac-BODIPY (3). Compounds 5 and 3 were characterized by UV-vis and ¹⁹F-, ¹ H-, and ¹³C-NMR spectroscopy and ESI-MS. The structure of ODB was further confirmed by single-crystal X-ray crystallography. The measured bond lengths of B-0 (1.475 A) and B-N (1.528 A) were similar to those of cyclic O-B-N complexes, (B-O: 1.478 A) and BODIPY (1) (B-N: 1.545 A), respectively.

[0054] Optical analysis of 5 showed an absorption maximum at 507 nm (FIG. 3A) without any detectable fluorescence emission. In contrast, 3 showed a sharp absorption (l_Max = 533 nm) and intense fluorescence emission (maximum at 540 nm, f = 81%, t = 5.3 ns, in ethanol) (FIG. 3B). Consequently, the conversion of ODB 5 to BODIPY 3 was investigated in different solvents at room temperature. The conversion was fastest in polar, aprotic solvents (DMSO > MeCN > ethyl acetate), but compound 5 was stable in nonpolar solvents such as hexane and toluene. Increasing the number of hydrogen bond donors lead to a slower conversion (EtOH > ethylene glycol). Furthermore, heating 5 at 75 °C resulted significant acceleration of the conversion in DMSO (full conversion to 3 in 60 min), while no change was observed in toluene based on the absorption spectra (FIGS. 4A-B). Additionally, irradiation using different light sources at room temperature (high-powered blue or green LEDs, UV 366 nm, and white light) in various solvents resulted in no changes in the absorption spectra, which excludes the possibility of a light-mediated conversion. The ¹⁹F NMR signal of 5 in CDCl3 showed a multiplet at d = -128.3 ppm, which was significantly different from that in DMSO-d₆ (a broad singlet (s) at d = -131.6 ppm). This indicates the dynamic nature of the chelation in DMSO compared to that in CDCI3. For 3, doublets of doublets were observed at d = -146.7 and -143.9 ppm in the spectra acquired in the above solvents, respectively. The ¹ H NMR chemical shifts of 5 showed a singlet corresponding to the acetyl -CH3 protons and a broad singlet at 11.0 ppm for the pyrrolic NH. These signals and those of other protons in DMSO-d₆ were slightly broader at room temperature, which further confirmed the dynamic nature of the interactions of 5 in polar solvents (FIG. 7). Then, the mechanistic pathway for the isomerization was studied by ab initio quantum mechanical calculations (FIG. 6A) and online high-temperature (75 °C) ¹ H and ¹⁹F NMR spectroscopy (in DMSO-de). The ab initio (MP2/6-311++G**) calculations showed that the conversion of 5 to 3 (FIG. 6A) followed a nonconcerted pathway, which agrees with the observations related to the dependence on solvent polarity and the reaction rates. The transition between 5 and 6 is denoted by a proton transfer from the pyrrole NH of 5 to the imidic acid, forming the corresponding tautomer acetyl amide in 6. Thus, the N-O- chelation to BF2 results in intermediate 6 which is energetically disfavored relative to 5 by +24.9 kcal/mol, and therefore, this chelation may be reversible. However, upon substitution of the pyrrolic-A/ with BF2, thermodynamically stable N,N-chelated product 3 could be formed, which was calculated to be 10.3 kcal/mol lower in energy than 5. The ab initio calculations were verified by online high-temperature (at 75 °C) NMR spectroscopic analysis of the isomerization process, the conversion of thermally unstable 5 to stable 3 by ¹ H and ¹⁹F NMR studies (FIG. 6B). During this conversion, the measured ¹⁹F NMR spectra (in DMSO-de) revealed no new observable, stable intermediates. Hence, computationally observed intermediate 6 is transient and is rapidly converted to 3 (FIG. 7 for ¹ H NMR spectra, and FIG. 8 for full ¹⁹F NMR spectra). The peak integration ratio of 3:5 indicated that the isomerization followed first-order kinetics (see FIGS. 9A-B). No reconversion of thermally stable 3 back to 5 was observed.

[0055] As 5 does not require preactivation by either light or other factors beyond temperature, we applied 5 as an indicator of thermal abuse. For this purpose, we solidified 5 in a gelatin matrix, (freshly prepared gelatin solidifies at RT), which greatly enhances the simplicity of its use. In addition, gelatin was chosen because it is a nontoxic, biodegradable carrier as well as being inexpensive and easy to dispose of, making it an ideal, ecologically friendly matrix. We then quantified the thermal abuse by measuring UV-vis spectra, as well as by pixel analysis of the red, green and blue values (RGB, ImageJ) of the photographic images of the dye in gelatin. Furthermore, we designed easy-to-use TTI sticks for practical tests.

[0056] The gelatin matrix (5% gelatin in water, 1 mL) was mixed with ODB 5 (100 nmol in 50 mL of DMSO),and the optical spectra were measured in a 96-well plate. Dye 3 was evaluated in the same plate as a control sample. The changes in the UV-vis intensity were recorded over 30 min. Before and after the experiments, photographs of the wells were taken for image pixel analysis (FIG. 6B). The measured absorption and fluorescence indicated that the conversion of 5 to 3 did not take place in gelatin (FIG. 6A). Instead, we observed the formation of 4 and 7, as indicated by the UV-vis spectra (FIGS. 10A-B). The same observation was also made in 10% DMSO/H₂O. Nevertheless, a visible color change is observed. The intensely orange ODB sample became strongly yellow instead of the anticipated magenta color, but the process was still controlled by temperature. The RGB image characterization of 5 showed that the initial color was made up mainly of red pixels mixed with green pixels to give RGB values of 137, 80, 2. Upon heating at 40 °C for 30 min, the RGB values changed to 150, 132, 3, which corresponds to a 65% increase in green pixels. N-Ac-BODIPY 3 showed no color changes upon heating. Further UV-vis spectroscopic analysis of 5 in water (+ 5% DMSO) showed the generation of dipyrromethene 7 and 4 during heating, proving that the gelatin has no influence on the observed phenomenon. Nevertheless, this unexpected alternative conversion pathway is still sensitive for TTI indication, as the expected isomerization of 5 to 3 and unexpected 4 resulted in a color change and fluorescence. The visible color change upon temperature increase and large increase in the green component is suitable for photograph-based RGB image analysis. Furthermore, formed dipyrromethene 4 showed a strong fluorescence under 366 nm (black light) irradiation, allowing a secondary mode of detection. As a potential applicable model for packaged frozen products, polypropylene tubes (i.d: 3 mm) filled with the prepared gelatin solution of 5 were sealed at both ends with epoxy resin. These tubes were placed at -20 °C, 4 °C, 22 °C and at 40 °C for 1 h, as well as at 4 °C and -20 °C for 3 days, and at -20 °C for 45 to 180 days (FIG. 6D). A visible increase in fluorescence under 366 nm light after storage at 22 °C and 40 °C for 1 h was observed, whereas no increase in fluorescence was observed following storage at 4 °C and -20 °C. An increase in fluorescence can be observed after storage for 3 days at 4 °C. Furthermore, the stability of 5 in gelatin during storage at -20 °C for 180 days was confirmed, as no increase in fluorescence was observed (FIG. 6D, far right image).

[0057] In conclusion, this work describes kinetically stable oxadiazaborinine 5, which can be used for detecting thermal abuse based on its color change and increase in fluorescence. The irreversible thermal isomerization of 5 to fluorescent dyes 3 and 4, the high stability of the dyes, and metal-free and environmentally friendly nature of the system are important advantages of this TTI. Compound 5 will be a useful and practical TTI probe and will be suitable for mass-market use, and these applications can be explored by integrating a smartphone-aided, photograph-based color pixel analysis application software. Additionally, due to the fluorescence under 366 nm light, a broadly used ‘black light’ (e.g., such as used for detecting counterfeit currency), is suitable for the highly sensitive detection of thermal abuse with this system. This temperature-detecting probe may also be applicable in the biomedical imaging field, such as for explorations of hyperthermia and monitoring nano-heating technologies.

[0058] ODB dyes could be used for applications and processes where a fluctuation in temperature is critical, such as cold-chain integrity and transportation of consumer products and medications such as vaccines. ODBs exhibit an irreversible color change when warned from frozen state to 4 °C and above. Light was not found to affect the conversion of the ODBs, and the new dyes remain stable even when the temperature is further increased. The ODB dyes are highly stable at -20 °C (tested for over 45 days) and give an observable change color on warming. By cooling back to -20 °C does not revert the color change to the initial color. The change in color can be detected with the naked eye, but also by computer analysis of the color pixels (e.g., using a smartphone application). Thus, automated software -based detection of thermal abuse is possible.

[0059] Other embodiments of the present disclosure are possible. Although the description above contains specific examples, these should not be construed as limiting the scope of the disclosure, but as merely providing illustrations of some of the presently preferred embodiments of this disclosure. Various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and fall within the scope of this disclosure. Various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form various embodiments. Thus, the scope of the present disclosure should not be limited by the particular disclosed examples or embodiments described above.

[0060] A first aspect of the present disclosure can be described with reference to the following clauses of which:

• Clause 1 - A oxadiazaborinine (ODB) dye represented by formula (I):

wherein each of R₁ through R₇ are independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and each X is halogen; and wherein the ODB dye exhibits an irreversible conversion to a dipyrrometheneboron difluoro-based chromophore or fluorophore when exposed to a temperature at or greater than a predetermined threshold temperature.

• Clause 2 - The OBD dye according to clause 1, wherein R1-R₇ are independently selected from:

H, halogen, nitrile, isonitrile, nitroso, nitro, amine, isocyanate, carbonyl, phenyl, naphthyl, pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, ArF, ArN2, and NHCOAr where Ar is phenyl or naphthyl, C_nH_2n-1, where n is an integer from 1 to 4,

CF_2n-1, CnH2nF2n_+l, (CF_2n+1)CO, CO₂C₂F_2n-1, (CH₂)_nF, (CH₂)_nCl, (CH₂)_nBr, (CH₂)nI, (CH₂)_nCN, (CH₂)_nNC, (CH₂)_nNO₂, (CH₂)_nNO, (CH₂)_nCO(C_nF_2n-1), (CH₂)_nCO₂H, and (CH₂)_nNH₂, where n is an integer from 1 to 3,

SO3M and CO₂M where M is Na or K, cyclic alkyl groups having the formula C_nH_2n-1 where n is an integer from 4 to 6, C_nH_2n-2 and olefins having the formula C_nH_2n-1 where n is an integer from 2 to 4, RCO, CO₂R, CONHR, CON(R)₂, NHR, N(R)₂, NHCOR, C(NOR)R, SO3R, SO₂R, PO3R, (CH₂)_nCOR, (CH₂)_nS0₃R, (CH₂)_nSO₂R, (CH₂)_nNHR, (CH₂)_nN(R)₂, and (CH₂)_nNHCOR where R=C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4,

(CH₂)_nAr, (CH₂)_nArN₂, and (CH₂)_nNHCOAr where Ar= phenyl or naphthyl and n is an integer from 1 to 4,

(CH₂)_nHET where HET is pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, or isothiazolyl and n is an integer from 1 to 3, and (CH₂)_nS0₃M where M is Na or K and n is an integer from 1 to 4 alone or in combination; and R₈ is C.

• Clause 3 - The ODB dye according to clause 1 or clause 2, wherein R₁, R4, R₅ and R₆ are all C_nH_2n-1, where n is an integer from 1 to 4, R₂, R3, and R₇ are H, and R₈ is C.

• Clause 4 - The ODB dye according to any of clauses 1-3, having the structure of Formula (II):

wherein at least one X is fluorine.

• Clause 5 - The ODB dye according to any of clauses 1-4, wherein the predetermined threshold temperature is selected from the group consisting of about -18 °C, about -10 °C, about 1 °C, about 4 °C, or about 10 °C.

[0061] A second aspect of the present disclosure can be described with reference to the following clauses of which:

• Clause 6 - A Time-Temperature Indicator (TTI) comprising a first reservoir containing an oxadiazaborinine (ODB) dye represented by formula (I):

wherein each of R₁ through R₇ are independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and each X is halogen; wherein the ODB dye exhibits irreversible thermal conversion to a dipyrrometheneboron difluoro-based fluorophore when exposed to a temperature at or greater than a predetermined threshold temperature.

• Clause 7 - The TTI according to clause 6, wherein R₁-R₇ are independently selected from:

SO3M and CO2M where M is Na or K, cyclic alkyl groups having the formula C_nH_2n-1 where n is an integer from 4 to 6, C_nH_2n-2 and olefins having the formula C_nH_2n-1 where n is an integer from 2 to 4,

RCO, CO2R, CONHR, CON(R)2, NHR, N(R)₂, NHCOR, C(NOR)R, SO3R, SO2R,

PO3R, (CH₂)nCOR, (CH₂)nS0₃R, (CH2)nSO₂R, (CH₂)_nNHR, (CH₂)nN(R)2, and (CH₂)_nNHCOR where R=C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4,

(CH₂)_nAr, (CH₂)_nArN2, and (CH2)_nNHCOAr where Ar= phenyl or naphthyl and n is an integer from 1 to 4,

(CH₂)_nHET where HET is pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, or isothiazolyl and n is an integer from 1 to 3, and (CH₂)_nS0₃M where M is Na or K and n is an integer from 1 to 4 alone or in combination; and R8 is C.

• Clause 8 - The TTI according to cause 6 or clause 7, wherein R₁, R₄, R₅ and R₆ are all C_nH_2n-1, where n is an integer from 1 to 4, R₂, R₃, and R₇ are H, and R₈ is C.

Clause 9 - The TTI according to any of clauses 6-8, wherein the ODB dye has the structure of Formula (II):

wherein at least one X is fluorine.

• Clause 10 - The TTI according to any of clauses 6-9, wherein the predetermined threshold temperature is selected from the group consisting of about -18 °C, about -10 °C, about 1 °C, about 4 °C, or about 10 °C.

• Clause 11 - The TTI according to any of clauses 6-10, wherein the first reservoir is a gelled matrix.

• Clause 12 - The TTI according to any of clauses 6-11, wherein the gelled matrix comprises an organogel or a biopolymer gel forming material selected from the group consisting of polysaccharides, proteins, and combinations thereof.

• Clause 13 - The TTI according to clause 12, wherein the gelled matrix comprises gelatin.

• Clause 14 - The TTI according to any of clauses 6-13, wherein the ODB dye is dissolved (i.e., present in dissolved form) in a polar solvent selected from the group consisting of polar aprotic solvents, polar protic solvents, and combinations thereof.

• Clause 15 - The TTI according to clause 14, wherein the polar aprotic solvent is acetonitrile, acetone, cyclohexanone, DMSO, methyl ethyl ketone, methyl tert-butyl ether, diethyl ether, dimethyl ether, methyl acetate, ethyl acetate, or nitromethane and the polar protic solvent is water, glycol, methanol, ethanol, ethylene glycol, n-propanol, isopropanol, n-butanol, isobutanol, or mixtures thereof.

• Clause 16 - The TTI according to any of clauses 6-15, wherein the TTI further comprises an adhesive layer. • Clause 17 - The TTI according to clause 16, wherein the adhesive layer is a pressure- sensitive adhesive layer.

[0062] A third aspect of the present disclosure can be described with reference to the following clauses of which:

• Clause 18 - A method of detecting temperature abuse, comprising:

(a) positioning a TTI on or near a product in need of temperature monitoring, wherein the TTI comprises a first reservoir containing an oxadiazaborinine (ODB) dye represented by formula (I):

wherein each of R₁ through R₇ are independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, aryl, arylalkyl, acyl, groups containing oxygen, groups containing nitrogen, groups containing sulfur, groups containing phosphorous, groups containing boron, and groups containing metals, alone or in combination; R₈ is selected from the group consisting of C, N, and P; and each X is halogen; wherein the ODB dye exhibits irreversible thermal conversion to a dipyrrometheneboron difluoro-based fluorophore when exposed to a temperature at or greater than a predetermined threshold temperature;

(b) recording an initial color or fluorescence of the TTI; and

(c) determining the color or fluorescence of the TTI during storage or transport of the product and comparing the determined color or fluorescence to the initial color or fluorescence, whereby a change in color or fluorescence indicates the product was exposed to a temperature at or above the predetermined threshold temperature during storage or transport. • Clause 19 - The method according to clause 18, wherein the product in need of temperature monitoring is a food product, a chemical product, a pharmaceutical product, a cosmetic product or a biological material.

• Clause 20 - The method according to clause 18 or clause 19, wherein the determining step includes visual examination, spectrophotometry, colorimetry, or photo analysis.

[0063] The scope of this disclosure should be determined by the appended claims and their legal equivalents. The present disclosure encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present disclosure, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.

[0064] The foregoing description of various preferred embodiments of the disclosure have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise embodiments, and obviously many modifications and variations are possible in light of the above teaching. The example embodiments, as described above, were chosen and described in order to best explain the principles of the disclosure and its practical application to thereby enable others skilled in the art to best utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto

[0065] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A oxadiazaborinine (ODB) dye represented by formula (I):

2. The ODB dye of claim 1, wherein R1-R₇ are independently selected from:

H, halogen, nitrile, isonitrile, nitroso, nitro, amine, isocyanate, carbonyl, phenyl, naphthyl, pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, ArF, ArN2, and NHCOAr where Ar is phenyl or naphthyl, C_nH_2n-1, where n is an integer from 1 to 4, CF_2n-1, CnH_2nF_2n+1, (CF_2n+1)CO, C02C₂F_2n-1, (CH₂)nF, (CH₂)nCl, (CH₂)nBr, (CH₂)nI, (CH₂)nCN, (CH₂)nNC, (CH₂)_nNO₂, (CH₂)nNO, (CH₂)nCO(CnF_2n-1), (CH2)_nC02H, and (CH₂)_nNH₂, where n is an integer from 1 to 3,

SO3M and CO2M where M is Na or K, cyclic alkyl groups having the formula C_nH_2n-1 where n is an integer from 4 to

6, C_nH_2n-2 and olefin derivatives having the formula C_nH_2n-1 where n is an integer from 2 to

4,

RCO, CO2R, CONHR, CON(R)2, NHR, N(R)₂, NHCOR, C(NOR)R, SO3R, SO2R, PO3R, (CH₂)nCOR, (CH₂)nS0₃R, (CH2)nSO₂R, (CH₂)_nNHR, (CH₂)nN(R)2, and (CH2)_nNHCOR where R= C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4,

(CH₂)_nAr, (CH₂)_nArN2, and (CH₂)_nNHCOAr where Ar= phenyl or naphthyl and n is an integer from 1 to 4,

(CH₂)_nHET where HET is pyrryl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, or isothiazolyl and n is an integer from 1 to 3, and (CH₂)_nS03M where M is Na or K and n is an integer from 1 to 4 alone or in combination; and

R8 is C.

3. The ODB dye of claim 1, wherein R₁, R₄, R₅ and R6 are all C_nH_2n-1, where n is an integer from 1 to 4, R₂, R₃, and R₇ are H, and R8 is C.

4. The ODB dye of claim 3, having the structure of Formula (II):

wherein at least one X is fluorine.

5. The ODB dye of claim 1, wherein the predetermined threshold temperature is selected from the group consisting of about -18 °C, about -10 °C, about 1 °C, about 4 °C, or about 10 °C.

6. A Time-Temperature Indicator (TTI) comprising a first reservoir containing an oxadiazaborinine (ODB) dye represented by formula (I):

7. The TTI of claim 6, wherein R1-R₇ are independently selected from:

CF_2n-1, CnH_2nF_2n+1, (CF_2n+1)CO, C02C F_2n-1, (CH₂)nF, (CH₂)nCl, (CH₂)nBr, (CH₂)nI, (CH₂)nCN, (CH₂)nNC, (CH₂)_nNO₂, (CH₂)nNO, (CH₂)nCO(CnF_2n-1), (CH₂)_nCO₂H, and (CH₂)_nNO₂, where n is an integer from 1 to 3,

6, C_nH₂n-2 and olefin derivatives having the formula C_nH_2n-1 where n is an integer from 2 to

4,

RCO, CO2R, CONHR, CON(R)2, NHR, N(R) , NHCOR, C(NOR)R, SO3R, SO2R, PO3R, (CH₂)nCOR, (CH₂)nS0 R, (CH2)nSO₂R, (CH₂)_nNHR, (CH₂)nN(R)2, and (CH2)_nNHCOR where R=C_nH_2n-1 and n is an integer from 1 to 4, C_nH_2n-m where n is an integer from 2 to 4 and m is an integer from 2 to 4,

8. The TTI of claim 6, wherein R₁, R₄, R₅ and R₆ are all C_nH_2n-1, where n is an integer from 1 to 4, R₂, R₃, and R₇ are H, and R₈ is C.

9. The TTI of claim 8, wherein the ODB dye has the structure of Formula (II):

wherein at least one X is fluorine.

10. The TTI of claim 6, wherein the predetermined threshold temperature is selected from the group consisting of about -18 °C, about -10 °C, about 1 °C, about 4 °C, or about 10 °C.

11. The TTI of claim 6, wherein the first reservoir is a gelled matrix.

12. The TTI of claim 11, wherein the gelled matrix comprises an organogel or a biopolymer gel forming material selected from the group consisting of polysaccharides, proteins, and combinations thereof.

13. The TTI of claim 12, wherein the gelled matrix comprises gelatin.

14. The TTI of claim 6, wherein the ODB dye is dissolved in a polar solvent selected from the group consisting of polar aprotic solvents, polar protic solvents, and combinations thereof.

15. The TTI of claim 14, wherein the polar aprotic solvent is acetonitrile, acetone, cyclohexanone, DMSO, methyl ethyl ketone, methyl tert-butyl ether, diethyl ether, dimethyl ether, methyl acetate, ethyl acetate, or nitromethane and the polar protic solvent is water, glycol, methanol, ethanol, ethylene glycol, n-propanol, isopropanol, n-butanol, or isobutanol.

16. The TTI of claim 6, wherein the TTI further comprises an adhesive layer.

17. The TTI of claim 16, wherein the adhesive layer is a pressure-sensitive adhesive layer.

18. A method of detecting temperature abuse, comprising:

(b) recording an initial color or fluorescence of the TTI; and

(c) determining the color or fluorescence of the TTI during storage or transport of the product and comparing the determined color or fluorescence to the initial color or fluorescence, whereby a change in color or fluorescence indicates the product was exposed to a temperature at or above the predetermined threshold temperature during storage or transport.

19. The method of claim 18, wherein the product in need of temperature monitoring is a food product, a chemical product, a pharmaceutical product, a cosmetic product or a biological material.

20. The method of claim 18, wherein the determining step includes visual examination, spectrophotometry, colorimetry, or photo analysis.