FIELD OF THE INVENTION The present invention relates to the use of phthalocyanine compounds and arene- anellated phthalocyanine compounds with aryl or hetaryl substituents in gas sensors, in particular for sensing oxidizing gases.

DESCRIPTION OF THE RELATED ART

Gas sensors have found wide application in various technical fields, e.g. in the field of work safety and environmental protection for detecting toxic or irritant gases or vapors like CO and NO2, as well as in air conditioning in cars, airplanes, houses etc. to ethanol sensors for breath analyzers. Oxidizing gases, like ozone O3, are analytes of growing interest due to increased concern about pollution and the resulting health hazards. The concentration of ozone in the ambient air due to increased traffic, but also in offices due to laser printers and photocopiers is of particular interest because ozone is the main factor leading to photochemical smog. Different types of chemical sensors are known, in particular electronic conductance sensors, mass-sensitive-sensors utilizing a quartz crystal microbalance, surface acoustic-wave sensors and optical sensors. In electronic conductance sensors the sensor response is defined as the relative variation in conductance due to the introduction of a gas. Conductometric semiconductor thin films are the most promising devices among solid state chemical sensors due to their small dimensions, low cost, low power consumption, on-line operation, and high compatibility with microelectronic processing.

A material that changes its electrical resistivity (or conductivity) depending on a change in the surrounding chemical environment is denoted as a chemiresistor. Several different materials are known to have chemiresistor properties. Thus, several semiconductor materials, like metal oxide semiconductors, exhibit electrical

conductivities that are strongly affected by ambient gases and vapours. In principle, metalated and metal-free phthalocyanines (Pc) are organic

semiconductors that are promising candidates for gas sensors. They are chemically sensitive to reactive gases and can be oxidized or reduced. Typically, phthalocyanines are insulating in a dark high vacuum environment, but exposure to minute amounts of atmospheric impurities or dopants can give them semiconductor properties that can be associated with a remarkable change in conductivity. Metal-free phthalocyanines (hbPc) and phthalocyanines with different metal centres (Mg, Fe, Mn, Co, Ni, Cu, Zn, Pb, Al, Pt, etc.) are well known for sensing gases, like NO2 and O3. It is described to employ unsubstituted Pc as well as Pc with substitution at peripheral and non- peripheral positions. Substitution known for Pc that are employed as gas sensors are generally alkyl, alkoxy, carboxy, thiols, crown ether groups, phenoxy groups, amines, amides, sulfonamides, alkylamines, halogens, like fluorine, chlorine, bromine, etc. From the literature, it seems that materials with electron donating groups are more sensitive to the sensing of oxidizing gases.

R. Zhou et al. give in Applied Organometallic Chemistry (1996), 10, 557-577 an overview over phthalocyanines as sensitive materials for chemical sensors.

T. A. Jones and B. Bott describe in Sensors and Actuators B (1986), 9, 27-37 gas- induced electrical conductivity changes in metal phthalocyanines. The effect of NO2, NO, F2, BCI3, BF3, NH3, H2S, SO2 and HCI at low concentrations of less than 1 ppm in air on the electrical conductivity of a number of unsubstituted phthalocyanines (PbPc, ZnPc, CuPc, NiPc, CoPc, FePc and MgPc) was investigated. L. Torsi et al. describe in Sensors and Actuators B (2000), 67, 312-316 that organic thin-film-transistors (OTFT) can be used as gas sensors. Gas detection could be achieved by direct interaction of the analyte molecules with the transistor organic layer of the OTFT. Among a great number of different organic semiconductors also copper hexadecafluorophthalocyanine (Fi6CuPc) is mentioned.

Forest I. Bohrer et al. report in J. AM. CHEM. SOC. 2007, 129, 5640-5646 about the gas sensing mechanism in chemiresistive cobalt and metal-free phthalocyanine thin films. The gas sensing behaviors of cobalt phthalocyanine (CoPc) and metal-free phthalocyanine (H2-Pc) thin films were investigated with respect to the Lewis basicity of the analyte. Analytes were chosen to span a range of electron donor and hydrogen- bonding strengths, including dichloromethane, nitromethane, acetonitrile, 2-butanone, di- butyl ether, trimethyl phosphate, water, isophorone, dimethyl methylphosphonate (DMMP, a neurotoxin simulant), dimethyl sulfoxide (DMSO), A ,AAdimethylformamide (DMF), and triethylamine.

Forest I. Bohrer et al. describe in J. AM. CHEM. SOC. 2009, 131 , 478^185 the sensitivities of metallophthalocyanine chemiresistors (Co, Ni, Cu, Zn and H2) to vapor phase electron donors using 50 nm MPc films deposited on interdigitated electrodes. Sensor responses were measured as changes in current at constant voltage. The analytes were chosen to span a broad range of Lewis base and hydrogen bond base strengths.

John H. Shu et al. describe in Sensors and Actuators B 148 (2010) 498-503 a passive (unpowered) chemiresistor sensor based on an iron (II) phthalocyanine thin film for monitoring nitrogen dioxide.

Xiujin Wang et al. report in Sensors and Actuators B 160 (201 1 ) 1 15-120 about the fabrication of a room temperature nitrogen dioxide chemresistor using an ultrathin vanadyl-phthalocyanine film as active layer.

Kuo-Chuan Ho and Yi-Ham Tsou describe in Sensors and Actuators B 77 (2001 ) 253- 259 a chemiresistor-type NO gas sensor based on nickel phthalcyanine thin films.

Seung-Ryeol Kim et al. describe in Sensors and Actuators B (1997), 40, 39-45 the N02-sensing properties of octa(2-ethylhexyl) metallophthalocyanine films prepared by using the Langmuir-Blodgett (LB) method. The absorption capacities to NO2 of hbPc, CuPc, CoPc and PbPc were investigated.

M. Nicolau et al. describe in Synthetic Metals 102 (1999), 1462-1463 the gas sensing ability of spin-coated films of substituted sulfur containing Pc.

Ximing Ding and Huijun Xu describe in Sensors and Actuators B (2000), 65, 108-1 10 the gas-sensing properties of asymmetrically substituted amphiphilic Pc:

B. Wang et. al compare in Sensors and Actuators B (201 1 ), 152, 191 -195 the gas sensing properties in spin-coating films of tetra-(tert-butyl)-5,10,15,20-tetraaza- porphyrin copper (CuTAP(t-Bu)4) and tetra-(tert-butyl) phthalocyanine copper (CuPc(t-Bu)4). Necmettin Kilinc et al. describe in Sensors and Actuators B (2012), 173, 203-210 the electrical and nitrogen dioxide (NO2) sensing properties of a series liquid-crystalline octakisalkylthiophthalocyanine (C6S) ₈ PcM [M = 2H, Ni, Cu, Zn] thin film. P.S. Barker et al. describe in Thin Solid Films (1996), 284-285, 94-97 a hybrid

Pc/silicon field-effect transistor based on a metal-free octahexyl-substituted Pc for sensing NO2.

Teruhisa Kudo et al. describe in Journal of Porphyrins and Phthalocyanines (1999), 3, 65-69) the fabrication of gas sensors based on soluble phthalocyanines of the general formula (A)

(A)

wherein M is Cu, Co or Ni.

Most existing gas sensors are still based on metal oxides. However, those sensors need improvement in at least one of the following aspects: high power consumption, bulky size, high production costs, low selectivity and long response time.

Also the phthalocyanines employed in gas sensors are still unsatisfactory in terms of long term material stability, high selectivity towards certain analytes, short response time and good recovery after termination of the contact with an analyte. Thus, there is a need to provide phthalocyanines for gas sensors that show an improvement of at least one of the afore-mentioned properties. It has now been found that, surprisingly, phthalocyanine compounds with annelated aromatic rings and/or with certain substituents that are bound to the fused arene ring of the pyrrol moiety by a single bond or are linked via sulphur or nitrogen to the fused arene ring of the pyrrol moiety, are particularly suitable for the use in the active layer of gas sensing chips.

SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a sensor for gases, in particular for oxidizing gases, wherein the active area of the sensor comprises at least one compound of the formula la or lb

(la) (lb) or a mixture thereof, where

M is a divalent metal, a divalent metal atom containing group or a divalent metalloid group;

A at each occurrence, is independently of each other a fused arene ring selected from the group consisting of a benzene ring, naphthalene ring, anthracene ring and phenanthrene ring;

R ^a at each occurrence, is independently selected from aryl, arylthio,

monoarylamino, diarylamino, hetaryl, hetaryloxy, oligo(het)aryl and

oligo(het)aryloxy, wherein each aryl, arylthio, monoarylamino, diarylamino, hetaryl, hetaryloxy, oligo(het)aryl and oligo(het)aryloxy is unsubstituted or carries at least one substituent R ^aa independently selected from cyano, hydroxyl, nitro, carboxyl, halogen, alkyl, haloalkyl, cycloalkyl, halocycloalkyl, alkoxy, haloalkoxy, alkylsulfanyl, haloalkylsulfanyl, amino, monoalkylamino, dialkylamino, NH(aryl) m is O, 1 , 2, 3, 4,5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22 or 23.

According to a further aspect of the present invention there is provided a sensor system comprising: a sensor chip having a plurality of sensors as defined above and in the following, a socket that mounts the sensor chip to a substrate and provides thermal and electrical interference isolation for the sensor chip; and

sensing circuitry mounted on the substrate for controlling sensing operations conducted by the plurality of sensors.

According to a further aspect of the present invention, there is provided a method for sensing oxidizing gases, comprising a) providing a sensor as defined above and in the following, b) exposing an analyte vapor to the sensor and measuring at least one electrical property of the active area of the sensor, and c) determining the concentration of oxidizing gas in said analyte vapor.

DETAILED DESCRIPTION OF INVENTION

The phthalocyanines of the formula la and lb employed as sensors materials show a remarkably high sensitivity to oxidizing gas, such as NO2 and O3. In many cases a lower limit of detection (treshhold value) of 10 ppb with regard to NO2 and of 20 ppb with regard to O3 is obtained.

The term "active region" as used herein is a region of a gas sensitive device whose respective output signals when it is in contact with the gas to be detected and when it is not in contact are different.

Electrical resistivity (also denoted as resistivity or specific electrical resistance) is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. Resistivity is commonly represented by the Greek letter p (rho). The SI unit of electrical resistivity is the ohm-metre (Ω-m). Electrical conductivity or specific conductance is the reciprocal of electrical resistivity and measures a material's ability to conduct an electric current. It is commonly represented by the Greek letter σ (sigma), but K (kappa) (especially in electrical engineering) or γ (gamma) are also occasionally used. Its SI unit is Siemens per metre (S/m).

The expression "halogen" denotes in each case fluorine, bromine, chlorine or iodine, particularly chlorine or fluorine.

In the context of the present invention, the expression "alkyl" comprises straight-chain or branched alkyl groups. Alkyl is preferably Ci-C3o-alkyl, more preferably Ci-C2o-alkyl and most preferably Ci-Ci2-alkyl. Examples of alkyl groups are especially methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neo-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl and n-eicosyl.

The expression alkyl also comprises alkyl radicals whose carbon chains may be interrupted by one or more nonadjacent groups which are selected

from -0-, -S-, -NR ^e -, -C(=0)-, -S(=0)- and/or -S(=0) ₂ -. R ^e is preferably hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl or hetaryl.

The above remarks regarding alkyl also apply to the alkyl moiety in alkoxy and alkylsulfanyl (= alkylthio).

In the context of the present invention, the term "haloalkyi" comprises straight-chained or branched alkyl groups, wherein some or all of the hydrogen atoms in these groups are replaced by halogen atoms. Suitable and preferred alkyl groups are the afore- mentioned. The halogen atoms are preferably selected from fluorine, chlorine and bromine, more preferably from fluorine and chlorine. Examples of haloalkyi groups are especially chloromethyl, bromomethyl, dichloromethyl, trichloromethyl, fluoromethyl, difluoromethyl, trifluoromethyl, chlorofluoromethyl, dichlorofluoromethyl,

chlorodifluoromethyl, 1 -chloroethyl, 1 -bromoethyl, 1 -fluoroethyl, 2-fluoroethyl,

2,2-difluoroethyl, 2,2,2-trifluoroethyl, 2-chloro-2-fluoroethyl, 2-chloro-2,2-difluoroethyl,

2.2- dichloro-2-fluoroethyl, 2,2,2-trichloroethyl and pentafluoroethyl, 2-fluoropropyl, 3-fluoropropyl, 2,2-difluoropropyl, 2,3-difluoropropyl, 2-chloropropyl, 3-chloropropyl,

2.3- dichloropropyl, 2-bromopropyl, 3-bromopropyl, 3,3,3-trifluoropropyl,

3,3,3-trichloropropyl, CH ₂ -C ₂ F ₅ , CF ₂ -C ₂ F ₅ , CF(CF ₃ ) ₂ , 1 -(fluoromethyl)-2-fluoroethyl, 1 -(chloromethyl)-2-chloroethyl, 1 -(bromomethyl)-2-bromoethyl, 4-fluorobutyl,

4- chlorobutyl, 4-bromobutyl, nonafluorobutyl, 5-fluoro-1 -pentyl, 5-chloro-1 -pentyl,

5- bromo-1 -pentyl, 5-iodo-1 -pentyl, 5,5,5-trichloro-1 -pentyl, undecafluoropentyl,

6- fluoro-1 -hexyl, 6-chloro-1 -hexyl, 6-bromo-1 -hexyl, 6-iodo-1 -hexyl, 6,6,6-trichloro- 1 -hexyl or dodecafluorohexyl.

The above remarks regarding haloalkyi also apply to the haloalkyi moiety in haloalkoxy and haloalkylsulfanyl (also referred to as haloalkylthio). In the context of the present invention, the term "cycloalkyl" denotes a cycloaliphatic radical having usually from 3 to 10, preferably 5 to 8, carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, norbornyl, bicyclo[2.2.2]octyl or adamantyl. In the context of the present invention, the term "halocycloalkyl" comprises cycloalkyl groups as mentioned above, wherein some or all of the hydrogen atoms in these groups may be replaced by halogen atoms as mentioned above.

In the context of the present invention, the term "aryl" refers to mono- or polycyclic aromatic hydrocarbon radicals. Aryl usually is an aromatic radical having 6 to 24 carbon atoms, preferably 6 to 20 carbon atoms, especially 6 to 14 carbon atoms as ring members. Aryl is preferably phenyl, naphthyl, indenyl, fluorenyl, anthracenyl, phenanthrenyl, naphthacenyl, chrysenyl, pyrenyl, coronenyl, perylenyl, etc., and more preferably phenyl or naphthyl.

Substituted aryls may, depending on the number and size of their ring systems, have one or more (e.g. 1 , 2, 3, 4, 5 or more than 5) substituents independently selected from the substituents R ^aa as defined above. Aryl which bears one or more substituents R ^aa is, for example, 2-, 3- and

4-methylphenyl, 2,4-, 2,5-, 3,5- and 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2-, 3- and 4-ethyl-phenyl, 2,4-, 2,5-, 3,5- and 2,6-diethylphenyl, 2,4,6-triethylphenyl, 2-, 3- and 4-propyl-phenyl, 2,4-, 2,5-, 3,5- and 2,6-dipropylphenyl, 2,4,6-tripropylphenyl, 2-, 3- and 4-isopropylphenyl, 2,4-, 2,5-, 3,5- and 2,6-diisopropylphenyl,

2,4,6-triisopropylphenyl, 2-, 3- and 4-butylphenyl, 2,4-, 2,5-, 3,5- and 2,6-dibutylphenyl, 2,4,6-tributylphenyl, 2-, 3- and 4-isobutylphenyl, 2,4-, 2,5-, 3,5- and

2,6-diisobutylphenyl, 2,4,6-triisobutylphenyl, 2-, 3- and 4-sec-butylphenyl, 2,4-, 2,5-, 3,5- and 2,6-di-sec-butylphenyl, 2,4,6-tri-sec-butylphenyl, 2-, 3- and 4-tert-butylphenyl, 2,4-, 2,5-, 3,5- and 2,6-di-tert-butylphenyl and 2,4,6-tri-tert-butylphenyl; 2-, 3- and 4-methoxyphenyl, 2,4-, 2,5-, 3,5- and 2,6-dimethoxyphenyl, 2,4,6-trimethoxyphenyl, 2-,

3- and 4-ethoxyphenyl, 2,4-, 2,5-, 3,5- and 2,6-diethoxyphenyl, 2,4,6-triethoxyphenyl, 2-, 3- and 4-propoxyphenyl, 2,4-, 2,5-, 3,5- and 2,6-dipropoxyphenyl, 2-, 3- and

4- isopropoxyphenyl, 2,4-, 2,5-, 3,5- and 2,6-diisopropoxyphenyl and 2-, 3- and

4-butoxyphenyl; 2-, 3- and 4-cyanophenyl, and the like.

The above remarks regarding aryl also apply to the aryl moiety in aryloxy and arylsulfanyl (also referred to as arylthio). Representative examples of aryloxy include phenoxy and naphthyloxy. Substituted aryloxy may, depending on the number and size of their ring systems, have one or more (e.g. 1 , 2, 3, 4, 5 or more than 5) substituents independently selected from the substituents R ^aa as defined above. Representative examples of arylthio include phenylthio (also referred to as phenylsulfanyl) and naphthylthio. Substituted arylthio may, depending on the number and size of their ring systems, have one or more (e.g. 1 , 2, 3, 4, 5 or more than 5) substituents independently selected from the substituents R ^aa as defined above.

In the context of the present invention, the term "hetaryl" (also referred to as heteroaryl) refers to heteroaromatic mono- or polycyclic radicals, comprising, in addition to ring carbon atoms, 1 , 2, 3, 4 or more than 4 heteroatoms as ring members. The

heteroatoms are preferably selected from oxygen, nitrogen, selene and sulphur.

Preferably, hetaryl denotes a radical having 5 to 18, for example 5, 6, 8, 9, 10, 1 1 , 12, 13 or 14 ring members. The hetaryl radical may be attached to the remainder of the molecule via a carbon ring member or via a nitrogen ring member.

If hetaryl is a monocyclic radical, examples are 5- or 6-membered hetaryl, such as

2- furyl (furan-2-yl), 3-furyl (furan-3-yl), 2-thienyl (thiophen-2-yl), 3-thienyl (thiophen-

3- yl), selenophen-2-yl, selenophen-3-yl, 1 H-pyrrol-2-yl, 1 H-pyrrol-3-yl, pyrrol-1 -yl, imidazol-2-yl, imidazol-1 -yl, imidazol-4-yl, pyrazol-1 -yl, pyrazol-3-yl, pyrazol-4-yl, pyrazol-5-yl, 3-isoxazolyl, 4-isoxazolyl, 5-isoxazolyl, 3-isothiazolyl, 4-isothiazolyl,

5- isothiazolyl, 2-oxazolyl, 4-oxazolyl, 5-oxazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 1 ,2,4-oxadiazol-3-yl, 1 ,2,4-oxadiazol-5-yl, 1 ,3,4-oxadiazol-2-yl, 1 ,2,4-thiadiazol-3-yl, 1 ,2,4-thiadiazol-5-yl, 1 ,3,4-thiadiazol-2-yl, 4H-[1 ,2,4]-triazol-3-yl, 1 ,3,4-triazol-2-yl, 1 ,2,3-triazol-1 -yl, 1 ,2,4-triazol-1 -yl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl, 3-pyridazinyl,

4- pyridazinyl, 2-pyrimidinyl, 4-pyrimidinyl, 5-pyrimidinyl, 2-pyrazinyl, 1 ,3,5-triazin-2-yl and 1 ,2,4-triazin-3-yl. Preferred monocyclic hetaryl radicals include 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 1 H-pyrrol-2-yl, 1 H-pyrrol-3-yl, thiazol-2-yl, thiazol-5-yl,

[1 ,3,4]thiadiazol-2-yl and 4H-[1 ,2,4]-triazol-3-yl. If hetaryl is a polycyclic radical, hetaryl has multiple rings (e.g. bicyclic, tricyclic, tetracyclic hetaryl) which are fused together. The fused-on ring may be aromatic, saturated or partially unsaturated. Examples of polycyclic hetaryl are quinolinyl, isoquinolinyl, indolyl, isoindolyl, indolizinyl, benzofuranyl, isobenzofuranyl,

benzothiophenyl, benzoxazolyl, benzisoxazolyl, benzthiazolyl, benzoxadiazolyl;

benzothiadiazolyl, benzoxazinyl, benzopyrazolyl, benzimidazolyl, benzotriazolyl, benzotriazinyl, benzoselenophenyl, thienothiophenyl, thienopyrimidyl, thiazolothiazolyl, dibenzopyrrolyl (carbazolyl), dibenzofuranyl, dibenzothiophenyl,

naphtho[2,3-b]thiophenyl, naphtha[2,3-b]furyl, dihydroindolyl, dihydroindolizinyl, dihydroisoindolyl, dihydrochinolinyl, dihydroisochinolinyl.

In the case of substituted hetaryl radicals, the substitution is usually on at least one carbon and/or nitrogen ring atom(s). Suitable substituents of the hetaryl radicals are independently selected from the substituents R ^aa as defined above. It is a matter of course that the maximum possible number of substituents depends on the size and number of heteroaromatic rings. The number of possible substituents ranges usually from 1 to more than 5, for example 1 , 2, 3, 4, 5 or 6. In the context of the present invention the expression "5-membered sulphur containing hetaryl which may contain additionally 1 or 2 nitrogen atoms as ring members and may carry a fused-on arene ring" denotes hetaryl having carbon atoms and one sulphur atom and optionally one or two nitrogen atoms within the 5-membered ring, wherein the 5-membered ring is optionally fused with one or two arene rings. Preferably, the 5-membered ring does not carry a fused-on arene ring or is fused with one arene ring. The fused-on arene rings are preferably selected from benzene, naphthalene, phenanthrene or anthracene. Examples are 2-thienyl, 3-thienyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 3-isothiazolyl, 4-isothiazolyl, 5-isothiazolyl, 1 ,2,4-thiadiazol-3-yl,

1 ,2,4-thiadiazol-5-yl, 1 ,3,4-thiadiazol-2-yl, benzo[b]thienyl, benzthiazolyl,

benzothiadiazolyl, naphtho[2,3-b]thiophenyl or dibenzo[b,d]thiophenyl.

In the context of the present invention, the expression "oligo(het)aryl" group refers to unsubstituted or substituted oligomers having at least one repeat unit. The repeat unit is selected from an arenediyl group and a hetarenediyl group. Accordingly, in one embodiment the repeat unit consists of at least one arenediyl group, in another embodiment the repeat unit consists of at least one hetarenediyl group and in a further embodiment the repeat unit consists of at least one arenediyl group and at least one hetarenediyl group. The arenediyl group is a divalent group derived from an arene, preferably benzene or naphthalene, such as 1 ,2-phenylene (o-phenylene), 1 ,3-phenylene (m-phenylene), 1 ,4-phenylene (p-phenylene), 1 ,2-naphthylene, 2,3-naphthylene, 1 ,4-naphthylene and the like. The arenediyl group is a divalent group derived from a hetarene. Preferably, the hetarenediyl group is a divalent group derived from thiophene or furan.

The repeat unit is usually terminated with a monovalent group derived from the repeat unit. Each arenediyl group, each hetarenediyl group and the terminal group may be unsubstituted or substituted by 1 , 2, 3, 4 or more than 4 substituents R ^aaa . R ^aaa at each occurrence is selected from alkyl, halogen, haloalkyi, alkoxy and haloalkoxy, preferably alkyl. The repeat units are bonded to another via a single bond. In the case of the thiophendiyl group and the furandiyl group, these groups are preferably covalently linked at the 2 position. The number of repeat units usually is in the range from 2, 3, 4, 5, 6, 7, 8 or more than 8, preferably 2, 3 or 4. In the following, oligo(het)aryl groups comprising at least one hetarenediyl group are also referred to as oligohetaryl groups.

wherein R ^aaa is as defined above, preferably alkyl, especially Ci-Cio-alkyl, x is 0, 1 or 2 and y is 0, 1 , 2, 3 or 4.

Examples of oligo(het)aryl groups are

wherein # is the point of attachment to the remainder of the molecule, a is 1 , 2, 3, 4, 5, 6, 7, or 8, y is 0, 1 , 2, 3 or 4, x is 0, 1 , 2 and x' is 0, 1 , 2 or 3 and R ^aaa is as defined above.

Preferred examples of oligo(het)aryl groups are biphenylyl, p-terphenylyl,

m-terphenylyl, o-terphenylyl, quaterphenylyl, e.g. p-quaterphenylyl, quinquephenylyl, e.g. p-quinquephenylyl and 2,2'-bifuran-5-yl.

Preferred examples of oligo(het)aryl groups are also unsubstituted oligothiophenyl groups of the formula

wherein # is the point of attachment to the remainder of the molecule and a is 1 , 2, 3, 4, 5, 6, 7, or 8. A preferred example is 2,2'-bithiophen-5-yl. Preferred examples of oligo(het)aryl groups are also substituted oligothiophenyl groups of the formula

wherein # is the point of attachment to the remainder of the molecule and a is 1 , 2, 3, 4, 5, 6, 7, or 8. A preferred example is 5'-hexyl-2,2'-bithiophen-5-yl.

In the context of the present invention, carboxylate is a derivative of a carboxylic acid function, in particular a metal carboxylate, a carboxylic ester function, such as -CO2R' with R' being an alkyl group or aryl group, or a carboxamide function. Sulfonate is a derivative of a sulfonic acid function, in particular a metal sulfonate, a sulfonic acid ester function or a sulfonamide function.

In general, compounds of the formulae la and lb, carrying substituents on more than one fused arene ring A, e. g. on 2, 3 or 4 fused arene rings A, may exist as a mixture of regioisomers or as a single compound. In some cases several kinds of regioisomers may be present. In the present invention, the compound of the formulae la or lb may be used as a single compound or as a mixture of regioisomers. In the case, where a mixture of regioisomers is used, any number of regioisomers, any substitution positions in the isomer and any ratio of isomers may be used. All regioisomeric forms of a compound of formulae la and lb are intended, unless the specific isomeric form is specially indicated. The remarks made in the following with respect to preferred aspects of the invention, e.g. to preferred meanings of the variables of compounds of the formulae la or lb, apply in each case on their own or to combinations thereof. According to one embodiment of the invention, preference is given to compounds of the formula la.

According to a further embodiment of the invention, preference is given to compounds of the formula lb. Preference is given to those compounds of formula lb, wherein M is a divalent metal. Divalent metals may, for example, be chosen from those of groups 2, 8, 10, 1 1 , 12 and 14 of the Periodic Table. Divalent metals are, for example, Zn(ll), Cu(ll), Pb (II), Fe(ll), Ni(ll), Cd(ll), Ag(ll), Mg(ll) or Sn(ll). Particular preference is given to compounds of the formula lb, wherein M is Zn(ll), Cu(ll), Ni(ll) or Pb(ll). A special embodiment are compounds of the formula lb, wherein M is Zn(ll).

Preference is also given to those compounds of the formula lb, wherein M is a divalent metal atom containing group. A divalent metal atom containing group may, for example, be chosen from a divalent oxometal, a divalent hydroxymetal, or a divalent halogenometal moiety. In the divalent oxometal moiety, for example, the metal may be chosen from those of groups 4, 5, 7 and 14 of the Periodic Table. Examples of divalent oxometal moieties are V(IV)0, Mn(IV)0, Zr(IV)0, Sn(IV)0 or Ti(IV)0. In a divalent hydroxymetal moiety, the metal may be chosen from those of groups 4, 6, 13, 14 and 15 of the Periodic Table. Examples of divalent hydroxymetal moieties are AI(lll)OH, Cr(lll)OH, Bi(lll)OH, or Zr(IV)(OH) ₂ . In a divalent halogenometal moiety, the metal may be chosen from those of group 13 of the Periodic Table. Examples of divalent halogenometal moieties are, for example, AI(III)CI, AI(III)F, ln(lll)F or ln(lll)CI.

Preference is also given to those compounds of the formula lb, wherein M is a divalent metalloid moiety. In divalent metalloid moieties, the metalloid may be chosen from a metalloid of group 14 of the Periodic Table, e.g. silicon. With a tetravalent metalloid, two of the valences may be satisfied by ligands, such as hydrogen, hydroxy, halogen, e.g. fluorine or chlorine, alkyl, alkoxy, aryl or aryloxy. Examples of divalent metalloid moieties are Sihb, S1F2, SiC , Si(OH)2, Si(alkyl)2, Si(aryl)2, Si(alkoxy)2 and Si(aryloxy)2. In the compounds of the formulae la and lb, the fused-on rings A may have the same definition or different definitions.

Preference is given to those compounds of the formulae la and lb, wherein all fused-on rings A have the same definition. In particular, in the formulae la and lb, all rings A have the same meaning and are all a fused benzene ring or all a fused naphthalene ring.

If in the formula la or lb at least one ring A is a fused naphthalene ring, group A is preferably a group of the formula

wherein # is the point of attachment to the remainder of the molecule.

In one preferred embodiment of the invention the active area of the sensor comprises at least one compound of the formulae la or lb or a mixture thereof, wherein all rings A are a fused benzene ring.

In the compounds of the formulae la or lb, wherein all rings A are each a fused benzene ring, the substituents (R ^a ) _m may be located at any aromatic carbon of the fused benzene ring (the numbered positions on the benzene ring substructure indicate the positions, where the substituent(s) (R ^a ) _m may be covalently bonded). These compounds are also referred to as la-Pc or Ib-Pc.

(la-Pc) (Ib-Pc)

There are four possible positions for substitution on each of the benzene ring substructure. There are two possible linkage sites on each benzene ring substructure for substitution at the ortho position, namely the 1 and 4 position on the first benzene ring substructure, the 8 and 1 1 position on the second benzene ring substructure, the 15 and 18 position on the third benzene ring substructure and the 22 and 25 position on the fourth benzene ring substructure. Likewise, there are two possible linkage sites on each benzene ring substructure for substitution at the meta position, namely the 2 and 3 position on the first benzene ring substructure, the 9 and 10 position on the second benzene ring substructure, the 16 and 17 position on the third benzene ring substructure and the 23 and 24 position on the fourth benzene ring substructure.

Thus, a compound of the formulae la-Pc or Ib-Pc, referred to as

1 ,8(1 1 ),15(18),22(25)-tetrasubstituted phthalocyanine compound, denotes a compound of the formulae la-Pc or Ib-Pc carrying 4 substituents R ^a , namely one substituent R ^a in the 1 position, a further substituent R ^a either in the 8 or 1 1 position, a further substituent R ^a either in the 15 or 18 position and a further substituent R ^a either in the 22 or 25 position. These compounds are also referred to as ortho-tetrasubstituted phthalcyanine compounds or as compounds of the formulae la-oPc or Ib-oPc.

(la-oPc) (Ib-oPc)

Likewise, a compound of the formulae la-Pc or Ib-Pc, referred to as

2,9(10), 16(17), 23(24)-tetrasubstituted phthalocyanine compound, denotes a compound of the formulae la-Pc or Ib-Pc carrying 4 substituents R ^a , namely one substituent R ^a in the 2 position, a further substituent R ^a either in the 9 or 10 position, a further substituent either in the 16 or 17 position and a further substituent R ^a either in the 23 or 24 position. These compounds are also referred to as meta-tetrasubstituted

phthalcyanine compounds or as compounds of the formulae la-mPc or Ib-mPc.

In a further preferred embodiment of the invention the active area of the sensor comprises at least one compound of the formulae la or lb or a mixture thereof, wherein all rings A are a fused naphthalene ring. Examples of compounds of the formulae la or lb, wherein all rings A are each a fused naphthalene ring, include the following:

(la-1 ,2-Nc) (lb-1 ,2-Nc)

The compounds (la-1 ,2-Nc) and (lb-1 ,2-Nc) have structural isomers with regard to the position of the four naphthalene rings that shall also be encompassed by the formulae (la-1 ,2-Nc) and (lb-1 ,2-Nc). Those compounds may have the point groups D2h, C _s , C2v and C ₄ h. C ₄ h is the preferred isomer as it has the highest symmetry and stability. The compounds (la-1 ,2-Nc) and (lb-1 ,2-Nc) may be employed in pure form or in form of a mixture of at least two isomers.

The substituent(s) (R ^a ) _m may be located at any aromatic carbon of the naphthalene substructure (the formulae of compounds la-2,3-Nc or lb-2,3-Nc and la-1 ,2-Nc or lb-1 ,2-Nc show the numbering of the naphthalene ring system present). In compounds la-2,3-Nc or lb-2,3-Nc, the substituent(s) (R ^a ) _m may be located, for example, at the peripheral positions (2, 3, 4, 5, 1 1 , 12, 13, 14, 20, 21 , 22, 23, 29, 30, 31 or 32) and/or at any of the inner positions (1 , 6, 10, 15, 19, 24, 28 or 33). Preference is given to those compounds of the formulae la-2,3-Nc and lb-2,3-Nc, where the substituent(s) (R ^a ) _m are located at inner positions (1 , 6, 10, 15, 19, 24, 28 or 33).

In the compounds of the formulae la-1 ,2-Nc or lb-1 ,2-Nc, the substituent(s) (R ^a ) _m may be located at any aromatic carbon of the naphthalene substructure, for example at any of the peripheral positions (3, 4, 5, 6, 12, 13, 14, 15, 21 , 22, 23, 24, 30, 31 , 32, 33) and/or at any of the inner positions (1 , 2, 10, 1 1 , 19, 20, 28, 29). Preference is given to those compounds of the formulae la-1 ,2-Nc and lb-1 ,2-Nc, where the substituent(s) (R ^a )m are located at inner positions (1 , 2, 10, 1 1 , 19, 20, 28, 29).

In a special embodiment of the invention, the active area of the sensor comprises at least one compound of the formulae la-1 ,2-Nc or lb-1 ,2-Nc.

In a further preferred embodiment of the invention, the active area of the sensor comprises at least one compound of the formulae la or lb or a mixture thereof, wherein all rings A are a fused anthracene ring.

Examples of compounds of the formulae la or lb, wherein all rings A are a fused anthracene ring include the following:

These compounds are also referred to as la-2,3-Ac and lb-2,3-Ac.The substituent(s) (R ^a )m and (R ^b ) _n , if present, may be located at any aromatic carbon of the anthracene substructure (the numbered positions on the anthracene ring substructure indicate the positions, where the substituent(s) (R ^a ) _m and (R ^b ) _n may be covalently bonded). The substituent(s) (R ^a ) _m and (R ^b ) _n may be located, for example, at the peripheral positions (4, 5, 6, 7, 15, 16, 17, 18, 26, 27, 28, 29, 37, 38, 39, and/or 40) and/or at any of the inner positions (1 , 2, 8, 9, 13, 14, 19, 20, 24, 25, 30, 31 , 35, 36, 41 and/or 42).

Preference is given to those compounds of the formulae la-2,3-Ac and lb-2,3-Ac, where the substituent(s) (R ^a ) _m and (R ^b ) _n , if present, are located at inner positions (1 , 2, 8, 9, 13, 14, 19, 20, 24, 25, 30, 31 , 35, 36, 41 and/or 42).

Examples of compounds of the formulae la or lb, wherein all rings A are a fused phenanthrene ring include the following:

(la-9,10-Phc) (lb-9,10-Phc) These compounds are also referred to as la-9,10-Phc and lb-9,10-Phc. The substituent(s) (R ^a ) _m and (R ^b ) _n , if present, may be located at any aromatic carbon of the phenanthrene substructure (the numbered positions on the phenanthrene ring substructure indicate the positions, where the substituent(s) (R ^a ) _m and (R ^b ) _n may be covalently bonded). The substituent(s) (R ^a ) _m and (R ^b ) _n may be located e.g. at the positions 1 , 2, 3, 4, 5, 6, 7, 8,12, 13, 14, 15, 16, 17, 18, 19, 23, 24, 25, 26, 28, 29, 30, 34, 36, 37, 38, 39, 40 and/or 41.

In a special embodiment, the sensor comprises at least one compound selected from compounds of the formulae la-oPc, Ib-oPc, la-Nc and Ib-Nc

(la-Nc) (Ib-Nc) and structural isomers of the compounds (la-Nc) and (Ib-Nc), where M is selected from Zn(ll), Cu(ll) and Pb(ll),

R ^a1 , R ^a2 , R ^a3 and R ^a4 have one of the meanings given for R ^a ; the substituent R ^a2 is attached in position 8 or 1 1 , the substituent R ^a3 is attached in position 15 or 18 and the substituent R ^a4 is attached in position 22 or 25.

Preference is given to compounds of the formulae la and lb, wherein R ^a , at each occurrence, is selected from phenyl, phenylthio, naphthyl, naphthyloxy, naphthylthio, anthracenyl, anthracenyloxy, anthracenylthio, oligothiophenyl or hetaryl, e.g. 5-, 6-, 8-, 9- or 10-membered hetaryl, containing 1 , 2 or 3 heteroatoms selected from the group consisting of O, N, Se and S as ring members. Phenyl, the phenyl moiety of phenylthio, naphthyl, the naphthyl moiety of naphthyloxy and naphthylthio, anthracenyl, the anthracenyl moiety of anthracenyloxy and anthracenylthio, the thiophenyl moieties of oligothiophenyl and hetaryl may each be unsubstituted or are substituted by 1 , 2, 3 or 4 substituents, independently selected from substituents R ^aa as defined above.

Hetaryl groups R ^a , containing 1 , 2 or 3 heteroatoms selected from the group consisting of O, N, and S as ring members, are preferably selected from 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 1 -pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 3-isothiazolyl, 4-isothiazolyl, 5-isothiazolyl, 3-pyrazolyl, 4-pyrazolyl, 5-pyrazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 1 -imidazolyl, 2-imidazolyl, 4-imidazolyl, 1 ,2,4-thiadiazol-3-yl, 1 ,2,4-thiadiazol-5-yl, 1 ,3,4-thiadiazol-

2- yl, 1 ,2,5-thiadiazol-3-yl, 1 ,2,3-thiadiazol-4-yl, 1 ,2,3-thiadiazol-5-yl, 1 ,2,4-triazol-3-yl, 1 ,3,4-triazol-2-yl, 2-thienothiophenyl, 3-thienothiophenyl, 2-benzo[b]thienyl,

3- benzo[b]thienyl, 2-benzofuryl, 3-benzofuryl, 2-thiazolothiazolyl or 1 ,3-benzothiazol- 2-yl.

More preference is given to compounds of the formulae la and lb, wherein R ^a , at each occurrence, is selected from phenyl, naphthyl, anthracenyl, oligothiophenyl and

5-membered sulphur containing hetaryl which may contain additionally 1 or 2 nitrogen atoms as ring members and may carry 1 or 2 fused-on arene rings and wherein phenyl, naphthyl, anthracenyl, oligothiophenyl and sulphur containing hetaryl are unsubstituted or substituted by 1 or 2 substituents R ^aa independently selected from Ci-Cio-alkyl, Ci-Cio-haloalkyl and halogen. Preferred meanings of R ^a are unsubstituted phenyl which is monosubstituted by

Ci-Cio-alkyl, 1 -naphthyl, oligohetaryl and 5-membered sulphur containing hetaryl which may contain additionally 1 or 2 nitrogen atoms as ring members and may carry a fused- on arene ring. If R ^a has the meaning of phenyl which is monosubstituted by Ci-Cio-alkyl, it is preferably selected from 4-methylphenyl, 4-ethylphenyl, 4-n-propylphenyl,

4- isopropylphenyl, 4-n-butylphenyl, 4-sec-butylphenyl, 4-tert-butylphenyl,

4-n-pentylphenyl; 4-neopentylphenyl, and 4-n-hexylphenyl. If R ^a has the meaning of oligohetaryl, it is preferably selected from 2,2'-bithiophenyl or 2-thienyl substituted by thienyl which for its part carries a Ci-Cio-alkyl group. Preferred oligohetaryl groups R ^a are e.g. 5'-(Ci-Cio-alkyl)-2,2'-bithiophenyl, more preferably 5'-(Ci-Cio-alkyl)-2,2'-bithiophen-5-yl, like 5'-n-hexyl-2,2'-bithiophen-5-yl. If R ^a has the meaning of a 5-membered sulphur containing hetaryl which may contain additionally 1 or 2 nitrogen atoms as ring members and may carry a fused-on arene ring it is preferably selected from 2-thienyl, 3-thienyl, thiazol-2-yl, thiazol-5-yl,

[1 ,3,4]thiadiazol-2-yl, benzo[b]thiophenyl, especially benzo[b]thiophen-2-yl.

Most preference is given to compounds of the formulae la and lb, wherein R ^a , at each occurrence, is selected from 2-thienyl, 5-(Ci-Cio-alkyl)-thiophen-2-yl, benzo[b]thiophen- 2-yl, 2,2'-bithiophen-5-yl, 5'-(Ci-Cio-alkyl)-2,2'-bithiophen-5-yl and 4-(Ci-Cio-alkyl)- phenyl. Those phthalocyanines show a remarkably high sensitivity to oxidizing gas,

In particular, in the formulae la and lb the group R ^a , at each occurrence, is selected from 2-thienyl, 5-methyl-thiophen-2-yl, 5-ethyl-thiophen-2-yl, 5-n-propyl-thiophen-2-yl, 5-isopropyl-thiophen-2-yl, 5-n-butyl-thiophen-2-yl, 5-sec-butyl-thiophen-2-yl, 5-tert- butyl-thiophen-2-yl, benzo[b]thiophen-2-yl, 2,2'-bithiophen-5-yl, 5'-methyl-2,2'- bithiophen-5-yl, 5'-ethyl-2,2'-bithiophen-5-yl, 5'-n-propyl-2,2'-bithiophen-5-yl,

5'-isopropyl-2,2'-bithiophen-5-yl, 5'-n-butyl-2,2'-bithiophen-5-yl, 5'-sec-butyl-2,2'- bithiophen-5-yl, 5'-tert-butyl-2,2'-bithiophen-5-yl, 5'-n-pentyl-2,2'-bithiophen-5-yl, 5'-n-hexyl-2,2'-bithiophen-5-yl, 4-methylphenyl, 4-ethylphenyl, 4-n-propylphenyl, 4-isopropylphenyl, 4-n-butylphenyl, 4-sec-butylphenyl, 4-tert-butylphenyl,

4-neopentylphenyl, 4-n-pentylphenyl and 4-n-hexylphenyl.

The substituent(s) R ^a may be located at any aromatic position of the fused arene ring A. In the case that the compounds of the formulae la and lb carry more than one substituent R ^a , they may be the same or different. Preferably, all substituents R ^a have the same meaning. Preferably, each ring A carries the same number of substituents R ^a . More preferably, all substituents R ^a have the same meaning and each ring A carries the same number of substituents R ^a . The index m in compounds of the formulae la and lb is preferably 0, 1 , 2, 3, 4, 5, 6, 7 or 8, more preferably 0, 4 or 8, in particular 0 or 4.

In the case that each A is a fused benzene ring, m is preferably 1 , 2, 3, 4, 5, 6, 7 or 8, more preferably 4 or 8. Each R ^a is preferably located at any of the two ortho-positions of the benzene ring. Most preference is given to those compounds of formulae la and lb, wherein each ring A is a benzene ring and each benzene ring carries one substituent R ^a in the ortho-position, i.e. m is 4. In the case that each A is a fused naphthalene ring, m is preferably 0, 1 , 2, 3, 4, 5, 6, 7 or 8, preferably 0, 4 or 8. If R ^a is present, preferably each R ^a is located at an inner position. In the case of the compounds of formulae la-2,3-Nc and lb-2,3-Nc, the inner positions are the positions 1 , 6, 10, 15, 19, 24, 28 and 33. In the case of the

compounds of formulae la-1 ,2-Nc and lb-1 ,2-Nc, the inner positions are the positions 1 , 2, 10, 1 1 , 19, 20, 28 and 29. One special embodiment are compounds of formulae la and lb, wherein each ring A is a naphthalene ring and each naphthalene ring carries one substituent R ^a in the inner position, i.e. m is 4. One further special embodiment are compounds of formulae la-Nc and Ib-Nc:

(la-Nc) (Ib-Nc)

The compounds (la-Nc) and (Ib-Nc) have structural isomers with regard to the position of the four naphthalene rings that shall also be encompassed by the formulae (la-1 ,2- Nc) and (lb-1 ,2-Nc). Those compounds may have the point groups D2h, C _s , C2v and C ₄ h. C ₄ h is the preferred isomer. The compounds (la-Nc) and (Ib-Nc) may be employed in pure form or in form of a mixture of at least two isomers. In the case that each A is a fused anthracene ring, m is preferably 1 , 2, 3, 4, 5, 6, 7 or 8, preferably 4 or 8. Preferably, each R ^a is located at an inner position. In the case of the compounds of formulae la-2,3-Ac and lb-2,3-Ac, the inner positions are the positions 1 , 2, 8, 9, 13, 14, 19, 20, 24, 25, 30, 31 , 35, 36, 41 and 42. Most preference is given to those compounds of formulae la and lb, wherein each ring A is an anthracene ring and each anthracene ring carries one substituent R ^a at the inner position, i.e. m is 4.

According to a further embodiment of the invention, particular preferred compounds of the formulae la and lb are the compounds of the formulae la-oPc and Ib-oPc, i.e. compounds of the formulae la-Pc and Ib-Pc, wherein the index m is 4 and the index n is 0,

(la-oPc) (Ib-oPc) where

M is selected from Zn(ll), Cu(ll) and Pb(ll),

R ^a1 , R ^a2 , R ^a3 and R ^a4 have one of the meanings given for R ^a ; wherein the substituent R ^a2 is attached in position 8 or 1 1 , the substituent R ^a3 is attached in position 15 or 18, and the substituent R ^a4 is attached in position 22 or 25.

In the compounds of the formulae la-oPc and Ib-oPc R ^a1 , R ^a2 , R ^a3 and R ^a4 are preferably independently of each other, selected from phenyl, phenyloxy, phenylthio, naphthyl, naphthyloxy, naphthylthio, anthracenyl, anthracenyloxy, anthracenylthio, oligothiophenyl and hetaryl, wherein hetaryl contains 1 , 2 or 3 heteroatoms selected from the group consisting of O, N, Se and S as ring members and wherein phenyl, the phenyl moiety of phenyloxy and phenylthio, naphthyl, the naphthyl moiety of naphthyloxy and naphthylthio, anthracenyl, the anthracenyl moiety of anthracenyloxy and anthracenylthio, the thiophenyl moieties of oligothiophenyl and hetaryl are each unsubstituted or substituted by 1 , 2, 3 or 4 substituents R ^aa .

In the compounds of the formulae la-oPc and Ib-oPc R ^a1 , R ^a2 , R ^a3 and R ^a4 are more preferably independently of each other, selected from phenyl, naphthyl, anthracenyl, oligothiophenyl and 5-membered sulphur containing hetaryl which may contain additionally 1 or 2 nitrogen atoms as ring members and may carry 1 or 2 fused-on arene rings and wherein phenyl, naphthyl, anthracenyl, oligothiophenyl and sulphur containing hetaryl are unsubstituted or substituted by 1 or 2 substituents R ^aa , independently selected from Ci-Cio-alkyl, Ci-Cio-haloalkyl and halogen.

In particular, the compounds of the formulae la-oPc and Ib-oPc R ^a1 , R ^a2 , R ^a3 and R ^a4 are independently of each other, selected from 2-thienyl, 5-(Ci-Cio-alkyl)-thiophen-2-yl, benzo[b]thiophen-2-yl, 2,2'-bithiophen-5-yl, 5'-(Ci-Cio-alkyl)-2,2'-bithiophen-5-yl and 4-(Ci-Cio-alkyl)-phenyl.

Preferably, R ^a1 , R ^a2 , R ^a3 and R ^a4 have the same definition. Examples of preferred compounds include:

2a: M

2b: M

2c: M

3 4a: M = Zn

4b: M = Cu

4c: M = Pb wherein in the compounds 3, 4a, 4b and 4c one 2-thienyl group is attached in position 8 or 1 1 , one 2-thienyl group is attached in position 15 or 18, and one 2-thienyl group is attached in position 22 or 25.

5 6a: M = Zn

6b: M = Cu

6c: M = Pb wherein in the compounds 5, 6a, 6b and 6c one benzo(b)thiophen-2-yl group is attached in position 8 or 1 1 , one benzo(b)thiophen-2-yl group is attached in position 15 or 18, and one benzo(b)thiophen-2-yl group is attached in position 22 or 25.

8a: M = Zn

8b: M = Cu

8c: M = Pb wherein in the compounds 7, 8a, 8b and 8c one 5'-n-hexyl-2,2'-bithiophen-5-yl group is attached in position 8 or 1 1 , one 5'-n-hexyl-2,2'-bithiophen-5-yl group is attached in position 15 or 18 and one 5'-n-hexyl-2,2'-bithiophen-5-yl group is attached in position 22 or 25.

10a: M = Zn

10b: M = Cu

10c: M = Pb wherein in the compounds 9, 10a, 10b and 10c one 4-n-propylphenyl group is attached in position 8 or 1 1 , one 4-n-propylphenyl group is attached in position 15 or 18, and one 4-n-propylphenyl group is attached in position 22 or 25. The sensors according to the invention are preferably employed for sensing oxidizing gases. The oxidizing gases are preferably selected from O3, O2, NO2, N2O4, H2O2, organic peroxides and halogens.

Preferably, the sensor according to the invention comprises electrodes configured to measure at least one electrical property of the at least one compound of the formulae la or lb.

In one embodiment, the invention regards a gas sensor, wherein the compounds of the formulae la or lb act as resistor. In this type of sensor, the principle of detection is merely based on the changes of resistance induced in the compounds of the formulae la or lb depending on the nature of the gas analytes brought into contact with the active material of the sensor (i.e. the compounds of the formulae la or lb). In other words, in this type of gas sensor the compounds of the formulae la or lb act as chemiresistor, i.e. a material that changes its electrical resistance in response to changes in the nearby chemical environment. Said sensor generally comprises at least two electrodes and at least one compound of the formulae la or lb arranged with respect to said electrodes to act as a resistor between said electrodes. In a preferred embodiment, a thin film of at least one compound of the formulae la or lb is employed to act as a resistor between the electrodes. Preferably, the thin film has a thickness of 30 to 350 nm, more preferably 50 to 300 nm. In a further embodiment, the invention regards a gas sensor, wherein the compounds of the formulae la or lb act as semiconductor. In this type of sensor, the principle of detection is based on the change of the semiconductor properties induced in the compounds of the formulae la or lb depending on the nature of the gas analytes brought into contact with the active material of the sensor (i.e. the compounds of the formulae la or lb). In other words, the conduction channel is affected in the presence of an analyte. These transistor type gas sensors have a structure that is similar to organic field effect transistors (OFETs). Said sensor comprises at least one gate electrode, at least one drain electrode and at least one source electrode and at least one compound of the formulae la or lb arranged with respect to said electrodes to act as a

semiconductor between said electrodes.

In a preferred embodiment, a thin film of at least one compound of the formulae la or lb is employed to act as a semiconductor between the electrodes. In this embodiment, the gas sensors have a structure that is similar to a thin film transistor (TFT). Preferably, the sensor comprises at least one gate electrode isolated from the at least one drain electrode and the at least one source electrode by a gate dielectric and wherein a thin film containing at least one compound of the formulae la or lb is arranged with respect to said gate, source and drain electrode(s) to act as a conduction channel in response to gate, source and drain potentials. Preferably, the thin film has a thickness of 3 to 200 nm, more preferably 5 to 150 nm.

According to a further aspect of the present invention there is provided a sensor system comprising: - a sensor chip having a plurality of sensors as defined above and in the following; a socket that mounts the sensor chip to a substrate and provides thermal and electrical interference isolation for the sensor chip; and

sensing circuitry mounted on the substrate for controlling sensing operations conducted by the plurality of sensors.

An example sensor system includes a plurality of sensors of the invention. In a preferred embodiment, a sensor chip having a plurality of sensors is mounted in a socket, for example by wire bonding. The socket provides thermal and electrical interference isolation for the sensor chip from associated sensing circuitry that is mounted on a common substrate, such as a PCB (printed circuit board). Suitable substrates are in principle the materials known for this purpose. Suitable substrates comprise, for example, semiconductors (e.g. doped Si, doped Ge), oxidic materials (such as glass, ceramics, S1O2, especially quartz), metals (preferably metals of groups 8, 9, 10 or 1 1 of the Periodic Table, such as Au, Ag, Cu), metal alloys (for example based on Au, Ag, Cu, etc.), semiconductor alloys, polymers (e.g. polyvinyl chloride, polyolefins, such as polyethylene and polypropylene, polyesters,

fluoropolymers, polyamides, polyimides, polyurethanes, polyethersulfones, polyalkyl (meth)acrylates, polystyrene and mixtures and composites thereof), inorganic solids (e.g. ammonium chloride), paper and combinations thereof. The substrates may be flexible or inflexible, and have a curved or planar geometry, depending on the desired use.

Suitable dielectrics, e.g. for the use as gate dielectric, are S1O2, polystyrene, poly-a- methylstyrene, polyolefins (such as polypropylene, polyethylene, polyisobutene), polyvinylcarbazole, fluorinated polymers (e.g. Cytop), cyanopullulans (e.g. CYMM), polyvinylphenol, poly-p-xylene, polyvinyl chloride, or polymers crosslinkable thermally or by atmospheric moisture. Suitable dielectrics can be employed in form of self- assembled layers. Suitable are also "self-assembled nanodielectrics", i.e. polymers which are obtained from monomers comprising SiCI functionalities, for example

ClsSiOSiCIs, CI ₃ Si-(CH ₂ )6-SiCI ₃ , CI ₃ Si-(CH ₂ )i2-SiCl3, and/or which are crosslinked by atmospheric moisture or by addition of water diluted with solvents (see, for example, Facchetti, Adv. Mater. 2005, 17, 1705-1725). In a suitable embodiment, a common silicon wafer can be employed as substrate and subjected to a surface treatment, e.g. a heat treatment in a furnace to oxidize at least a part of the surface to form an insulating silicon oxide layer on the substrate.

The substrate generally is supplied with electrodes. If the compound of the formulae la or lb acts as a resistor, the electrodes permit the resistance of the active region to be measured. If the compound of the formulae la or lb acts as a resistor, the electrodes (corresponding to gate, drain and source electrodes of an field effect transistor) permit the semiconducting behaviour to be measured. The electrodes can e.g. be localized on the substrate (for example deposited onto or embedded into a nonconductive layer on the dielectric). The substrate may additionally comprise conductive gate electrodes which are typically arranged below the dielectric top layer (i.e. the gate dielectric).

As mentioned before, an insulator layer (gate insulating layer, gate dielectric) can be present on at least one part of the substrate surface. The insulator layer comprises at least one insulator which is preferably selected from inorganic insulators, such as S1O2, silicon nitride (S13N4), etc., ferroelectric insulators, such as AI2O3, Ta20s, La20s, ΤΊΟ2, Y2O3, etc., organic insulators, such as polyimides, benzocyclobutene (BCB), polyvinyl alcohols, polyacrylates, etc., and combinations thereof.

Suitable materials for the electrodes are in principle electrically conductive materials. These include metals, preferably metals of groups 6, 7, 8, 9, 10 or 1 1 of the Periodic Table, such as Pd, Au, Ag, Cu, Al, Ni, Cr, etc. Also suitable are conductive polymers, such as PEDOT (= poly(3,4-ethylenedioxythiophene)):PSS (= poly(styrenesulfonate)), polyaniline, surface-modified gold, etc. Preferred electrically conductive materials have a specific resistance of less than 10 ^-3 ohm x meter, preferably less than 10 ^_4 ohm x meter, especially less than 10 ^-6 or 10 ^"7 ohm x meter.

In a specific embodiment, the electrodes are present at least partly on the compounds of the formulae la or lb. It will be appreciated that the substrate may comprise further components as used customarily in semiconductor materials or ICs, such as insulators, resistors, capacitors, conductor tracks, etc.

The electrodes may be applied by customary processes, such as evaporation or sputtering, lithographic processes or another structuring process, such as printing techniques.

The compounds la and lb may also be processed with suitable auxiliaries (polymers, surfactants) in disperse phase by printing.

In a first preferred embodiment, the deposition of at least one compound of the general formula la or lb is carried out by a gas phase deposition process (physical vapor deposition, PVD). This method is usually employed if the compound of the general formula la or lb has not a sufficient solubility in a solvent to allow wet processing. PVD processes are performed under high-vacuum conditions and comprise the following steps: evaporation, transport, deposition. The material deposited is obtained in high purity. In a specific embodiment, the deposited material is obtained in the form of crystals or comprises a high crystalline content. In general, for the PVD, at least one compound of the general formula la or lb is heated to a temperature above its evaporation temperature and deposited on a substrate by cooling below the

crystallization temperature. The temperature of the substrate in the deposition is preferably within a range from about 20 to 450°C, more preferably from 50 to 400°C. The resulting semiconductor layers generally have a thickness which is sufficient for forming a (semi)conducting channel which is in contact with the electrodes (in a FET the source/drain electrodes). The deposition can be effected under an inert

atmosphere, for example, under nitrogen, argon or helium. The deposition is effected typically at ambient pressure or under reduced pressure. A suitable pressure range is from about 10 ^"7 to 1 .5 bar.

The compound of the formulae la or lb is preferably deposited on the substrate in a thickness of from 3 to 350 nm.

In a second preferred embodiment, the deposition of at least one compound of the general formula la or lb is effected by spin-coating. Soluble compounds of the formulae la and lb are also suitable for producing sensor elements by a printing process. It is possible for this purpose to use customary printing or coating processes (inkjet, flexographic, offset, gravure; intaglio printing, nanoprinting, slot die). Preferred solvents for the use of compounds of the formulae la or lb are e.g. tetrahydrofuran, aromatic solvents, such as toluene, xylene, etc.

In a preferred embodiment, the active material is in form of a thin-film transistor (TFT). In a customary construction, a thin-film transistor has a gate electrode disposed on the substrate or buffer layer (the buffer layer being part of the substrate), a gate insulation layer disposed thereon and on the substrate, a semiconductor layer disposed on the gate insulator layer, an ohmic contact layer on the semiconductor layer, and a source electrode and a drain electrode on the ohmic contact layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a gas sensor 1 according to one exemplary embodiment of the present invention in a semiconductor array (transistor layout). The sensor 1 includes an active region 2 comprising at least one compound of the formula la or lb as

semiconductor material that is sensitive to the analytes, such as a gas analyte 8. In a special embodiment, the active region 2 is an organic thin film channel comprising at least one compound of the formulae la or lb. The gas sensor 1 further comprises a substrate 3, e.g. a silicon substrate. The gate dielectric 4, e.g. silicon dioxide, isolates source electrode 5 and drain electrode 6 and a gate electrode 7 is formed on an opposite side of the substrate 3.

FIG. 2 illustrates a gas sensor 1 according to another exemplary embodiment of the present invention in a chemiresistor array. The sensor 1 includes an active region 2 comprising at least one compound of the formulae la or lb that is sensitive to the analytes, such as a gas analyte 8. The gas sensor 1 further comprises a substrate 4, e.g. a Si/Si02 substrate and electrodes 5. FIG. 3 illustrates the response of a gas sensor of the invention according to example 1 based on phthalocyanine (B) to NO2.

FIG. 4 illustrates the response of a gas sensor of the invention according to example 2 based on phthalocyanine (D) to NO2.

FIG. 5 illustrates the response of a gas sensor of the invention according to example 3 based on phthalocyanine (D) to O3.

FIG. 6 illustrates the response of a gas sensor of the invention according to example 4 based on phthalocyanine (E) to NO2.

FIG. 7 illustrates the response of a gas sensor of the invention according to example 5 based on phthalocyanine (E) to O3. FIG. 8 illustrates the response of a gas sensor of the invention according to example 6 based on phthalocyanine (F) to NO2.

FIG. 9 illustrates the response of a gas sensor of the invention according to example 7 based on phthalocyanine (F) to O3.

FIG. 10 illustrates the response of a gas sensor of the invention according to example 8 based on phthalocyanine (G) to NO2.

FIG. 1 1 illustrates the response of a gas sensor of the invention according to example 9 based on phthalocyanine (H) to NO2.

FIG. 12 illustrates the response of a gas sensor of the invention according to example 10 based on phthalocyanine (I) to NO2. EXAMPLES

The following compounds la and lb were employed:

10

(H)

(I)

The compounds (A) to (I) were employed in form of a mixture of structural isomers as obtained by chemical synthesis. Unless stated otherwise, all further reagents and solvents were obtained from commercial suppliers and were used without further purification.

Phthalocyanine sensors: Sensors were prepared, comprising the afore-mentioned phthalocyanines as active layer for sensing oxidizing gas, such as NO2 or O3. Highly doped silicon wafers coated with a 30 nm layer of AI2O3 prepared by atomic layer deposition (ALD) were thoroughly cleaned by treatment with isopropanol dried at 100°C at ambient air on a hotplate for 10 min. The surface of the AI2O3 layer is treated by a brief exposure to an oxygen plasma. The substrate is then immersed into a 2-propanol solution of an alkyl phosphonic acid (0.34 mg/mL solution of

CioH2i PO(OH)2) which results in the formation of a self-assembled monolayer (SAM) on the surface. The highly doped silicon is used as substrate and back gate electrode, the alkyl phosphonic acid treated AI2O3 acts as the gate dielectric.

Gold contacts were evaporated through a shadow mask onto the silicon substrate to form an approximately 60 nm thick layer. In the case of unsoluble phthalocyanines, such as example A or B, a phthalocyanine film with a thickness of 60 nm was thermally evaporated at a temperature of approximately 400°C with an evaporation rate of about 1A s. In case of soluble phthalocyanine, a 2% (weight/weight) solution of the phthalocyanine in tetrahydrofuran was filtered through a 0.45 micrometer

poly-tetrafluoroethylene (PTFE) filter and then applied by spin coating (500 rpm, 30 seconds). The wet organic layer was dried at 80°C on a hot plate for 5 minutes. The sensors were doped in ambient air for at least 48 hours before testing.

The sensors were operated in a chemiresistor array as depicted in figure 2.

Measurement of chemiresistor sensing performance was done with a Keithley 4300- SCS semiconductor characterization system with applied voltage of 5V. Gas measurements have been carried out using dry synthetic air at a total air flow of 2 l/min at room temperature. The employed synthetic air was a mixture of 80% pure N2

(99.999% purity) and 20% pure 0 ₂ (99.999% purity). The synthetic air as well as the analyte (NO2 or O3) concentration has been adjusted by a computer-controlled gas mixing and flow control system. Determination of the detection limit:

The detection limit of gas sensors comprising a compound of the formulae la or lb as chemiresistor was determined. Chemiresistive phthalocyanine sensors of the compounds A to I were prepared as mentioned above. Table 1 shows the sensitivity behavior of the chemiresistors to NO2 or O3 as oxidizing gas. The sensors were brought into contact with gas samples of dry synthetic air containing a certain amount of analyte for a certain measurement period according to table 1 If no signal could be detected, the sensor was regenerated with pure dry synthetic air and the measurement repeated with a higher concentration of the analyte. This procedure was repeated until the lower limit of detection was reached. Table 1 shows the treshhold values for the chemiresistive phthalocyanine sensors according to the invention. The employed materials showed high sensitivity to oxidizing gas, such as NO2 and O3 with a lower limit of detection reaching 10 ppb (Example G) to NO2 and 20 ppb to O3 (Examples B, G).

Table 1 . Sensitivity behavior of selected materials

Td: decomposition temperature of the active material Performance evaluations: Example 1 (compound B)

Figure 3 shows the measured current in relation to the concentration of NO2 over the time at an applied voltage of 5V. The chemiresistor contains compound (B) as active material. During the period of the measurement, the chemiresistor was exposed to different concentration of the analyte NO2 with a concentration of 20, 50, 100, 150 and 200 ppb repeated for 2 cycles. The measured current shows a clear gradient change as the analyte was introduced at time T = 1000 s.

Even at the lowest concentration, a clear gradient change is clearly recognizable. The measured current showed a clear gradient change as the analyte gas was introduced at T = 1000 s. After the analyte exposure stopped, the measured current showed an opposite gradient change which corresponds to a recovery of the sensor in pure synthetic air. The exposure of oxidizing gases to the chemiresistor introduces a baseline shift which completely disappears after a suitable time of recovery. Immediate baseline recovery can be achieved if the sensor is heated. For the purpose of the present example, the test sensor was not equipped with a heater. Nevertheless, the example shows that the compounds employed according to the invention are suitable for use in gas sensors for oxidizing gases. Repeated measurement shows that a chemiresistor comprising compound (B) has a high sensitivity to NO2 with good reversibility and response time. It can be seen that the chemiresistor which comprised compound (B) is able to sense NO2 concentrations as low as 20 ppb.

Examples 2 and 3 (compound D):

Figure 4 (example 2) and figure 5 (example 3) show the measured current in relation to the concentration of NO2 (example 2) or O3 (example 3) over the time at an applied voltage of 5V. The chemiresistor contains compound (D) as active material. During the period of the measurement, the chemiresistor was exposed to different concentrations of the analyte (N0 ₂ or 0 ₃ ) with a concentration of 50, 60, 80, 100, 120 and 200 ppb repeated for 2 cycles. The measured current shows a clear gradient change as the analyte was introduced at time T = 125 s.

At lower concentrations, the increase in the gradient change of the current is correspondingly weaker compared to exposure to a high concentration of the analyte. However, even at the lowest concentration, a change in the gradient is clearly recognizable. After the analyte exposure stopped, the measured current showed a change of the gradient in the opposite direction which corresponds to a recovery of the sensor in pure synthetic air. The exposure of oxidizing gases to the chemiresistor introduces a baseline shift which completely disappears after a suitable time of recovery. Immediate baseline recovery can be achieved if the sensor is heated. For the purpose of the present examples, the test sensor was not equipped with a heater. Nevertheless, the examples show that the compounds employed according to the invention are suitable for use in gas sensors for oxidizing gases. Repeated

measurement shows that a chemiresistor comprising compound (D) has a high sensitivity to NO2 and O3 with good reversibility and response time. It can be seen that the chemiresistor which comprised compound (D) is able to sense NO2 or O3 concentrations as low as 50 ppb.

Examples 4 and 5 (compound E): Figure 6 (example 4) and figure 7 (example 5) show the measured current in relation to the concentration of NO2 (example 4) or O3 (example 5) over the time at an applied voltage of 5V. The chemiresistor contains compound (E) as active material. During the period of the measurement, the chemiresistor was exposed to different concentrations of the analyte (NO2 with a concentration of 20, 50, 100, 150 and 200 ppb and O3 with a concentration of 50, 60, 80, 100, 120 and 200 ppb) repeated for 2 cycles. The measured current shows a clear gradient change as the analyte was introduced.

The examples show that the compound (E) employed according to the invention is suitable for use in gas sensors for oxidizing gases. Repeated measurements show that a chemiresistor comprising compound (E) has a high sensitivity to NO2 and O3 with good reversibility and response time. It can be seen that the chemiresistor which comprises compound (E) is able to sense NO2 at concentrations as low as 50 ppb or O3 at concentrations as low as 50 ppb.

Examples 6 and 7 (compound F):

Figure 8 (example 6) and figure 9 (example 7) show the measured current in relation to the concentration of NO2 (example 6) or O3 (example 7) over the time at an applied voltage of 5V. The chemiresistor contains compound (F) as active material. During the period of the measurement, the chemiresistor was exposed to different concentrations of the analyte (NO2 with a concentration of 20, 50, 100, 150 and 200 ppb and O3 with a concentration of 50, 60, 80, 100, 120 and 200 ppb) repeated for 2 cycles. The measured current shows a clear gradient change as the analyte was introduced.

The examples show that the compound (F) employed according to the invention is suitable for use in gas sensors for oxidizing gases. Repeated measurements show that a chemiresistor comprising compound (F) has a high sensitivity to NO2 and O3 with good reversibility and response time. It can be seen that the chemiresistor which comprises compound (F) is able to sense NO2 at concentrations as low as 20 ppb or O3 at concentrations as low as 50 ppb.

Example 8 (compound G): Figure 10 shows the sensing behaviour of a chemiresistor comprising compound (G) to NO2. During the period of the measurement, the chemiresistor was exposed to NO2 with varied concentration of 10 to 200 ppb repeated for 2 cycles. The chemiresistor shows a good response, reversibility and response time to NO2 with a lower limit of detection of 10 ppb.

Example 9 (compound H):

Figure 1 1 shows the sensing behaviour of a chemiresistor comprising compound (H) to NO2. During the period of the measurement, the chemiresistor was exposed to NO2 with varied concentration of 20, 50, 100, 150 and 200 ppb repeated for 2 cycles. The chemiresistor shows a good response, reversibility and response time to NO2 with a lower limit of detection of 20 ppb. Example 10 (compound I):

Figure 12 shows the sensing behaviour of a chemiresistor comprising compound (I) to NO2. During the period of the measurement, the chemiresistor was exposed to NO2 with varied concentration of 50, 60, 80, 100, 120 and 200 ppb repeated for 2 cycles. The chemiresistor shows a good response, reversibility and response time to NO2 with a lower limit of detection of 50 ppb.