RELATED APPLICATION

This application is a claims the benefit of U.S. Provisional Application No. 61/210,217, filed on March 16, 2009, the entire teachings of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

With increasing concern about human safety and the exponential increase in terrorist attacks throughout the world, there is an escalating need and demand to monitor the presence of explosives in the vapor phase at lower and lower concentrations. Existing methods of detection have often proven inadequate. The current state of the art in detection technique systems include ion mobility spectrometers (IMS), electrochemical detectors, chemi-resistor based detectors, gas chromatography mass-spectroscopy (GC-MS) based techniques and microelectromechanical systems (MEMS) based sensors. IMS and GC-MS techniques typicaly are very sensitive but not field-deployable because of high cost and bulky size. The response time of these devices are very low and not suited for real time analysis. These instruments also need a trained user for handling and they lose effectiveness when the sampling environment is contaminated with inteferants. Chemi-resistor devices generally are low in cost and portable but they do not exhibit the required sensitivity and selectivity. Most chemi-resistor devices work at higher temperature (above 150 ⁰ C), which makes instrumentation relatively cumbersome. MEMS based devices show very poor selectivity. A FIDO sensor is a fluorescence quenching based sensor device. However, the operating wavelength range, which rantes from 350 nm to 450 nm, increases the instrumentation cost significantly. A major drawback of FIDO sensor is that it is unable to detect RDX and HMX which are very commonly used explosives.

Therefore, a need exists for a device and methods that overcome or minimize the above-referenced problems. SUMMARY OF THE INVENTION

In one embodiment, the present invention is a device, comprising a sensing element, a light source configured to illuminate the sensing element, a light detector configured to detect the light emitted by the sensing element. The sensing element includes a polymer or a copolymer having at least one unit of structural formula (I):

wherein R and R', for each occurrence, are independently selected from

- hydrogen,

- hydroxyl, - a C1-C12 alcohol, a Cl -C 16 carboxylic acid,

- a Cl-C16 alkyl,

- a (CO-C 12 alkoxy)-C 1 -C 12 alkyl,

- a (CO-C 12 alkoxy)-C 1 -C 12 alcohol, - a group having a structural formula -R ² -O-C(O)-NH-R ³ -CO ₂ R ⁴ ,

- a group having a structural formula -R ⁵ -O-C(O)-NH-R ⁶ -R ⁷ , a group having a structural formula -R ⁸ -O-C(O)-R ⁹ ,

- -R ^a -OC(O)NHCH ₂ -R ^b ,

- -R ^a -OC(O)NH-R ^c , - -R ^a -C(O)NH-R ^d , and

- -R ^a -C(O)O-R ^d .

In formula (I), a _^ / C~* 11- /C~* 1120 a „1lk1 y 1le ,-.„ne _^ , i R~> 4 , R ⁷ and R ⁹ are each independently a C1-C20 alkyl, each R ^a is independently absent or is a C1-C4 alkylene, each R ^b is independently -C(O)OR ⁰ , each R ^c is independently Cl -C 16 alkyl or a C6-C18 aryl or heteroaryl, and each R ^d is independently a C1-C6 alkyl, optionally substituted with poly(ethylene glycol) and poly(dimethyl siloxane).

In another embodiment, the present invention is a method of detecting a chemical compound, comprising the step of exposing a device to a chemical compound, whereby the fluorescence emitted by the sensing element is indicative of the presence of at least one chemical compound in the sample, wherein the device includes: a sensing element; a light source configured to illuminate the sensing element; and a light detector configured to detect the light emitted by the sensing element, wherein the sensing element includes a polymer or a copolymer having at least one unit of structural formula (I), described above.

In another embodiment, the present invention is a polymer comprising at least one unit represented by the structural formulas (VIII) and (IX):

In formulas (VIII) and (IX), R ^a for each occurrence is independently absent or is a C1-C4 alkylene, R ^b for each occurrence is independently -C(O)OR ⁰ , R ^c for each occurrence is independently Cl -C 16 alkyl or a C6-C18 aryl or heteroaryl, m and n are each independently an integer from 1 to 50, q and r are each independently 1 or 2, and p and s are each independently an integer from 1 to 50.

In another embodiment, the present invention is a polymer comprising at least one unit represented by the structural formulas, (X), (XI), (XII) or (XIII):

In formulas (X) through (XIII), each R" is independently C1-C20 alkyl or a C6-C18 aryl, each R ^a is independently absent or is a C1-C4 alkylene, each R ^b is independently -C(O)OR ^C , and each R ^c is independently C 1 -C 16 alkyl or a C6-C 18 aryl or heteroaryl.

The devices and methods described herein provide a number of advantages. For example, the devices of the invention are inexpensive and permit mass manufacture. Further, the materials and devices of the invention herein exhibit relatively high sensitivity, such as by detecting RDX present in amounts as low as 5 ppt.

The devices and methods disclosed herein detect RDX and HDX in the vapor phase (RDX vapor pressure 1000 times smaller than TNT, HMX' s vapor pressure is 1000 time smaller than RDX) meaning that the amount of these chemicals in any ambient atmosphere is likely to be very low.

In certain embodiments, the device comprises a sensing element that includes a 2 - 20 nm film, which is inexpensive and easy to mass produce. In other embodiments, the sensing element includes a fluorescent polymer having an absorption peak at 440 nm and emission at 600 nm, which permits the use of widely available and inexpensive optical equipment. The working wave range of 550 nm to 700 nm of a sensing element of the present invention provides yet another advantage in reducing the number of false alarms due to non-interference with the chemicals present in the environment. Further, the devices and methods of the present invention do not require pre-concentrating the compound being detected. The lack of necessity for a pre-concentration step allows vapors to be detected in few seconds or less; thereby providing a notable advancement over most the state-of-the-art detectors.

Further advantages of the devices of the present invention portability, low cost, and rapid response at low concentrations of analytes. The use of organic polymeric materials described herein permits alteration of chemical properties to suit detection needs.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.

FIG. 1 is a plot showing absorption spectra of PURET either in a THF solution or in thin film.

FIG. 2 is a plot showing fluorescence emission spectra of PURET either in solution or on thin film.

FIG. 3 is a schematic diagram of one embodiment of the device of the present invention.

FIG. 4A is a plot showing fluorescence emission spectra of a solution of PURET in THF in the presence of different concentrations of RDX. FIG. 4B is a plot showing fluorescence emission spectra of a thin film of

PURET in the presence of saturated vapor of RDX. Each curve represents a different duration of measurement, namely 0 minutes, 1, minute, 4 minutes and 8 minutes, in the order of decreasing peak intensity.

FIG. 5 is a plot showing relative intensity of fluorescence of a thin film of PURET as a function of time in the presence of the indicated analytes. FIG. 6 is a plot showing relative intensity of fluorescence of a thin film of [3- (2-ethyl-isocyanato-octa-decanyl)-thiophene (ADS518PT) as a function of time in the presence of the indicated analytes.

FIG. 7 is a plot showing relative intensity of fluorescence of thin films of [3- (2-ethyl-isocyanato-octa-decanyl)-thiophene (ADS518PT) and PURET in the presence of RDX vapor.

FIG. 8 is a plot showing relative intensity of fluorescence of a PURET thin film as a function of time in the presence of either RDX or HMX.

DETAILED DESCRIPTION OF THE INVENTION Glossary

As used herein, "alkyl" refers to a straight-chain or branched saturated hydrocarbon group. Examples of alkyl groups include methyl (Me), ethyl (Et), propyl (e.g., n-propyl, and isopropyl), butyl (e.g., n-butyl, isobutyl, s-butyl, t-butyl), pentyl groups (e.g., n-pentyl, isopentyl, neopentyl), and the like. A lower alkyl group typically has up to 6 carbon atoms. In various embodiments, an alkyl group has 1 to 6 carbon atoms, and is referred to as a "C 1-6 alkyl group." Examples of C 1-6 alkyl groups include, but are not limited to, methyl, ethyl, propyl (e.g., n-propyl and isopropyl), and butyl groups (e.g., n-butyl, isobutyl, s-butyl, t-butyl). A branched alkyl group has at least 3 carbon atoms (e.g., an isopropyl group) and up to 6 carbon atoms, e.g. it is a C3-6 alkyl group, i.e., a branched lower alkyl group. Examples of branched lower alkyl groups include, but are not limited to, isopropyl, isobutyl, sec- butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl.

As used herein, the term "alkenyl" means a saturated straight chain or branched non-cyclic hydrocarbon having from 2 to 10 carbon atoms and having at least one carbon-carbon double bond. Representative straight chain and branched C2-C10 alkenyls include vinyl, allyl, 1-butenyl, 2-butenyl, isobutylenyl, 1-pentenyl, 2-pentenyl, 3 -methyl- 1-butenyl, 2-methyl-2-butenyl, 2,3-dimethyl-2-butenyl, 1- hexenyl, 2-hexenyl, 3-hexenyl, 1-heptenyl, 2-heptenyl, 3-heptenyl, 1-octenyl, 2- octenyl, 3-octenyl, 1-nonenyl, 2-nonenyl, 3-nonenyl, 1-decenyl, 2-decenyl, 3- decenyl and the like. Alkenyl groups may be optionally substituted with one or more substituents. As used herein, the term "alkynyl" means a saturated straight chain or branched non-cyclic hydrocarbon having from 2 to 10 carbon atoms and having at lease one carbon-carbon triple bond. Representative straight chain and branched alkynyls include acetylenyl, propynyl, 1-butynyl, 2-butynyl, 1-pentynyl, 2-pentynyl, 3 -methyl- 1-butynyl, 4-pentynyl, 1-hexynyl, 2-hexynyl, 5-hexynyl, 1-heptynyl, 2- heptynyl, 6-heptynyl, 1-octynyl, 2-octynyl, 7-octynyl, 1-nonynyl, 2-nonynyl, 8- nonynyl, 1-decynyl, 2-decynyl, 9-decynyl, and the like. Alkynyl groups may be optionally substituted with one or more substituents.

As used herein, "cycloalkyl" refers to a non-aromatic carbocyclic group including cyclized alkyl, alkenyl, and alkynyl groups. A cycloalkyl group can be monocyclic (e.g., cyclohexyl) or polycyclic (e.g., containing fused, bridged, and/or spiro ring systems), wherein the carbon atoms are located inside or outside of the ring system. Any suitable ring position of the cycloalkyl group can be covalently linked to the defined chemical structure. In various embodiments, a cycloalkyl group has 3-6 carbon atoms, and is referred to as a "C3-6 cycloalkyl group."

Examples of C3-6 cycloalkyl groups include, but are not limited to, cyclopropyl, cyclopropylmethyl, cyclopropylethyl, cyclopropylpropyl, cyclobutyl, cyclobutylmethyl, cyclobutylethyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, cyclopentenyl, cyclohexenyl, and cyclohexadienyl groups, as well as their homologs, isomers, and the like.

As used here, the term "alkylene" refers to a divalent alkyl group that has two points of attachment to the rest of the compound. Non- limiting examples of alkylene groups include a divalebt C 1-6 groups such as methylene (-CH ₂ -), ethylene (-CH ₂ CH ₂ -), n-propylene (-CH ₂ CH ₂ CH ₂ -), isopropylene (-CH ₂ CH(CH ₃ )-), and the like. Alkylene groups may be optionally substituted with one or more substituents. A divalent C 1-6 alkyl group can be a straight chain or branched alkyl group, which as a linking group is capable of forming a covalent bond with two other moieties. Examples of a divalent C 1-6 alkyl group include, for example, a methylene group, an ethylene group, an ethylidene group, an n-propylene group, an isopropylene group, an isobutylene group, an s-butylene group, an n-butylene group, and a t- butylene group. As used herein, "alkoxy" refers to an -O-alkyl group wherein the alkyl group may be a straight or branched chain. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy (e.g., n-propoxy and isopropoxy), t-butoxy groups, and the like. As used herein, "non-aromatic heterocyclic group" refers to a non-aromatic cycle having 5-7 ring atoms, among which 1 to 3 ring atoms are heteroatoms independently selected from oxygen (O), nitrogen (N) and sulfur (S), and that optionally contains one or more, e.g., two, double or triple bonds. One or more N or S atoms in a non-aromatic heterocyclic group ring can be oxidized (e.g., morpholine N-oxide, thiomorpholine S- oxide, thiomorpholine S,S-dioxide). Non-aromatic heterocyclic groups can also contain one or more oxo groups, such as piperidone, oxazolidinone, pyrimidine-2,4(lH,3H)-dione, pyridin-2(lH)-one, and the like. Examples of non-aromatic heterocyclic groups include, among others, morpholine, thiomorpholine, pyran, imidazolidine, imidazoline, oxazolidine, pyrazolidine, pyrazoline, pyrrolidine, pyrroline, tetrahydrofuran, tetrahydrothiophene, piperidine, piperazine, and the like. A non-aromatic heterocyclic group can be optionally substituted.

As used herein, "aryl" refers to an aromatic monocyclic hydrocarbon ring system or a polycyclic ring system in which two or more aromatic hydrocarbon rings are fused (i.e., having a bond in common with) together or at least one aromatic monocyclic hydrocarbon ring is fused to one or more cycloalkyl and/or non- aromatic heterocyclic group rings. An aryl group can have from 6 to 14 carbon atoms in its ring system, which can include multiple fused rings. In some embodiments, a polycyclic aryl group can have from 7 to 14 carbon atoms. Any suitable ring position of the aryl group can be covalently linked to the defined chemical structure. Examples of aryl groups having only aromatic carbocyclic ring(s) include, but are not limited to, phenyl, 1-naphthyl (bicyclic), 2-naphthyl (bicyclic), anthracenyl (tricyclic), phenanthrenyl (tricyclic) and like groups. Examples of polycyclic ring systems in which at least one aromatic carbocyclic ring is fused to one or more cycloalkyl and/or non-aromatic heterocyclic group rings include, among others, benzo derivatives of cyclopentane (i.e., an indanyl group, which is a 5,6-bicyclic cycloalkyl-aromatic ring system), cyclohexane (i.e., a tetrahydronaphthyl group, which is a 6,6-bicyclic cycloalkyl-aromatic ring system), imidazoline (i.e., a benzimidazolinyl group, which is a 5,6-bicyclic non-aromatic heterocyclic group/aromatic ring system), and pyran (i.e., a chromenyl group, which is a 6,6-bicyclic non-aromatic heterocyclic group/aromatic ring system). Other examples of aryl groups include, but are not limited to, benzodioxanyl, benzodioxolyl, chromanyl, indolinyl groups, and the like. In some embodiments, aryl groups optionally contain up to three independently selected substitution groups. As used herein, "heteroaryl" or "heteroaromatic" refers to an aromatic monocyclic ring system or a polycyclic ring system where at least one of the rings present in the ring system is aromatic, containing 5-7 or 5-9 ring atoms, among which 1 to 3 ring atoms are heteroatoms independently selected from oxygen (O), nitrogen (N) and sulfur (S). Polycyclic heteroaryl groups include two or more heteroaryl rings fused together, and monocyclic heteroaryl rings fused to one or more aromatic carbocyclic rings, non-aromatic carbocyclic rings, and/or non- aromatic non-aromatic heterocyclic group rings. The heteroaryl group can be attached to the defined chemical structure at any heteroatom or carbon atom that results in a stable structure. Generally, heteroaryl rings do not contain 0-0, S-S, or S-O bonds. However, one or more N or S atoms in a heteroaryl group can be oxidized (e.g., pyridine N-oxide, thiophene S-oxide, thiophene S, S-dioxide). Examples of such heteroaryl rings include, but are not limited to, pyrrole, furan, thiophene, pyridine, pyrimidine, pyridazine, pyrazine, triazole, tetrazole, pyrazole, imidazole, isothiazole, thiazole, thiadiazole, isoxazole, oxazole, oxadiazole, indole, isoindole, benzofuran, benzothiophene, quinoline, 2-methylquinoline, isoquinoline, quinoxaline, quinazoline, benzotriazole, benzimidazole, benzothiazole, benzisothiazole, benzisoxazole, benzoxadiazole, benzoxazole, cinnoline, IH- indazole, 2H-indazole, indolizine, isobenzo furan, naphthyridine, phthalazine, pteridine, purine, oxazolopyridine, thiazolopyridine, imidazopyridine, furopyridine, thienopyridine, pyridopyrimidine, pyridopyrazine, pyridopyridazine, thienothiazole, thienoxazole, and thieno imidazole. Further examples of heteroaryl groups include, but are not limited to, 4,5,6,7-tetrahydroindole, tetrahydroquinoline, benzothienopyridine, benzofuropyridine, and the like. In some embodiments, heteroaryl groups can be substituted with up to three independently selected substituent groups. The foregoing heteroaryl groups may be C-attached or N- attached (where such is possible). For instance, a group derived from pyrrole may be pyrrol- 1-yl (N-attached) or pyrrol-3-yl (C-attached).

As used herein, the term "(hetero)aryloxy" means an "(hetero)aryl-O-" group, wherein aryl and heteroaryl are defined above. Examples of an aryloxy group include phenoxy or naphthoxy groups. Suitable substituents for any of the above defined chemical moieties, including thiophene moiety, are those that do not substantially interfere with the activity of the disclosed compound. One or more substituents can be present, which can be identical or different. Examples of such substituents include a halogen, an alkyl, an alkenyl, a cycloalkyl, a cycloalkenyl, an aryl, a heteroaryl, a haloalkyl, cyano, nitro, haloalkoxy. Further examples of suitable substituents for a substitutable carbon atom in an aryl, a heteroaryl, or a non-aromatic heterocyclic group include but are not limited to -OH, halogen (F, Cl, Br, and I), R, OR, -CH ₂ R, -CH ₂ OR, -CH ₂ CH ₂ OR. Each R is independently an alkyl group.

In some embodiments, suitable substituents for a substitutable carbon atom of any of the above defined chemical moieties include one or more halogen, hydroxyl, C1-C20 alkyl, C2-C20 alkenyl, Cl -C 12 alkoxy, aryloxy group, arylamino group and C1-C20 haloalkyl, -R ^a -OC(O)NHCH ₂ -R ^b , -R ^a -0C(0)NH-R ^c , -R ^a -C(0)NH-R ^d , or -R ^a -C(O)O-R ^d , where R ^a is absent or is a C1-C4 alkylene, R ^b is -C(O)OR ^C , R ^c is Cl -C 16 alkyl or a C6-C18 aryl or heteroaryl, and R ^d is a C1-C6 alkyl, optionally substituted with poly(ethylene glycol) and poly(dimethyl siloxane). Compounds Detectable by Devices and Methods of the Present Invention

The present invention relates to the development of a sensing element to detect chemical compounds. In certain embodiments, the chemical compounds are explosive compounds. In various embodiment, the chemical compounds are nitrogen-containing aromatic or non-aromatic compounds. In certain embodiments, the explosives contain nitroaromatics. In alternative embodiments, the explosives contain nitroamines. The device incorporating this sensing element finds broad application for detecting weapons-grade explosives.

In one embodiment, the present invention is a method for detecting explosives such as 2,4-Dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), picric acid (PA), N-methyl-N,2,4,6-tetranitroaniline (Tetryl), l,3,5-trinitro-l,3,5- triazacyclohexane (RDX), l,3,5,7-tetranitro-l,3,5,7-tetraazacyclooctane (HMX), and pentaerythritol tetranitrate (PETN).

In one embodiment, the explosives are non-aromatic heterocyclic compounds. Preferably, the compounds comprise at least one nitroamine moiety. More preferably, the compounds are PETN, RDX and/or HMX. Even more preferably, the compounds are RDX and/or HMX.

The molecules of the explosive compounds are detected using a conjugated polymer. Preferably, the conjugated polymer is a fluorescent polymer. More preferably, the polymer is a polythiophene, described below in detail. Without being limited to any particular theory, it is believed that a polymer employed by a device of the present invention exhibits fluorescence quenching mechanism to thereby detect a broad class of nitrogen-containing explosives.

Sensing Element

In one embodiment, the devices of the present invention comprise a sensing element. As used herein, the term "sensing element" refers to an element of a device that comprises a polymer (or a copolymer) that can detect a nitrogen-containing compound. Preferably, the polymer is thiophene-based. For example, the polymer can comprise at least one repeat unit of structural formula (I):

In formula (I), R and R', for each occurrence, are independently selected from - hydrogen; hydroxyl;

- a Cl-C 12 alcohol; a C1-C16 carboxylic acid;

- a Cl-C16 alkyl; - a (CO-C 12 alkoxy)-C 1 -C 12 alkyl;

- a (CO-C 12 alkoxy)-C 1 -C 12 alcohol;

- a group having a structural formula -R ² -O-C(O)-NH-R ³ -CO ₂ R ⁴ ; a group having a structural formula -R ⁵ -O-C(O)-NH-R ⁶ -R ⁷ ; a group having a structural formula -R ⁸ -O-C(O)-R ⁹ ; - -R ^a -OC(O)NHCH ₂ -R ^b ;

- -R ^a -OC(O)NH-R ^c ;

- -R ^a -C(O)NH-R ^d ; and

- -R ^a -C(O)O-R ^d . In formula (I), R ² , R ³ , R ⁵ , R ⁶ and R ⁸ are each independently a C1-C12 alkylene; and R ⁴ , R ⁷ and R ⁹ is each independently a C1-C20 alkyl. R ^a is absent or is a C1-C4 alkylene, R ^b is -C(O)OR ^C , R ^c is Cl -C 16 alkyl or a C6-C18 aryl or heteroaryl, and R ^d is a C1-C6 alkyl, optionally substituted with poly(ethylene glycol) and poly(dimethyl siloxane). Preferably, in formula (I), at least one R or R' is not hydrogen.

In a preferred embodiment, the polymer comprises at least one subunit of formula (I), wherein R' is hydrogen. Values and preferred values of the remainder of the variables are as defined above with respect to formula (I).

In another embodiment, R is a groups represented by the structural formula -R ² -O-C(O)-NH-R ³ -CO ₂ R ⁴ . Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R ² and R ³ are each independently a C1-C4 alkylene, and R ⁴ is, independently, a C1-C4 alkyl. More preferably, R ² is ethylene, and independently, R ³ is methylene, and, independently, R ⁴ is butyl. In another embodiment, R is a group having a structural formula

-R ⁵ -O-C(O)-NH-R ⁶ -R ⁷ . Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R ⁵ and R ⁶ are each independently a C1-C4 alkylene, and R ⁷ is, independently, a C6-C20 alkyl. More preferably, R ² is ethylene, and independently, R ³ is methylene, and, independently, R ⁴ is the C 15 alkyl.

In another embodiment, R is a C1-C6 carboxylic acid. Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R is a C1-C4 carboxylic acid, more preferably, -CH ₂ -COOH.

In another embodiment, R is a Cl-C 12 alkyl. Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R is a C1-C6 alkyl. More preferably, R is hexyl. In another embodiment, R is a C1-C6 alcohol. Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R is -CH ₂ OH or -CH ₂ CH ₂ OH.

In another embodiment, R is a (C0-C6 alkoxy)-Cl-C6 alkyl. Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R is a (C0-C2 alkoxy)-Cl-C6 alkyl.

In another embodiment, R is a (C0-C6 alkoxy)-Cl-C6 alcohol. Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R is a (C0-C2 alkoxy)-Cl-C6 alcohol. In another embodiment, R is a group having a structural formula

-R ⁸ -O-C(O)-R ⁹ . Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). Preferably, R ⁸ is a C1-C3 alkylene and R ⁹ is, independently, a C1-C3 alkyl.

In one embodiment the polymer comprises at least one subunit of structural formula (I), wherein R' is hydrogen, R is a group represented by the structural formula -R ² -O-C(O)-NH-R ³ -CO ₂ R ⁴ , wherein R ² is ethylene, R ³ is methylene, and R ⁴ is butyl.

In another embodiment, the polymer comprises at least one subunit of structural formula (I), wherein R' is hydrogen and R is -CH ₂ -COOH. In another embodiment, the polymer comprises at least one subunit of structural formula (I), wherein R' is hydrogen and R is hexyl.

In another embodiment, R' is hydrogen and R is a group having a structural formula -R ⁵ -O-C(O)-NH-R ⁶ -R ⁷ , wherein R ⁵ is ethylene, and independently, R ⁶ is methylene, and, independently, R ⁷ is the C 15 alkyl. In another embodiment, R' is hydrogen and R is a group having a structural formula -R ⁸ -O-C(O)-R ⁹ , wherein R ⁸ is methylene and R ⁹ is methyl.

In another embodiment, R is, for each occurrence, independently selected from -R ^a -OC(O)NHCH ₂ -R ^b , -R ^a -0C(0)NH-R ^c , -R ^a -C(O)NH-R ^d , or -R ^a -C(O)O-R ^d , where R ^a is absent or is a C1-C4 alkylene, R ^b is -C(O)OR ^C , R ^c is Cl -C 16 alkyl or a C6-C18 aryl or heteroaryl, and R ^d is a C1-C6 alkyl, optionally substituted with poly(ethylene glycol) and poly(dimethyl siloxane). Values and preferred values of the remainder of the variables are as defined above with respect to formula (I). R ^a , for each occurrence is preferably, a C1-C4 alkylene, more preferably, C1-C2 alkylene. R ^c for each occurrence, is preferably a C4-C16 alkyl or a C6-C14 aryl. R ^d for each occurrence, is preferably a C1-C2 alkyl, substituted with a poly(ethylene glycol) and a poly(dimethyl siloxane).

In another embodiment, R' is hydrogen and R is -R ^a -OC(O)NHCH ₂ -R ^b , R ^a is a C1-C2 alkylene and R ^b is -C(O)O-(C4-C16 alkyl).

In another embodiment, R' is hydrogen and R is -R ^a -OC(O)NH-R ^c , R ^a is a C1-C2 alkylene and R ^c is -(C4-C16 alkyl).

In another embodiment, R' is hydrogen and R is R ^a -C(O)NH-R ^d , R ^a is a Cl- C2 alkylene and R ^d is a C1-C2 alkyl, substituted with a poly(ethylene glycol) and a poly(dimethyl siloxane).

In another embodiment, R' is hydrogen and R is -R ^a -C(O)O-R ^d , R ^a is a Cl- C2 alkylene and R ^d is a C1-C2 alkyl, substituted with a poly(ethylene glycol) and a poly(dimethyl siloxane).

In alternative embodiments, the polymer employed in the sensing element can be a random or block copolymer comprising two or more different subunits of formula (I). In some embodiments, copolymer comprises at least one unit represented by formula (IA):

where m and n are each independently zero or an integer from 1 to 50, preferably, from 1 to 20. The values and preferred values of the variables in formula (IA) are as defined above with respect to formula (I).

Preferably, the unit of formula (IA) is represented by structural formulas (VIII) and (IX):

where q is 1 or 2, and p is an integer from 1 to 50,

r is 1 or 2, and s is an integer from 1 to 50. The values and preferred values of the variables in formulas (VIII) through (IX) are as defined above with respect to formulas (I) and (IA).

In another embodiment, the polymer employed in the sensing element can be a copolymer of fluorene and thiophene. In one embodiment, the fluorene-thiophene copolymer is a polymer having at least one unit represented by structural formula (IB): wherein each R" is independently an R as defined above with respect to formula (I). Preferably, each R" is independently a C1-C20 alkyl or a C6-C18 aryl. More preferably, each R" is independently a C6-C16 alkyl or a C6-C14 aryl. Even more preferably, each R" is independently a C4-C16 alkyl. The values and preferred values of the remainder of the variables in formula (IB) are as defined above with respect to formula (I).

In preferred embodiments, the polymer that comprises at least one unit of formula (IB), comprises at least one unit represented by the structural formulas (X) through (XIII):

(XIII).

The values and preferred values of the variables in formulas (X) through (XIII) are as defined above with respect to formulas (I) and (IB).

Preferably, the polymer is a thiophene-based polymer comprising at least one unit represented by the following structural formulas:

Preferably, the polymer is PURET, a thiophene-based polymer that comprises at least one subunit selected from structural formula (II), above.

Synthetic schemes for the polymers described above are well-known in the art. For example, PURET can be synthesized by the method described in Chittibabu, K.G.; Balasubramanian, S.; Kim, W.H; Cholli, A.L.; Kumar J.; Tripathy, S.K. J. Macromol. Sci. Pure Appl. Chem. 1996, A33, 1283-1300, the entire teachings of which are incorporated herein by reference. Preferably, the synthesis and polymerization involve only two chemical steps that reduce the fabrication cost. The preferred method of PURET synthesis is described in Scheme I:

FeCI ₃ ZCHCI ₃ (Scheme I)

The use of thiophene-based polymers confers a number of important advantages. In one embodiment, the sensing element of this invention absorbs in the range of 350 nm to 500 nm and emits in the range of 550 nm to 700 nm. For example, FIG. 1 is a plot showing the absorption spectra of PURET in either a thin film or a solution. FIG. 2 is a plot showing the emission spectra of PURET in either a thin film or a solution. Light emitting diodes (LEDs) and detectors operable in this range are readily available, making the device employing such sensing elements inexpensive. The thiophene-based polymers are very stable in ambient light, resulting in long service life.

Because the thiophene-containing polymers that contain at least one subunit represented by formula (I) are soluble in most of the organic solvents, they lend themselves to thin-film fabrication. Typically, thiophene-based polymers exhibit very large Stake's shift, which is very advantageous in discriminating the excitation wavelength with the emission wavelength. Furthermore, thiophene-based polymers that comprise at least one unit of formula (I) permit modification of the thiophene moiety with one or two side groups. In certain embodiments, a side group attached to the polymer backbone prevents aggregation and enhances quantum yield. Using the side groups, the properties of the polymer can be tailored to prevent π-stacking and to enhance interaction with the analyte which quenches the fluorescence. Moreover, a desirable side group can be employed for better interactions with analytes. For example, a hydrogen bond- forming group can be placed on the thiophene moiety to promote interaction with an analyte (the compound to be detected). In another embodiment, the sensing element comprises a copolymer. The copolymer can be a random copolymer or a block copolymer. Copolymer can include one or more different chromophores. A combination of different choromophores can provide energy migration pathways to excitons, thereby leading to enhanced sensitivity.

Devices and Methods of the Present Invention

In a preferred embodiment, a sensing element comprises one or more of the fluorescent (co)polymers described above. In one embodiment, the present invention is a device. The device comprises a film of the (co)polymer disposed on the substrate. The (co)polymer comprises at least one subunit of formula (I). One of ordinary skill in the art will be able to select a suitable substrate. In one embodiment, the substrate is glass. In another embodiment, the substrate is a

(meth)acrylate polymer, a polyurethane or a polycarbonate. One of ordinary skill in the art will understand that there are a wide variety of methods for making optical quality thin films for the devices. Examples include spin-coating, drop-casting or adsorption from solution.

In certain embodiments, the device further includes a light source of suitable wavelength, such as light-emitting diode, and a detector sensitive in a suitable waveband, such as photodiodes, photomultiplier tubes or a charge-coupled device

(CCD). In other embodiments, the device further comprises a general purpose or a special purpose computer for processing the collected data.

One embodiment of the device of the present invention is schematically depicted in FIG. 3. Device (100) comprises light source (102), detector (104), sample holder (106), and processor (108). Optionally, device (100) can also include optical elements (110) and (112) {e.g., lenses, mirrors, prisms, light guides), as well as spatial filter (114) and spectral bandwidth filter (116). An amplifier (118) receives reference signal (120) from the light source (102) and the signal (122) from detector (104) and transmits these signals to processor (108). In another embodiment, the present invention is a method of detecting chemical compounds in a sample, whereby a sample is exposed to a (co)polymer that comprises at least one subunit of formula (I). Fluorescent emission by the (co)polymer is detected. Diminishing fluorescence of the polymer is indicative of the presence of at least one chemical compound in the sample. Preferably, the compound is a nitrogen-containing compound. More preferably, the compound contains at least one nitroamine moiety. Even more preferably, the compound is one or more of RDX, HMX and PETN. Compounds of the Present Invention

In some embodiments, the present invention is a polymer comprising at least one unit represented by the structural formulas (VIII) and (IX):

where q is 1 or 2, and p is an integer from 1 to 50,

(IX), r is 1 or 2, and s is an integer from 1 to 50. The values and preferred values of the variables in formulas (VIII) through (IX) are as defined above with respect to formulas (I) and (IA).

In some embodiments, the present invention is a polymer comprising at least one unit represented by the structural formulas (X) through (XIII):

(XIII).

The values and preferred values of the variables in formulas (X) through (XIII) are as defined above with respect to formulas (I) and (IB).

EXEMPLIFICATION

Example 1 : Detection of RDX by PURET Effect of RDX

NO ₂

O,N NO,

RDX on fluorescence of PURET (the polymer of formula (II)) was measured in solution as well as in thin films of PURET.

A thin film of poly[2-(3-thienyl)ethanol n-butoxy carbonylmethylurethane] (PURET), was prepared as follows. Thin films were prepared using spin coating. Dilute solutions of the polymer in tetrahydofuran or chloroform were prepared and the film was coated on glass substrate at 1000 RPM yielding films having a thickness of about 30 nm.

A solution of PURET in THF was prepared as follows. A required amount of polymer was measured using a chemical balance and mixed in THF in a glass vial.

Fluorescence of the PURET in a THF solution was measured at various RDX concentrations, according to the following protocol. RDX was dissolved in THF. The fluorescence of a freshly prepared PURET solution was recorded, a known quantity of RDX solution was then added, and change in fluorescence caused by the RDX solution was measured. The amount of RDX was increased sequentially. The dilution effect due to the presence of solvent was also tested at each and every stage.

Fluorescence of the thin film of PURET was measured in the presence of vapor phase RDX, according to the following protocol. The analyte (60 mg of RDX) was placed inside a quartz cuvette (1 cm x 1 cm and 4 ml volume) and closed to allow the vapor to become saturated. The fluorescence measurements were carried out by inserting the spin-coated thin film disposed on a glass substrate in a closed cuvette containing saturated vapors of the analytes at room temperature (25 ⁰ C). Proper care was taken to avoid the direct contact of the polymer thin film with solid analytes. RDX vapor pressure is 5 ppt. The change in fluorescence occured due to the interaction of polymer and vapor of analytes. Fluorescence measurements were performed at an excitation wavelength of 460 nm using commercially available fluorimeter (PerkinElmer LS 55 Luminescence Spectrometer).

The data is presented in FIG. 4A (in solution) and FIG. 4B (thin film). The data demonstrated that thin films of PURET possessed a superior sensitivity to RDX vapor, when compared to the sensitivity to dissolved RDX of PURET in THF solution.

Example 2: Detection of Explosives using PURET Thin Film Effect of TNT, DNT, RDX, HMX and PETN:

RDX HMX on fluorescence of a thin film of poly[2-(3-thienyl)ethanol n-butoxy carbonylmethylurethane (compound of formula (II), PURET),

was measured.

The thin film of PURET was prepared as follows. Thin film of PURET was prepared using spin-coating. Dilute solutions of the polymer in tetrahydofuran or chloroform were prepared, and the film was coated on a glass substrate at 1000 RPM yielding films of thickness about 30 nm. Fluorescence of the thin film of PURET was measured in the presence of vapor phases of TNT, DNT, RDX, HMX and PETN according to the following protocol.

The analytes (60 mg of each TNT, DNT, RDX, HMX or PETN) were each placed inside a separate quartz cuvette (1 cm x 1 cm and 4 ml volume) and closed to allow the vapor to become saturated. The fluorescence measurements were carried out by inserting the spin-coated thin film disposed on a glass substrate in a closed cuvette containing saturated vapors of the analytes at room temperature (25 C). Proper care was taken to avoid direct contact of the polymer thin film with solid analytes. A change in fluorescence occured due to the interaction of polymer and vapor of analytes. The fluorescence measurements were performed at an excitation wavelength of 460 nm using commercially available fluorimeter (PerkinElmer LS 55 Luminescence Spectrometer).

Table 1 shows the vapor pressures at room temperature, as well as dipole moments, of selected nitrogen-containing compounds detected using the devices and methods of the present invention. Table 1

The data is presented in FIG. 5. The data demonstrates that RDX was detected at few parts per trillion (ppt) level in vapor phase. TNT, DNT, RDX, HMX and PETN were all detected at very low concentrations in vapor phase. The data presented in FIG. 5 demonstrated that low vapor pressure explosives such as PETN, HMX and RDX could be detected by the thin films of PURET.

Example 3 : Polymer Nanofiber Functionalized Fluorescence-based Sensors for Explosives The effect of RDX vapor on the fluorescence of solid thin film of poly [3-(2- ethyl-isocyanato-octa-decanyl)-thiophene (ADS518PT) was investigated. The structure of the polymer is represented by structural formula (VII):

Thin film of the polymer was prepared using spin coating. Dilute solution of the polymer in tetrahydofuran or chloroform were prepared, and the film was coated on a glass substrate at 1000 RPM yielding films of thickness about 30 nm.

The fluorescence was measured according to the following protocol. Each analyte (60 mg of RDX, DNT or TNT) was placed inside a quartz cuvette (1 cm x 1 cm and 4 ml volume) and closed to allow the vapor to become saturated. The fluorescence measurements were carried out by inserting the spin-coated thin film disposed on a glass substrate in a closed cuvette containing saturated vapors of the analytes at room temperature (25 ⁰ C). Proper care was taken to avoid the direct contact of the polymer thin film with solid analytes. The change in fluorescence occured due to the interaction of polymer and vapor of analytes. The fluorescence measurements were performed at an excitation wavelength of 460 nm using commercially available fluorimeter (PerkinElmer LS 55 Luminescence Spectrometer).

FIG. 6 shows the fluorescence quenching of solid film in the presence of DNT, TNT and RDX vapor. The polymer showed good sensitivity for RDX in vapor phase and was compared with PURET, a polymer having subunits represented by structural formula (IV):

FIG. 7 is a plot showing the fluorescence quenching of solid thin film of ADS518PT (formula (VII)) and of PURET (formula (H)) in the presence of RDX vapor. With PURET thin film, the observed fluorescence quenching in the presence of RDX vapor was 20% in 60 seconds, which increases to 30% in 2 minutes. With ADS518PT thin film, the observed fluorescence quenching in the presence of RDX vapor was 5% in 60 seconds, increasing to 20% in 5 minutes. ADS518PT was a second polythiophene which responded to RDX at a vapor pressure of 5 parts per trillion in addition to PURET.

Example 4 : Detection of HMX and PETN by PURET Thin Film

The effect of vapors of HMX and PETN on fluorescence of a thin film of poly[2-(3-thienyl)ethanol n-butoxy carbonylmethylurethane (compound of formula (II), PURET),

was measured.

The thin film of PURET was prepared as follows. Thin film of the polymers was prepared using spin coating. Dilute solution of polymer in tetrahydofuran or chloroform were prepared, and the film was coated on a glass substrate at 1000 RPM yielding films of thickness about 30 nm. Fluorescence of the PURET in a thin film was measured in the presence of vapor phases of HMX and RDX according to the following protocol. The analytes (60 mg of each RDX or HMX) were placed inside a quartz cuvette (1 cm x 1 cm and 4 ml volume) and closed to allow the vapor to become saturated. The fluorescence measurements were carried out by inserting the spin-coated thin film disposed on a glass substrate in a closed cuvette containing saturated vapors of the analytes at room temperature (25 ⁰ C). Proper care was taken to avoid the direct contact of the polymer thin film with solid analytes. HMX the vapor pressure was significantly lower than RDX (5 ppt). The change in fluorescence occurred due to the interaction of polymer and vapor of analytes. The fluorescence measurements were performed at an excitation wavelength of 460 nm using a commercially-available fluorimeter (PerkinElmer LS 55 Luminescence Spectrometer).

The results are presented in FIG. 8, which showed decreases in relative intensity of fluorescence of a PURET thin film as a function of time in the presence of with RDX or HMX. EQUIVALENTS

While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.