SUBJECT MATTER OF THE INVENTION

The present invention relates to compounds of the tetraarylbenzidine-type, bearing specific (het)aryl groups at the nitrogen atoms bound to the 1 ,1 '-biphenylene backbone, and to methods for their preparation. The invention further relates to the use of the tetraarylbenzidine derivatives in organic electronics, in particular as hole transport material (HTM) or electron blocking material (EBM).

BACKGROUND OF THE INVENTION

"Organic electronics" is concerned principally with the development, characterization and application of new materials and manufacturing processes for the production of electronic components based on organic small molecules or polymers with desirable electronic properties. These include in particular organic field-effect transistors (OFETs), like organic thin-film transistors (OTFTs), organic electroluminescent devices like organic light-emitting diodes (OLEDs), organic solar cells (OSCs), e.g. excitonic solar cells, dye sensitized solar cells (DSSCs) or Perovskite solar cells, electrophotography, in particular photoconductive materials in an organic photoconductor (OPC), organic optical detectors, organic photoreceptors, organic field-quench devices (OFQDs), light-emitting electrochemical cells (LECs) and organic laser diodes. Such organic semiconductive materials can be formed either from compounds with good electron donor properties (p-conductors) or from compounds with good electron acceptor properties (n-conductors). In contrast to inorganic semiconductors, organic semiconductors have a very low intrinsic charge carrier concentration. Organic semiconductor matrix materials are therefore usually doped in order to achieve good semiconductor properties.

"Organic photovoltaics" denotes the direct conversion of radiative energy, principally solar energy, to electrical energy using organic components. In contrast to inorganic solar cells, the light does not directly generate free charge carriers in organic solar cells, but rather excitons are formed first, i.e. electrically neutral excited states in the form of electron-hole pairs. These excitons can be separated at suitable photoactive interfaces (organic donor-acceptor interfaces or interfaces to an inorganic semiconductor). For this purpose, it is necessary that excitons which have been generated in the volume of the organic material can diffuse to this photoactive interface. The diffusion of excitons to the active interface thus plays a critical role in organic solar cells. There is a great demand for the development of materials which have maximum transport widths and high mobilities for light-induced excited states (high exciton diffusion lengths) and which are thus advantageously suitable for use as an active material in so-called excitonic solar cells.

It is known that certain organic compounds comprising two diarylamino groups bound to a bridging (hetero )arylene group are suitable for the use in organic electronic applications. JP 2009158535 A describes an organic light-emitting device (OLED) having high efficiency and long service life, comprising a hole injection layer 3 that contains aryl amine polymers, inter alia of the formulae (A1 ) and (A2)

EP 0879868 A2 describes organic compounds of the general formula (B) wherein X is a substituted or unsubstituted arylene group or a substituted or unsubstituted heterocyclic group and at least two of the Ar ¹ , Ar ² , Ar ³ , and Ar ⁴ groups are a substituted or unsubstituted fluorenyl group, and the remainder represents a substituted or unsubstituted aryl group. Dependinding on the types of substituent groups, those compounds can be used inter alia as hole transport materials to provide electroluminescent devices showing versatility of wavelenths and high durability. The groups X and Ar ¹ , Ar ² , Ar ³ , and Ar ⁴ can be selected from a plethora of different groups. In the sense of this application, the definition of aryl groups also encompasses heterocyclic groups without giving a concrete example. There is not the least incentive for a person skilled in the art that e.g. compounds (B) that bear heterocyclic groups that have only one single nitrogen atom or nitrogen atom group (like pyridyl) generally show conductivities that still need improvement.

WO 2017/097924 describes naphthoindacenodithiophenes (NDTs) and NDT- containing polymers of the general formula (C)

and the use of the polymers as semiconducting material.

DE 10 2012 104 118 A1 describes an optoelectronic device, comprising an organic layer, comprising a compound of the formula (D) wherein

An-An? are independently of each other substituted or unsubstituted homocycles or heterocycles, selected from phenyl, carbazol, fluorene, spirobifluorene, diphenylether, selenophene, furane, thiophen, pyrrole or phosphole, a-q are independently of each other 0 or 1 with the proviso that a + b + (...) + p + q > 6, wherein in at least one position a unit of two neighbouring Ar groups of the formula (E) (E) is present, where X is selected from N-R3, O, P-R3, S or Se, where R3 are independently of each other H, alkyl or aryl and

R, R1 , R2 independently of each other are H, alkyl, alkoxy or thioalkyl, where R1 and R2 are not both H.

KR 2011 0057078 A desribes heteroaryl amine compounds of the formula (F)

U * (Rs)n U

Heti Het ₂

Ri R ₂

(F) wherein

Ar is a substituted or unsubstituted biphenyl group, substituted or unsubstituted fluorenyl group or substituted or unsubstituted tetrahydropyrenyl group,

R1-R3 are selected from the group consisting of hydrogen, deuterium, halogen, cyano, substituted or unsubstituted C1-20 alkyl, substituted or unsubstituted Ce-4o aryl, substituted or unsubstituted C3-20 heteroaryl, substituted or unsubstituted C1.24 alkylsilyl and substituted or unsubstituted Ce-40 arylsilyl, n is an integer of 0-20, and

Heti and Het2 are substituted or unsubstituted C3-20 heteroaryl groups.

The compounds (F) can be used in an electron transport layer between the anode and the cathode of organic electroluminescent devices. This document does not disclose compounds of the tetraarylbenzidine-type, bearing two fluorenyl-type groups at the nitrogen atoms bound to an 1 ,1 '-biphenylene backbone.

KR 2016 0116220 A describes structures of the general formula (G)

Ari Ar ³

N wherein an amine group is bonded to indole or carbazole, that have good solubility in organic solvents and enable solution processing, and can be used as a hole transport layer or light emitting auxiliary layer material in organic electric devices. In particular A and B are wherein Ar ¹ to Ar ⁶ are each independently Ce-Ceo aryl, fluorenyl, a C2-C60 heterocyclic group containing at least one heteroatom selected from O, N, S, Si and P, a fused C3-C60 aliphatic ring system, a fused Ce-Ceo aromatic ring system, etc., provided that at least one of the Ar ¹ to Ar ⁶ groups is a crosslinking group selected from vinyl groups, acryloyl groups, methacyloyl groups, cyclic ethers, siloxanes, styrenes, trifluorovinyl ethers, benzocyclobutenes, cinnamates, chaicones, and oxetanes. As an intermediate in the synthesis of those compounds the following chlorine containing compound (H) is described

There is no indication to employ a chlorine-free derivative of (H) for organic electronic applications.

There is an ongoing demand for new organic compounds for organic electronic applications. They should be available by effective and economic synthetic routes. In particular, they should have lower molecular weights than compound known from the prior art, being capable of sublimation and/or possess good electronic application properties. Furthermore, they should be characterized by a good thermal stability and a high glass transition temperature.

It has now been found that, surprisingly, the tetraarylbenzidine-type compounds of the invention are advantageously suitable as hole conductors (p-semiconductors, electron donors) in organic photovoltaics. They are also especially suitable as electron blocking material (EBM).

SUMMARY OF THE INVENTION

A first object of the invention is a compound of the general formula (I) and mixtures thereof, wherein both R ^A groups have the same meaning and are selected from unsubstituted or substituted heterocyclic groups, comprising one or more rings wherein at least one ring is aromatic, wherein the heterocyclic group comprises as ring members 1 , 2, 3, 4 or more heteroatoms or heteroatom containing groups, selected from O, S, N and NR ^d , wherein the substituents R ^d in each case are independently of one another selected from hydrogen, straight-chain or branched C C4-alkyl, phenyl, 1- naphthyl, 2-naphthyl, 1 -fluorenyl, 2-fluorenyl, 3-fluorenyl, 4-fluorenyl, 1- carbazolyl, 2-carbazolyl, 3-carbazoly and 4-carbazolyl, wherein phenyl, 1- naphthyl, 2-naphthyl, 1 -fluorenyl, 2-fluorenyl, 3-fluorenyl, 4-fluorenyl, 1- carbazolyl, 2-carbazolyl, 3-carbazolyl and 4-carbazolyl are unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci- C4-alkyl and Ci-C4-alkoxy, with the proviso that if the heterocylic group comprises only one heteroatom or heteroatom containing group, this is O or S, and if the heterocylic group comprises more than one heteroatom or heteroatom containing groups, at least one of the heteroatoms or heteroatom containing groups is different from N and NR ^d ,

R ¹ , R", R ¹ " and R ^IV are independently selected from hydrogen, phenyl and C1-C4- alkyl, wherein R ¹ and R ¹ " have the same meaning and R" and R ^IV have the same meaning,

R ^1a and R ^1b independently of one another, are selected from hydrogen, straightchain or branched Ci-Ce-alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl. where R ^1a and R ^1b may also together form an alkylene group (Cl-kX with r being 4 A further object of the invention is the use of at least one compound of the general formula (I) as defined above and in the following as a hole transport material (HTM) in organic electronics, as an electron blocking material (EBM) in organic electronics, in organic solar cells (OSCs), solid-state dye sensitized solar cells (DSSCs) or Perovskite solar cells, in particular as a hole transport material in organic solar cells, as replacement of the liquid electrolyte in dye sensitized solar cells, as a hole transport material in Perovskite solar cells, in organic light-emitting diodes (OLEDs), in particular for displays on electronic devices and lighting.

A further object of the invention is an electroluminescent arrangement, comprising an upper electrode, a lower electrode, wherein at least one of said electrodes is transparent, an electroluminescent layer and optionally an auxiliary layer, wherein the electroluminescent arrangement comprises at least one compound of the formula (I), as defined above or in the following.

Preferably, the electroluminescent arrangement comprises at least one compound of the formula (I) in a hole-transporting layer or in an electron blocking layer.

In a preferred embodiment, the electroluminescent arrangement is an organic lightemitting diode (OLED).

A further object of the invention is an organic solar cell, comprising: a cathode, an anode, one or more photoactive regions comprising at least one donor material and at least one acceptor material in separate layers or in form of a bulk heterojunction layer, optionally at least one further layer selected from exciton blocking layers, electron conducting layers and hole transport layers, wherein the organic solar cell comprises at least one compound of the formula (I) as defined above or in the following.

A further object of the invention is a process (in the following denoted as "Route 1") for the preparation of a compound of the formula (I), comprising the steps a11 ) providing a compound of the formula (II. a11 ) (Il.a11) wherein

X is Cl, Br, I, CH ₃ SO ₃ , CF ₃ SO ₃ , CH ₃ -C ₆ H ₄ -SO ₃ or C ₆ H ₅ -SO _3>

R ^1a and R ^1b are defined as above and in the following, b11 ) reacting the compound of the formula (ll.al 1 ) with an aromatic amine of the formula (III. b11)

R ^A -NH ₂ (lll.bl 1 ) wherein R ^A is defined as above and in the following, in the presence of a palladium complex catalyst and a base to give (VI), or a12) providing an aromatic amine of the formula (IV.a12) wherein

R ^1a and R ^1b are defined as above and in the following, b12) reacting the aromatic amine of the formula (IV.a12) with a compound of the formula (V.b12)

R ^A -X (V.b12) wherein

R ^A is defined as above and in the following,

X is Cl, Br, I, CH ₃ SO ₃ , CF ₃ SO ₃ , CH ₃ -C ₆ H ₄ -SO ₃ or C ₆ H ₅ -SO ₃ , in the presence of a palladium complex catalyst and a base, to obtain a compound (VI) b) reacting the compound of the formula (VI) with a compound of the formula (VII) wherein

X is Cl, Br, I, CH3SO3, CF3SO3, CH3-C6H4-SO3 or C ₆ H ₅ -SO ₃₎

R ¹ , R", R ¹ " and R ^IV are as defined above and in the following, in the presence of a palladium complex catalyst and a base to obtain a compound (I).

A further object of the invention is a process (in the following denoted as "Route 2") for the preparation of a compound of the formula (I), comprising the steps a2) providing a compound of the formula (VII) wherein

X is Cl, Br, I, CH3SO3, CF3SO3, CH3-C6H4-SO3 or C ₆ H5-SO ₃ , R ¹ , R", R ¹¹¹ and R ^IV are as defined above and in the following, b2) reacting the compound of the formula (VII) with an aromatic compound of the formula (VIII)

R ^A -NH ₂ (VIII) wherein

R ^A is defined as above and in the following, in the presence of a palladium complex catalyst and a base to obtain a compound of the formula (IX) c2) reacting the compound of the formula (IX) with a compound of the formula (Il.a11) wherein

X is Cl, Br, I, CH3SO3, CF3SO3, CH3-C ₆ H ₄ -SO ₃ or C ₆ H ₅ -SO ₃ ,

R ^1a and R ^1b are defined as above and in the following, in the presence of a palladium complex catalyst and a base to obtain a compound (I).

A further object of the invention is a process (in the following denoted as "Route 3") for the preparation of a compound of the formula (I), comprising the steps a3) providing a compound of the formula (X) wherein

R ¹ , R", R" ¹ and R ^IV are independently selected from hydrogen and Ci-C ₄ -alkyl, wherein R ¹ and R ¹ " have the same meaning and R" and R ^IV have the same meaning,

R ^1a and R ^1b independently of one another, are selected from hydrogen, straightchain or branched Ci-Ce-alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl, where R ^1a and R ^1b may also together form an alkylene group (CH2) _r with r being 4 or 5, b3) reacting the compound of the formula (X) with a compound of the formula (V.b12)

R ^A -X (V.b12) wherein

X is Cl, Br, I, CH3SO3, CF3SO3, CH3-C6H4-SO3 or C ₆ H ₅ -SO ₃ , in the presence of a palladium complex catalyst and a base, to obtain a compound (I).

DETAILED DESCRIPTION OF THE INVENTION

The compounds of the general formula (I) and the methods for their preparation have at least one of the following advantages:

The compounds of the formula (I) are characterized by a good thermal stability and environmental stability.

Generally, compounds (I) have a high glass transition temperature. They are usually sublimable and allow the fabrication of devices by physical vapor deposition. The compounds of the formula (I) are in particular suitable as organic semiconductors. Preferred applications of the compounds (I) are as hole transport material (HTM) or electron blocking material (EBM).

Surprisingly, the tetraarylbenzidine-type compounds of the invention are advantageously suitable as hole conductors (p-semiconductors, electron donors) in organic photovoltaics. For example, the material from example 10 of this invention displays a glass temperature of 159.5 °C, is amorphous (XRD) and and shows at similar concentrations of NDP-9 a significantly higher conductivity as the known material (EP0879868 A2) of example 7.

The invention further allows providing compounds of the formula (I), where the size of the semiconductor band gap is adjusted to very effectively utilize the solar light.

The processes of the invention allow a very effective and economic synthesis of a great variety of compounds of the formula (I). Thus, it is possible to easily provide a compound (I) with optimized properties for the intended use.

It is noted that in the formulae depicted herein, a methyl group may be indicated as a solid line. Thus, for example, the following formulae are two alternatives to depict the same compound

It is also noted that in general hydrogen atoms are not depicted in a formula, unless the formula clearly dictates otherwise. In other words, in some specific formulae of this application the hydrogen atoms are explicitely shown but in most cases not, as is the usual practice. Correspondingly, the definition that an aromatic ring, e.g. a benzene ring, may be substituted by 0 to x substituents means that ring atoms that are capable of being substituted but that do not bear a substituent bear hydrogen atoms instead.

As used in this specification and the claims, the singular form "a", "an", and "the" include plural forms unless the context clearly indicates otherwise.

The definitions of the variables specified in the above formulae use collective terms which are generally representative of the respective substituents. The definition Cn-Cm gives the number of carbon atoms possible in each case in the respective substituent or substituent moiety.

The expression "halogen" denotes in each case fluorine, bromine, chlorine or iodine, particularly chlorine, bromine or iodine. Similarly, the term "halo" denotes in each case fluoro, chloro, bromo or iodo.

The term "unbranched" as used herein is also referred to as linear or straightchain.

The term "C _n -Cm-alkyl" as used herein refers to a branched or unbranched saturated hydrocarbon group having n to m carbon atoms, e.g. 1 to 2 ("Ci-C2-alkyl"), 1 to 4 ("Ci-C4-alkyl") or 1 to 6 ("Ci-Ce-alkyl"). Ci-C ₂ -Alkyl is methyl or ethyl. Examples for Ci-C4-alkyl are, in addition to those mentioned for Ci-C2-alkyl, propyl, isopropyl, butyl, 1 -methylpropyl (sec-butyl), 2-methylpropyl (isobutyl) or 1 ,1 -dimethylethyl (tert-butyl). Examples for Ci-Ce-alkyl are, in addition to those mentioned for Ci-C4-alkyl, pentyl, 1 -methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1 -ethyl propyl,

1.1 -dimethylpropyl, 1 ,2-dimethylpropyl, hexyl, 1 -methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1 ,1 -dimethylbutyl, 1 ,2-dimethylbutyl, 1 , 3-d i methyl butyl,

2.2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1 -ethylbutyl, 2-ethylbutyl,

1 .1 .2-trimethylpropyl, 1 ,2,2-trimethylpropyl, 1-ethyl-1 -methylpropyl, or 1-ethyl-2- methylpropyl.

Similarly, the term "C _n -C _m -alkoxy" refers to straight-chain or branched alkyl groups having n to m carbon atoms, e.g. 1 to 2 carbon atoms or 1 to 4 carbon atoms (as mentioned above) attached via an oxygen atom at any bond in the alkyl group to the remainder of the molecule. Ci-C2-Alkoxy is methoxy or ethoxy. Examples for C1-C4- alkoxy are, in addition to those mentioned for Ci-Ca-alkoxy, n-propoxy, 1 -methylethoxy (isopropoxy), butoxy, 1 -methylpropoxy (sec-butoxy), 2-methylpropoxy (isobutoxy) or 1 ,1 -dimethylethoxy (tert-butoxy).

The term "C _n -C _m -cycloalkyl" as used herein refers to a monocyclic n- to m- membered saturated cycloaliphatic radical having, e.g. 3 to 8 carbon atoms. Examples for Cs-Cs-cycloalkyl are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.

Similarly, the term "C _n -Cm-cycloalkoxy" refers to a monocyclic n- to m-membered saturated cycloaliphatic radical, e.g. Cs-Cs-cycloalkyl (as mentioned above) bonded through O linkage to the skeleton.

The term "aryl" as used herein refers to monocyclic, bicyclic, tricyclic and tetracyclic aromatic hydrocarbon radicals with 6 to 18 ring carbon atoms, in which the rings are all condensed (fused) or two of the aromatic rings may also be joined to one another by a chemical bond and a divalent radical selected from -CH2-, -O-, -S- or -N(H)-. Examples include phenyl, naphthyl, anthracenyl, phenanthrenyl, fluorenyl, dibenzofuranyl (dibenzofuryl), dibenzothienyl, carbazolyl, 11 H-benzo[b]fluorenyl, naphtho[2,3-b]benzofuryl, naphtho[2,3-b]benzothienyl and 5H-benzo[b]carbazolyl. Aryl may be substituted at one, two, three, four, more than four or all substitutable positions. Suitable substituents are in general Ci-Ce-alkyl, Ci-C4-alkoxy, carbazol-9-yl (N-bound carbazolyl), which is unsubstituted or substituted by Ci-C4-alkyl, Ci-C4-alkoxy and phenyl, wherein phenyl on its part may be substituted by 1 , 2, 3 or 4 different or identical substituents selected from Ci-C4-alkyl and Ci-C4-alkoxy. In addition, suitable substituents attached at aryl are in general also diphenylamino, Cs-Cs-cycloalkyl, phenyl, biphenylyl, terphenylyl, naphthyl, anthracenyl and phenanthryl, wherein each of the cyclic rings in the eight last-mentioned groups are unsubstituted or substituted by 1 , 2, 3, 4 or 5 different or identical substituents selected from Ci-C4-alkyl, Ci-C4-alkoxy and carbazol-9-yl which is unsubstituted or substituted by Ci-C ₄ -alkyl, Ci-C4-alkoxy and phenyl, wherein phenyl on its part may be substituted by 1 , 2, 3 or 4 different or identical substituents selected from Ci-C4-alkyl and Ci-C4-alkoxy. In addition, two substituents bonded to the same carbon atom of fluorenyl or 11 H-benzo[b]fluorenyl, together may form an alkylene group (CH2)r with r being 4, 5, 6 or 7 thus forming a 5- to 8-membered saturated carbocycle, in which 1 or 2 hydrogen atoms in this group may be replaced by a group Ci- -alkyl or Ci-C4-alkoxy or two substituents bonded to the same carbon atom of fluorenyl or 11 H-benzo[b]fluorenyl together may form an alkylene group (CH2) _r with r being 4, 5, 6 or 7 thus forming a 5- to 8-membered saturated carbocycle, which may be benz-annelated with one or two benzene groups, where the benzene ring(s) is (are) optionally substituted by 1 , 2, 3 or 4 identical or different C1-C4- alkyl or Ci-C4-alkoxy.

The term "heterocyclic group containing at least one aromatic ring" denotes monocyclic and polycyclic ring systems containing at least one aromatic ring, wherein the ring system comprises as ring members 1 , 2, 3, 4 or more heteroatoms or heteroatom containing groups, selected from O, S, N and NR ^d , wherein the substituents R ^d in each case are independently of one another selected from hydrogen, straight-chain or branched Ci-C4-alkyl, straight-chain or branched Ci-C4-alkoxy, phenyl, 1 -naphthyl, 2-naphthyl, 1 -fluorenyl, 2-fluorenyl, 3-fluorenyl, 4-fluorenyl, 1-carbazolyl, 2- carbazolyl, 3-carbazoly and 4-carbazolyl, wherein phenyl, 1-naphthyl, 2-naphthyl, 1- fluorenyl, 2-fluorenyl, 3-fluorenyl, 4-fluorenyl, 1-carbazolyl, 2-carbazolyl, 3-carbazoly and 4-carbazolyl are unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl and Ci-C4-alkoxy.

Preferred are monocyclic, bicyclic, tricyclic and tetracyclic ring systems with a total of 5 to 30 ring atoms, in which the rings are all condensed (fused) or two of the rings may also be joined to one another by a chemical bond or a divalent radical selected from -CH2-, -O-, -S- and -N(H)-.

Preferred are monocyclic heteroaromatic 5- to 8-membered rings, more preferably 5- or 6-membered rings, comprising as ring members 1 , 2, 3 or 4 heteroatoms selected from N, O and S.

Preferred are also bicyclic, tricyclic and tetracylic ring systems, comprising 1 , 2, 3 or 4 rings selected from saturated, partially unsaturated, or fully unsaturated carbocycles and heterocycles with the proviso that 1 , 2, 3 or 4 of the rings are aromatic. In this context, the term “heterocycle” includes preferably 5- to 8-membered, more preferably 5- to 7-membered, in particular 5- or 6-membered, monocyclic heterocyclic rings. The heterocycles may be saturated, partially unsaturated, or fully unsaturated. The term “fully unsaturated” also includes “aromatic”. In a preferred embodiment, a fully unsaturated heterocycle is thus an aromatic heterocycle, preferably a 5- or 6-membered aromatic heterocycle comprising one or more, e.g. 1 , 2, 3, or 4, preferably 1 , 2, or 3 heteroatoms selected from N, O and S as ring members. Non-aromatic heterocyles usually comprise 1 , 2, 3 or 4, preferably 1 , 2 or 3 heteroatoms or heteroatom containing groups, selected from O, S, N and NR ^d as ring members, preferably selected from N, O and S as ring members.

If a moiety is described as being "optionally substituted", the moiety may be either unsubstituted or substituted.

If a moiety is described as "substituted", a non-hydrogen radical is in the place of hydrogen radical of any substitutable atom of the moiety. If there are more than one substitution on a moiety, each non-hydrogen radical may be identical or different unless otherwise stated.

Preferred compounds according to the invention are compounds of the formula (I), wherein R ^1a and R ^1b are independently of one another selected from hydrogen and straight-chain or branched Ci-C ₄ -alkyl. More preferably, R ^1a and R ^1b are independently of one another selected from hydrogen, methyl and ethyl.

In preferred embodiment, both radicals R ^1a in formula (I) have the same meaning. In a further preferred embodiment, both radicals R ^1b in formula (I) have the same meaning. Especially, all radicals R ^1a and R ^1b in formula (I) have the same meaning.

In a first preferred embodiment, all radicals R ^1a and R ^1b in formula (I) are hydrogen. In a second preferred embodiment, all radicals R ^1a and R ^1b in formula (I) are methyl. In a third preferred embodiment, all radicals R ^1a and R ^1b in formula (I) are phenyl.

R', R", R ¹ " and R ^IV are independently selected from hydrogen, Ci-C4-alkyl and Cr C4-alkoxy. Preferably, R ¹ , R", R ¹¹¹ and R ^IV are independently selected from hydrogen, Ci-C ₂ -alkyl and Ci-C2-alkoxy.

In particular, the substituents R ¹ , R", R ¹ " and R ^IV are selected from the definitions given in one line of the following table

In a special embodiment R ¹ , R", R ¹ " and R ^IV are all hydrogen.

Preferably, the compound of the formula (I) is selected from compounds (LA),

wherein both R ^A groups have the same meaning and are selected from unsubstituted or substituted heterocyclic groups.

Preferably the R ^A groups are selected from groups of the formulae (AR-I) to (AR-XCV)

(AR-XIX) (AR-XX) (AR-XXI) (AR-XXII) (AR-XXIII)

(AR-XLIV) (AR-XLV) (AR-XLVI)

wherein

# in each case denotes the bonding site to the nitrogen atom; x is 0, 1 or 2; y1 is 0, 1 or 2; y2 is 0, 1 or 2; y3 is 0, 1 or 2;

R ² independently of one another are selected from straight-chain or branched C1-C4- alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl, phenyl, tolyl, xylyl and mesityl;

R ³ independently of one another are selected from straight-chain or branched C1-C4- alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl, phenyl, tolyl, xylyl and mesityl;

R ⁴ is selected from straight-chain or branched Ci-C4-alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl, phenyl, tolyl, xylyl and mesityl;

R ⁵ independently of one another are selected from straight-chain or branched C1-C4- alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl, phenyl, tolyl, xylyl and mesityl; in formulae AR-LXXXVIII, AR-LXXXIX, AR-XC, AR-XCI, AR-XCII and AR-XCIII: R ²³ , R ²⁴ , R ²⁵ and R ²⁶ , if present, independently of one another, are selected from hydrogen, straight-chain or branched Ci-C4-alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl, R ^e is hydrogen or Ci-Ce-alkyl, and

R ^f is hydrogen or Ci-Cs-alkyl; in formulae AR-XCIV and AR-XCV:

R ²¹ , R ²³ , R ²⁴ , R ²⁵ , R ²⁶ , R ²⁷ , R ²⁸ , R ^29a and R ^29b , if present, independently of one another, are selected from hydrogen, straight-chain or branched Ci-C4-alkyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C4-alkyl, where R ^29a and R ^29b together may also form an alkylene group (CH2)r with r being 4, 5 or 6.

In formulae AR-I to AR-XX, each radical R ² is preferably selected from methyl, ethyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 or 2 different or identical substituents selected from methyl, ethyl, phenyl, tolyl, xylyl and mesityl.

In formulae AR-XXI to AR-LI, AR-LIII, AR-LIV, AR-LXVIII, AR-LXIX and AR-LXX each radical R ³ is preferably selected from methyl, ethyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 or 2 different or identical substituents selected from methyl, ethyl, phenyl, tolyl, xylyl and mesityl.

In formulae AR-XXXIII, AR-XXXV, AR-LII and AR-LXI to AR-LXVII, radical R ⁴ is preferably selected from methyl, ethyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 or 2 different or identical substituents selected from methyl, ethyl, phenyl, tolyl, xylyl and mesityl.

In formulae AR-LV to AR-LX, each radical R ⁵ is preferably selected from methyl, ethyl and phenyl, wherein phenyl is unsubstituted or substituted by 1 or 2 different or identical substituents selected from methyl, ethyl, phenyl, tolyl, xylyl and mesityl.

The value for y1 is preferably 0 or 1.

The value for y2 is preferably 0 or 1 .

The value for y3 is preferably 0 or 1 .

In formulae AR-LXXXVIII to AR-XCIII, each R ²³ , R ²⁴ , R ²⁵ and R ²⁶ , if present, is selected from hydrogen, Ci-Cz-alkyl, Ci-C2-alkoxy, phenyl, 1 -naphthyl, 2-naphthyl, 9- fluorenyl and 9-carbazolyl, wherein phenyl, 1 -naphthyl, 2-naphthyl, 9-fluorenyl or 9- carbazolyl are unsubstituted or substituted by 1 , 2 or 3 different or identical substituents selected from Ci-C2-alkyl and Ci-C ₂ -alkoxy, R ^e is hydrogen or methyl, and

R ^f is hydrogen or methyl.

In formulae AR-XCIV and AR-XCV, each radical R ²¹ , R ²³ , R ²⁴ , R ²⁵ , R ²⁶ , R ²⁷ , R ²⁸ , R ^29a and R ^29b , if present, is selected from hydrogen, Ci-C2-alkyl, Ci-C2-alkoxy, phenyl, 1 -naphthyl, 2-naphthyl, 1 -fluorenyl, 2-fluorenyl, 3-fluorenyl, 4-fluorenyl, 1-carbazolyl, 2- carbazolyl, 3-carbazoly and 4-carbazolyl, wherein phenyl, 1 -naphthyl, 2-naphthyl, 1- fluorenyl, 2-fluorenyl, 3-fluorenyl, 4-fluorenyl, 1-carbazolyl, 2-carbazolyl, 3-carbazoly and 4-carbazolyl are unsubstituted or substituted by 1 or 2 different or identical substituents selected from Ci-C ₂ -alkyl and Ci-C2-alkoxy, in addition, R ^29a and R ^29b in formulae AR-XCIV and AR-XCV together may form an alkylene group (CH ₂ ) _r with r being 4, 5 or 6.

In a specific embodiment of the compounds of the formula (I) both R ^A groups are a group of the formula AR-LXII, or both R ^A groups are a group of the formula AR-LXIII, or both R ^A groups are a group of the formula AR-LXIV, or both R ^A groups are a group of the formula AR-LXVI, or both R ^A groups are a group of the formula AR-LXVII, or both R ^A groups are a group of the formula AR-LXVIII, or both R ^A groups are a group of the formula AR-LXXXVIII, or both R ^A groups are a group of the formula AR-XCIV or both R ^A groups are a group of the formula AR-XLVIL

In a further specific embodiment of the compounds of the formula (I) both R ^A groups are a group of the formula AR-LXIV, wherein R ⁵ are all hydrogen, or both R ^A groups are a group of the formula AR-LXVIII, wherein R ⁵ are all hydrogen, or both R ^A groups are a group of the formula AR-LXXXVIII, wherein R ²³ , R ²⁵ and R ²⁶ are hydrogen and R ^e and R ^f are methyl, or both R ^A groups are a group of the formula AR-XCIV, wherein R ²¹ , R ²³ , R ²⁴ , R ²⁵ , R ²⁶ , R ²⁷ and R ²⁸ are hydrogen and R ^29a and R ^29b are methyl, both R ^A groups are a group of the formula AR-XLVII, wherein y2 is 0.

In a specific embodiment, the compounds of the formula (I) are selected from the compounds specified in the examples.

The compounds of the invention of the formula (I) and the starting materials used to prepare them can be prepared in analogy to known processes of organic chemistry as described in literature. The substituents, variables and indices are as defined above for formula (I), if not otherwise specified.

Route 1 :

Variant 1 (synthesis of compound (VI) via substeps a11 ) and b11 )

Compounds of the formula wherein X is Cl, Br, I, CH3S R ^1b are as defined above can be prepared by a person skilled in the art by routine procedures. E.g. 2-bromo-9,9-di methylfluorene (CAS No. 28320-31-2) and 2- bromofluorene (CAS No. 113380-8) are commercially available, e.g. from Sigma- Aldrich/Merck.

In step b11 ) the compound (II. a11 ) is reacted with a primary aromatic amine of the formula (111. b11 ) in the presence of a palladium catalyst in terms of a Buchwald- Hartwig reaction. Primary aromatic amines of the formula (lll.bl 1 ) are readily available, e.g. via nitration of an aryl or heteroaryl compound followed by reduction of the obtained nitro compound.

Suitable palladium catalyst or catalyst precursors are for example palladium(O) bis(dibenzylideneacetone) (Pd(dba)2), tris-(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), [1 ,1-bis(diphenylphosphino)-ferrocene]dichloropalladium(ll) (PdCl2(dppf)), palladium chloride (PdCh), bis(acetonitrile)palladium chloride (Pd(ACN)2C ), [1 ,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyr idyl)palladium dichloride (PEPPSI-iPr), dichloro[1 ,3-bis(2,6-di-3-pentylphenyl)imidazol-2-ylidene](3-chloro- pyridyl)palladium (PEPPSI-iPent), or palladium acetate (Pd(OAc)2). Preferably, the catalyst is palladium acetate, Pd(dba)2 or Pd2(dba)3.

The reaction is usually carried out in the presence of a ligand. The ligand is any molecule capable of coordinating to the palladium precursor and facilitating the Buchwald-Hartwig reaction, preferably an dialkylbiarylphosphines or tri-tert-butyl phosphine. Examples of dialkylbiarylphosphine ligands include 2- dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl (DavePhos), 2- dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (Xphos), 2-dicyclohexylphosphino- 2',6'-dimethoxybiphenyl (Sphos), 2-di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl (tBuXPhos), (2-biphenyl)dicyclohexylphosphine, 2-(dicyclohexylphosphino)biphenyl (CyJohnPhos), (2-biphenyl)di-tert-butylphosphine (JohnPhos), 2-dicyclohexyl- phosphino-2',6'-diisopropoxybiphenyl (RuPhos), 2-di-tert-butylphosphino- 2'-methylbiphenyl (tBuMePhos), 2-di-tert-butylphosphino-3,4,5,6-tetramethyl-2',4',6'- tri iso p ropy I- 1 , 1 '-biphenyl 2-di-tert-butylphosphino-2'-methylbiphenyl (tBuMePhos), 2-di-tert-butylphosphino-3,4,5,6-tetramethyl-2',4',6'-triiso propyl-1 , 1 '-biphenyl (Tetramethyl tBuXPhos), and 2-(dicyclophexylphosphino)3,6-dimethoxy-2',4',6'- triisopropyl-1 , 1 '-biphenyl (BrettPhos) or Amphos. The palladium catalyst and phosphine ligand are preferably used in a molar ratio in the range of from about 0.5 to about 5 moles of ligand per mole of palladium catalyst.

Usually, the reaction is performed in the presence of a base such as an alkali alkoxide, earth alkali alkoxide, alkali carbonate or earth alkali carbonate, alkali metal amide or trialkyl amine. Preferably, the base is sodium tert-butoxide, cesium carbonate, lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amide, potassium bis(trimethylsilyl)amide, lithium diisopropylamide or lithium dicyclohexylamide. More preferably, the base is sodium tert-butoxide.

The reaction is generally carried out in a solvent. Suitable solvents are for example aliphatic hydrocarbons, such as pentane, hexane, cyclohexane and petroleum ether, aromatic hydrocarbons, such as toluene, o-, m- and p-xylene, ethers, such as diisopropyl ether, tert-butyl methyl ether, dioxane, anisole and tetrahydrofuran and dimethoxyethane, amides such as dimethylformamide or N-methylpyrrolidone. The reaction temperature generally ranges between 50° and 130°C. The reactions generally are run under an inert atmosphere (e.g. under dry nitrogen or argon). Variant 2 (synthesis of compound (VI) via substeps a12) and b12) Primary aromatic amines of the formula (IV.a12) wherein R ^1a and R ^1b are defined as above and in the following can be obtained by routine methods or are commercially available. 2-Amino-9,9-dimethylfluorene can be purchased e.g. from Alfa Aesar. In step b12), compounds (IV.a12) are subjected to an arylation reaction with an aromatic compound R ^A -X (V.b12). The reaction conditions are analogous to the conditions of the Buchwald-Hartwig reaction of step b11 ).

Step b)

In reaction step b), two reaction equivalents of compound (VI) are reacted with a benzidine derivative of the formula (VII)

Compounds of the formula (VII) and methods for their preparation are known to a person skilled in the art.

Route 2:

A benzidine derivative of the formula (VII) is provided in step a2) and reacted with a primary aromatic amine of the formula (VIII) in step b2). Again, the reaction conditions are analogous to the conditions of the Buchwald-Hartwig reaction of step b11). Intermediate (IX) is subjected to a further Buchwald-Hartwig reaction in step c2) with two equivalents of fluorene derivative (ll.al 1).

Route 3:

In an alternative embodiment, a compound of the formula (X) bearing two secondary amino groups can be provided and reacted with two equivalents of compound of the formula (V.b12) R ^A -X in a Buchwald-Hartwig reaction.

Thus, e.g. JP 2009043896 A and JP 2009158535 A describe a compound (D) and a synthesis starting from 2-iodo-9,9-dimethylfluorene. Goldberg reaction with acetamide leads to 2-(N-acetyl)-9,9-dimethylfluorene that can be coupled by further Goldberg reaction with 4,4'-diiodo-1 ,1 '-biphenyl, followed by saponification of the resulting bis(N-acetyl) derivative.

The compounds according to the invention are in particular suitable for use in an electronic device. An electronic device here is taken to mean a device which comprises at least one layer which comprises at least one organic compound.

The present invention therefore furthermore relates to the use of the compounds of formula (I) or a mixture of at least two different compounds thereof as a hole transport material (HTM) in organic electronics, as an electron blocking material (EBM) in organic electronics, in organic solar cells (OSCs), solid-state dye sensitized solar cells (DSSCs) or Perovskite solar cells, in particular as a hole transport material in organic solar cells, as replacement of the liquid electrolyte in dye sensitized solar cells, as a hole transport material in Perovskite solar cells, in organic light-emitting diodes (OLEDs), in particular for displays on electronic devices and lighting, for electrophotography, in particular as photoconductive material in an organic photoconductor (OPC), for organic optical detectors, organic photoreceptors, organic field-quench devices (O-FQDs), light-emitting electrochemical cells (LECs) and organic laser diodes. The compounds according to the invention are especially suitable as a hole transport material (HTM) in organic electronics. HTMs are employed in a wide range of electronic devices and applications, such as in organic electroluminescent (EL) devices and in solar cells.

The compounds according to the invention may be employed as the sole HTM or in combination with at least one further HTM. Suitable further hole transport materials are well-known in the art. Preferred hole transport materials for combination are spiro- OMeTAD, 2,2',7,7'-tetrakis-(N,N'-di-4-methoxy-3,5-dimethylphenylamme )-9,9'- spirofluorene, tris(p-anisyl)amine, N,N,N',N'-tetrakis(4-methoxyphenyl)-1 ,T-biphenyl- 4,4'-diamine, 2,7-bis[N,N-bis(4-methoxy-phenyl)amino]-9,9-spirobifluorene, poly(3- hexylthiophene) (P3HT), poly(3,4-ethylenedioxythiophene)-poly( styrenesulfonate) (PEDOT:PSS), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA).

Typical hole transport materials for perwoskite solar cells have been the subject of reviews, e.g. Z. Shariatinia, “Recent progress in development of diverse kinds of hole transport materials for the perovskite solar cells: A review”, Renewable and Sustainable Energy Reviews, 2020, 119,109608, D0l:10.1016/j.rser.2019.109608.

Furthermore, the compounds according to the invention used as HTMs may be combined with at least one further additive. Suitable additives are pyridine compounds such as tert-butylpyridine, imidazoles as disclosed in WO2013/026563, claims 1 to 15 and disclosed on pages 15 to 17 or polymer additives such as poly(4-vinylpyridine) or its copolymer with e.g. vinylstyrene or alkylmethacrylate. A preferred pyridine compound is tert-butylpyridine.

The compounds according to the invention used as the HTMs may be combined with lithium salts as described in Phys. Chem., Chem. Phys, 2013, 15, 1572-2579.

The usefulness of a pyridine compound is described in Sol. Energy Mater. & Solar Cells, 2007, 91 , 424-426.

Furthermore, the compounds according to the invention used as HTMs may be combined with a p-dopant such as N(C ₆ H5Br) ₃ , SbCh, V2O5, M0O3, WO3, Re ₂ O3, F ₄ - TCNQ (tetrafluoro-tetracyanoquinodimethane), HAT-CN (1 ,4, 5, 8, 9,11 -hexaazatri- phenylene-hexacarbonitrile) F6-TCNNQ (1 ,3,4,5,7,8-hexafluorotetracyanonaphtho- quinodimethane, obtainable from Novaled), NDP-9 (a p-dopant obtainable from Novaled) or Co complex salts. Suitable dopants are described in Chem. Mater., 2013, 25, 2986-2990 or J. Am. Chem. Soc, 2011 , 133, 18042. Also suitable [3]-radialenes as described in EP 2 180 029 A1 can be applied. Suitable are also the cerium (IV) complexes described in WO 2021/048044 A1 and the Cerium-ethylenediamine ketone- type and Cerium-salene-type complexes described in WO 2022101343 A1.

The invention furthermore relates to an electroluminescent arrangement comprising an upper electrode, a lower electrode, wherein at least one of said electrodes is transparent, an electroluminescent layer and optionally an auxiliary layer, wherein the electroluminescent arrangement comprises at least one compound of the formula (I). The preferences stated above likewise apply to the substrate. Especially, the at least one compound of the formula (I) or (I. a) is employed in a hole-transporting layer or electron blocking layer.

The invention furthermore relates to an electroluminescent arrangement in form of an organic light-emitting diode (OLED). In an organic light emitting device, an electron blocking layer is disposed adjacent to an emissive layer. Blocking layers may be used to reduce the number of charge carriers (electrons or holes) and/or excitons that leave the emissive layer. An electron blocking layer may be disposed between emissive layer and an hole transport layer, to block electrons from leaving emissive layer in the direction of hole transport layer. Similarly, a hole blocking layer may be disposed between emissive layer and electron transport layer, to block holes from leaving emissive layer in the direction of electron transport layer.

The OLEDs can be employed for various applications, for example for monochromatic or polychromatic displays, for lighting applications or for medical and/or cosmetic applications, for example in phototherapy.

The organic electroluminescent device, particularly in form of an OLED, comprises a cathode, an anode and at least one emitting layer. Apart from these layers, it may also comprise further layers, for example in each case one or more holeinjection layers, hole-transport layers, hole-blocking layers, electron-transport layers, electron-injection layers, exciton-blocking layers, electron-blocking layers and/or charge-generation layers. Interlayers, which have, for example, an exciton-blocking function, may likewise be introduced between two emitting layers. However, it should be noted that each of these layers does not necessarily have to be present.

The organic electroluminescent device here may comprise one emitting layer or a plurality of emitting layers. If a plurality of emission layers is present, these preferably have in total a plurality of emission maxima between 380 nm and 750 nm, resulting overall in white emission, i.e. various emitting compounds which are able to fluoresce or phosphoresce are used in the emitting layers. Particular preference is given to systems having three emitting layers, where the three layers exhibit blue, green and orange or red emission (for the basic structure see, for example, WO 2005/011013). It is possible here for all emitting layers to be fluorescent or for all emitting layers to be phosphorescent or for one or more emitting layers to be fluorescent and one or more other layers to be phosphorescent.

The compound according to the invention in accordance with the embodiments indicated above can be employed here in different layers, depending on the precise structure. Preference is given to an organic electroluminescent device comprising a compound of the formula (I) or the preferred embodiments as hole-transport material in a hole-transport or hole-injection or electron-blocking layer or as matrix material for fluorescent or phosphorescent emitters, in particular for phosphorescent emitters. The preferred embodiments indicated above also apply to the use of the materials in organic electronic devices.

In a preferred embodiment of the invention, the compound of the formula (I) or the preferred embodiments is employed as hole-transport or hole-injection material in a hole-transport or hole-injection layer. The emitting layer here can be fluorescent or phosphorescent.

A hole-injection layer generally is a layer which facilitates electron injection from the anode to the organic layer. The hole-injection layer can be situated directly adjacent to the anode.

A hole-transport layer transports the holes from the anode to the emitting layer and is located between a hole-injection layer and an emitting layer. To enhance the hole transport characteristics, doped hole transport layers can be employed. The architecture of actual OLEDs often improves quantum efficiency by using a graded heterojunction. In the graded heterojunction architecture, the composition of hole and electron-transport materials varies continuously within the emissive layer with a dopant emitter. The graded heterojunction architecture combines the benefits of both conventional architectures by improving charge injection while simultaneously balancing charge transport within the emissive region.

In still a further preferred embodiment of the invention, the compounds of the formula (I) or the preferred embodiments thereof are employed in an electron-blocking layer. An electron-blocking layer may be used to reduce the number of charge carriers (electrons) that leave the emissive layer. An electron-blocking layer usually is a layer which is directly adjacent to an emitting layer on the anode side. An electron blocking layer may be disposed between emissive layer and hole transport layer to block electrons from leaving the emissive layer in the direction of hole transport layer.

The compound of the formula (I) or the preferred embodiments thereof are particularly preferably employed in a hole-transport layer or electron blocking layer.

In a further preferred embodiment of the invention, the compound of the formula (I) or the preferred embodiments thereof are employed as matrix material for a fluorescent or phosphorescent compound, in particular for a phosphorescent compound, in an emitting layer. The organic electroluminescent device here may comprise one emitting layer or a plurality of emitting layers, where at least one emitting layer comprises at least one compound according to the invention as matrix material.

If the compound of the formula (I) or the preferred embodiments thereof are employed as matrix material for an emitting compound in an emitting layer, it is preferably employed in combination with one or more phosphorescent materials (triplet emitters). Phosphorescence in the sense of this invention is taken to mean the luminescence from an excited state having a spin multiplicity >1 , in particular from an excited triplet state. For the purposes of this application, all luminescent complexes containing transition metals or lanthanoids, in particular all luminescent iridium, platinum and copper complexes, are to be regarded as phosphorescent compounds.

The mixture comprising the compound of the formula (I) or the preferred embodiments and the emitting compound comprises between 99.9 and 1% by weight, preferably between 99 and 10% by weight, particularly preferably between 97 and 60% by weight, in particular between 95 and 80% by weight, of the compound of the formula (I) or the preferred embodiments, based on the entire mixture comprising emitter and the compound of the formula (I). Correspondingly, the mixture comprises between 0.1 and 99% by weight, preferably between 1 and 90% by weight, particularly preferably between 3 and 40% by weight, in particular between 5 and 20% by weight, of the emitter, based on the entire mixture comprising emitter and the compound of the formula (I).

A further object of the invention is the use of at least one compound of the general formula (I) as defined above in organic solar cells (OSCs). The compounds of the general formula (I) are used in particular as a hole transport material or electron blocking material in organic solar cells. Organic solar cells generally have a layer structure and generally comprise at least the following layers: anode, photoactive layer and cathode. These layers are generally applied to a substrate suitable for this purpose. The structure of organic solar cells is described, for example, in US 2005/0098726 and US 2005/0224905.

The invention provides an organic solar cell which comprises a substrate with at least one cathode and at least one anode, and at least one compound of the general formula (I) as defined above as a material of at least one of the layers. The organic solar cell of the invention comprises at least one photoactive region. A photoactive region may comprise two layers, each of which has a homogeneous composition and forms a flat donor-acceptor heterojunction. A photoactive region may also comprise a mixed layer and form a donor-acceptor heterojunction in the form of a donor-acceptor bulk heterojunction

Consequently, the invention also refers to an organic solar cell, comprising: a cathode, an anode, one or more photoactive regions comprising at least one donor material and at least one acceptor material in separate layers or in form of a bulk heterojunction layer, optionally at least one further layer selected from exciton blocking layers, electron conducting layers, hole transport layers, wherein the organic solar cell comprises at least one compound of the formula (I) as defined above or of a composition comprising at least two different compounds of the general formula (I) as defined above.

In a first embodiment, the heterojunction can have a flat configuration (see: Two layer organic photovoltaic cell, C. W. Tang, Appl. Phys. Lett., 48 (2), 183-185 (1986) or N. Karl, A. Bauer, J. Holzapfel, J. Marktanner, M. Mbbus, F. Stolzle, Mol. Cryst. Liq. Cryst., 252, 243-258 (1994).).

In a second embodiment, the heterojunction can be a bulk heterojunction, also referred to as an interpenetrating donor-acceptor network. Organic photovoltaic cells with a bulk heterojunction are described, for example, by C. J. Brabec, N. S. Sariciftci, J. C. Hummelen in Adv. Funct. Mater., 11 (1), 15 (2001 ) or by J. Xue, B. P. Rand, S. Uchida and S. R. Forrest in J. Appl. Phys. 98, 124903 (2005).

The compounds of the general formula (I) can be used in cells with MiM, pin, pn, Mip or Min structure (M = metal, p = p-doped organic or inorganic semiconductor, n = n-doped organic or inorganic semiconductor, i = intrinsically conductive system of organic layers; see, for example, J. Drechsel et al., Org. Electron., 5 (4), 175 (2004) or Maennig et al., Appl. Phys. A 79, 1-14 (2004)).

The compounds of the formula (I) can also be used in tandem or triple stack cells. Tandem cells are described, for example, by P. Peumans, A. Yakimov, S. R. Forrest in J. Appl. Phys, 93 (7), 3693-3723 (2003). A tandem cell consists of two or more than two subcells. A single subcell, some of the subcells or all subcells may have photoactive donor-acceptor heterojunctions. Each donor-acceptor-heterojunction may be in the form of a flat heterojunction or in the form of a bulk heterojunction. The subcells which form the tandem cell may be connected in parallel or in series. There is preferably an additional recombination layer in each case between the individual subcells. The individual subcells have the same polarity, i.e. generally either only cells with normal structure or only cells with inverse structure are combined with one another.

Suitable substrates for organic solar cells are, for example, oxidic materials, polymers and combinations thereof. Preferred oxidic materials are selected from glass, ceramic, SiO?, quartz, etc. Preferred polymers are selected from polyethylene terephthalates, polyolefins (such as polyethylene and polypropylene), polyesters, fluoropolymers, polyamides, polyurethanes, polyalkyl (meth)acrylates, polystyrenes, polyvinyl chlorides and mixtures and composites.

Suitable electrodes (cathode, anode) are in principle semiconductors, metal alloys, semiconductor alloys and combinations thereof. Preferred metals are those of groups 2, 8, 9, 10, 11 or 13 of the periodic table, e.g. Pt, Au, Ag, Cu, Al, In, Mg or Ca. Preferred semiconductors are, for example, doped Si, doped Ge, indium tin oxide (ITO), fluorinated tin oxide (FTO), gallium indium tin oxide (GITO), zinc indium tin oxide (ZITO), etc. Preferred metal alloys are for example alloys based on Pt, Au, Ag, Cu, etc.

The material used for the electrode facing the light (the anode in a normal structure, the cathode in an inverse structure) is preferably a material at least partly transparent to the incident light. This preferably includes electrodes which have glass and/or a transparent polymer as a carrier material. The electrical contact connection is generally effected by means of metal layers and/or transparent conductive oxides (TCOs). These preferably include ITO, doped ITO, FTO (fluorine doped tin oxide), AZO (aluminum doped tin oxide), ZnO, TiOa, Ag, Au, Pt. In a specific embodiment, the material used for the electrode facing away from the light (the cathode in a normal structure, the anode in an inverse structure) is a material which at least partly reflects the incident light. This includes metal films, preferably of Ag, Au, Al, Ca, Mg, In, and mixtures thereof.

In a first embodiment, the organic solar cells according to the invention are present as an individual cell with flat heterojunction and normal structure. In a specific embodiment, the cell has the following structure: an at least partly transparent conductive layer (top electrode, anode) a hole-conducting layer (hole transport layer, HTL) a layer which comprises a donor material a layer which comprises an acceptor material an exciton-blocking and/or electron-conducting layer a second conductive layer (back electrode, cathode)

In a second embodiment, the organic solar cells according to the invention are present as an individual cell with a flat heterojunction and inverse structure. In a specific embodiment, the cell has the following structure: an at least partly transparent conductive layer (cathode) an exciton-blocking and/or electron-conducting layer a layer which comprises an acceptor material a layer which comprises a donor material a hole-conducting layer (hole transport layer, HTL) a second conductive layer (back electrode, anode) In a third embodiment, the organic solar cells according to the invention are present as an individual cell with normal structure and have a bulk heterojunction. In a specific embodiment, the cell has the following structure: an at least partly transparent conductive layer (anode) a hole-conducting layer (hole transport layer, HTL) a mixed layer which comprises a donor material and an acceptor material, which form a donor-acceptor heterojunction in the form of a bulk heterojunction an electron-conducting layer an exciton-blocking and/or electron-conducting layer a second conductive layer (back electrode, cathode)

In a fourth embodiment, the organic solar cells according are present as an individual cell with inverse structure and have a bulk heterojunction.

Examples of different kinds of donor-acceptor heterojunctions are a donoracceptor double layer with a flat heterojunction, or the heterojunction is configured as a hybrid planar-mixed heterojunction or gradient bulk heterojunction or annealed bulk heterojunction. The production of a hybrid planar-mixed heterojunction is described in Adv. Mater. 17, 66-70 (2005). In this structure, mixed heterojunction layers which were formed by simultaneous evaporation of acceptor and donor material are present between homogeneous donor and acceptor material. In a further specific embodiment, the donor-acceptor-heterojunction is in the form of a gradient bulk heterojunction. In the mixed layers composed of donor and acceptor materials, the donor-acceptor ratio changes gradually. In a further specific embodiment, the donor-acceptor-heterojunction is configured as an annealed bulk heterojunction; see, for example, Nature 425, 158- 162, 2003. The process for producing such a solar cell comprises an annealing step before or after the metal deposition. As a result of the annealing, donor and acceptor materials can separate, which leads to more extended percolation paths.

A further object of the invention is the use of at least one compound of the general formula (I) or (LA) as defined above in solid-state dye sensitized solar cells (DSSCs) or Perovskite solar cells. These compounds are used in particular as replacement of the liquid electrolyte in dye sensitized solar cells and as a hole transport material in Perovskite solar cells.

The compounds of the formula (I) or (LA) can be used advantageously as HTMs in perovskite solar cells. They can also be used to replace the liquid electrolyte of conventional DSSCs to provide solid-state DSSC devices.

The compounds of the invention are then preferably employed in a photosensitized nanoparticle layer comprising a sensitizing dye or a perovskite and at least one compound of the general formula (I) according to the invention.

In a first embodiment, the compounds of the invention are employed in a DSSC. The construction of a DSSC is generally based on a transparent substrate, which is coated with a transparent conductive layer, the working electrode. An n-conductive metal oxide is generally applied to this electrode or in the vicinity thereof, for example a nanoporous TiO2 layer of approximately 2 to 20 pm thickness. On the surface thereof, in turn, a monolayer of a light-sensitive dye is typically adsorbed, which can be converted to an excited state by light absorption. This layer which carries the lightsensitive dye is generally referred to as the light absorbing layer of the DSSC. The counter electrode may optionally have a catalytic layer of a metal, for example platinum, with a thickness of a few pm.

Suitable are in principle all sensitizing dyes, as long as the LUMO energy state is marginally above the conduction bandedge of the photoelectrode to be sensitized. Examples of dyes are disclosed in Nanoenergy, de Souza, Flavio Leandro, Leite, Edson Roberto (Eds.), Springer, ISBN 978-3-642-31736-1 , pages 58 to 74 or black dyes as described in US 8,383,553. Preferred dyes are described in WO 2015049031 A1 which is incorporated herein by reference.

In a second embodiment, the compounds of the invention are employed in a Perovskite solar cell. Suitable Perovskites for Perovskite solar cells (PSCs) are known in the art. In principle, the perovskite material comprised in the devices according to the invention may be part of the charge transport layer but may also be part of another layer or scaffold within the device.

Suitable perovskite materials may comprise two halides corresponding to formula Xa _p.x Xb(x), wherein Xa and Xb are each independently selected from Cl, Br, or I, and x is greater than 0 and less than 3. Suitable pervoskite materials are also disclosed in WO 2013/171517, claims 52 to 71 and claims 72 to 79, which is entirely incorporated herein by reference. Suitable pervoskite materials are CsSnl ₃ , CH ₃ NH ₃ Pbl2CI, CH ₃ NH ₃ Pbl ₃ , CH ₃ NH ₃ Pb(li- _x Br _x ) ₃ , CH ₃ NH ₃ Snl ₂ CI, CH ₃ NH ₃ Snl ₃ or CH ₃ NH ₃ Sn(li- _x Br _x ) ₃ , with 0<x<1.

Preferred perovskite materials are disclosed in WO 2013/171517 on page 18, lines 5 to 17. As described, the perovskite is usually selected from CH ₃ NH ₃ PbBrl ₂ , CH ₃ NH ₃ PbBrCI ₂ , CH ₃ NH ₃ PblBr ₂ , CH ₃ NH ₃ PblCI ₂ , CH ₃ NH ₃ SnF ₂ Br, CH ₃ NH ₃ SnF ₂ l and (H ₂ N=CH-NH ₂ )Pbl _3z Br ₃ (i-z), wherein z is greater than 0 and less than 1 .

The charge transport layer according to the invention as described before or the device according to the invention as described before or below may furthermore comprise an insulator such as alumina as described in Michael M. Lee et al, Science, 338, 643, 2012.

The charge transport layer according to the invention or the device according to the invention as described before or below may furthermore comprise semiconductor oxide nanoparticles. The charge transport layer according to the invention or the device according to the invention preferably comprises semiconductor oxide nanoparticles.

According to a preferred embodiment of the invention, the semiconductor is based on material selected from the group of Si, TiO ₂ , SnO ₂ , Fe ₂ O ₃ , WO ₃ , ZnO, Nb ₂ O ₅ , CdS, ZnS, PbS, Bi ₂ S ₃ , CdSe, GaP, InP, GaAs, CdTe, CulnS ₂ , and/or CulnSe ₂ .

Preferably, the charge transport layer according to the invention as described before is present on a glass support or plastic or metal foil, optionally together with a dense layer of TiO ₂ . Preferably, the support is conductive.

The present invention furthermore relates to a electronic device or optoelectronic device comprising a charge transport layer as described or preferably described before. Preferably, the invention relates furthermore to a solid-state dye-sensitized solar cell comprising a charge transport layer as described or preferably described before. Suitable device structures according to the invention comprising further a mixed halide perovskite are described in WO 2013/171517, claims 52 to 71 and claims 72 to 79, which is entirely incorporated herein by reference. Suitable device structures according to the invention comprising further a dielectric scaffold together with perovskite material are described in WO 2013/171518, claims 1 to 90 or WO 2013/171520, claims 1 to 94 which are entirely incorporated herein by reference.

Suitable device structures according to the invention comprising further a semiconductor and a perovskite material are described in WO 2014/020499, claims 1 and 3 to 14, which is entirely incorporated herein by reference The surface-increasing scaffold structure described therein comprises nanoparticles which are applied and/or fixed on a support layer, e.g. porous IO ₂ .

Suitable device structures according to the invention comprising a planar heterojunction are described in WO 2014/045021 , claims 1 to 39, which is entirely incorporated herein by reference. Such a device is characterized in having a thin film of a light-absorbing or light-emitting perovskite disposed between n-type (electron conducting) and p-type (hole-conducting) layers. Preferably, the thin film is a compact thin film. Additionally, the invention relates to a method of preparing an electrochemical device and/or optoelectronic device as described or preferably described before, the method comprising the steps of:

- providing a first and a second electrode;

- providing a charge transport layer according to the invention as described before. There are no restrictions per se with respect to the choice of the first and second electrode. The substrate may be rigid or flexible.

Abbreviations which have been used in the examples that follow are: Al for aluminium;

DCM for dichloromethane;

HPLC for high-performance liquid chromatography;

HSQC for heteronuclear single quantum coherence ITO for indium tin oxide;

NDP-9, NHT-18, Novaled n-dopant, can be purchased from Novaled AG, Germany; NMR for nuclear magnetic resonance;

Pd(dba) ₂ for palladium(O) bis(dibenzylideneacetone);

Pd ₂ (dba)s for tris(dibenzylideneacetone)dipalladium(0);

RuPhos for 2-dicyclohexylphosphino-2',6'-diisopropoxybiphenyl;

SPhos for 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl;

TBME for tert-butyl methyl ether;

THF for tetrahydrofuran; v/v for volume/volume.

Further definitions: Room temperature means a temperature range of from ca. 20 to 25 °C. Over night means a time period in the range of from 14 to 20 h.

EXAMPLES

General procedure A for Buchwald-Hartwig amination: Under an inert atmosphere, the aryl halide, the mono- or di-arylamine and sodium tertbutanolate are suspended in toluene (ca. 15 mL I mmol aryl halide). To the obtained suspension is added under an inert atmosphere the catalyst made up from Pd2(dba)s and the appropriate ligand (P(t-Bu3)*HBF4 or Amphos (di-tert -butyl-(4- dimethylaminophenyl)-phosphine)). The resulting mixture is heated at reflux for 16 hours.

Workup procedures for Buchwald-Hartwig aminations:

Workup procedure A:

After cooling, aqueous ammonium chloride solution (ca. 20%, 10 ml / mmol product) is added to the reaction mixture. The resulting emulsion is filtered through a filter layer (d = 6 cm, h = 3 cm) which was made up of Celite, which had been slurried in ethyl acetate. Later, the Celite pad is washed with ethyl acetate (ca. 15 mL / mmol) to rinse down the product. From the filtrates, the organic layer is separated and washed first with water (10 mL / mmol), and then with saturated sodium chloride solution (10 mL / mmol). Then, the organic layer is dried with anhydrous sodium sulfate. Filtration and removal of the solvent from the filtrate gives the crude product. This is purified further as described for the corresponding examples.

Workup procedure B:

After cooling, aqueous ascorbic acid solution (5 %, ca. 10 ml / mmol) is added to the reaction mixture. The resulting emulsion is filtered through a Celite pad (d = 6 cm, h = 3 cm) which has been made up as described in Workup A, and subsequently washed with ethyl acetate (ca. 15 mL / mmol). From the filtrate, the organic layer is separated and washed first with water (10 mL / mmol), and then with saturated sodium chloride solution (10 mL / mmol). Then the organic layer is dried with anhydrous sodium sulfate. Filtration and removal of the solvent from the filtrate gives the crude product. This is purified further as described for the corresponding examples.

Workup procedure C:

After cooling, silica gel (ca. 2 g / mmol) is added to the reaction mixture. The suspension is stirred until it appears to be homogenous. It is then filtered over a pad of silica gel (20- 30 g), which is then washed with about the same volume of toluene as the volume of the column. After removal of the solvent from the combined filtrates, the product is purified further as described for the corresponding examples.

Workup procedure D:

After cooling, functionalized silica gel (1.5 g, 3-Mercaptopropyl ethyl sulfide silica, SPM32, PhosphonicS.com) is added to the reaction mixture. The suspension is stirred until it appears to be homogenous. It is then filtered over a pad of silica gel (20-30 g), which is then washed with about the same volume of toluene as the volume of the column. After removal of the solvent from the combined filtrates, the product is purified further as described for the corresponding examples. I) Preparation of Intermediates

I. a) Preparation of Aryl bromide precursors

Example 1 :

4,4'-dibromo-2,2'-dimethyl-1 , 1 '-biphenyl

This compound was prepared as described in JP2011140579A from 5-bromo-2- iodotoluene (38.0 g, 128 mmol, 1 .0 eq.) via transformation into the corresponding boromc acid (4-bromo-2-methylphenyl)boronic acid followed by Suzuki coupling of this acid with 5-bromo-2-iodotoluene. The crude product was purified by distillation in vacuum followed by crystallization from ethanol to give the product as a colorless solid (15.9 g, 40%) in a purity of 99.3% (according to GC).

¹³ C-NMR (101 MHz, CDCh): 5 139.26 (2 x C-q), 138.11 (2 x C-q), 132.78 (2 x CH), 130.73 (2 x CH), 128.81 (2 x CH), 121 .31 (2 x C-q), 19.66 (2 x CH ₃ ).

Lb) Preparation of secondary amine precursors

Example 2

N-(9,9-dimethyl-9H-fluoren-2-yl)dibenzo[b,d]furan-2-amine

This material was synthesized as described in WO 2018/206769 A1 via the coupling of 2-bromo-dibenzo[b,d]furan with 9,9-dimethyl-9H-fluoren-2-amine.

¹³ C / ¹ H-NMR (101 MHz, 400 MHz (HSQC), CS ₂ : acetone-d ₆ 5:1): 8 / § (27.22 / 1.49, 2 x CH ₃ ), (46.44, C-q), (110.34 / 7.76, CH), (110.87 / 7.17, CH), (111.73 / 7.52, CH),

(112.13 / 7.46, CH), (115.48 / 7.05, CH), (118.97 / 7.56, CH), (119.97 / 7.28, CH),

(120.84 / 7.90, CH), (120.98 / 7.54, CH), (122.45 / 7.36, CH), (122.68 / 7.31 , CH),

(124.46, C-q), (124.96, C-q), (125.91 / 7.17, CH), (127.12 / 7.24, CH), (127.23 / 7.44,

CH), (131.37, C-q), (139.23, C-q), (139.69, C-q), (144.64, C-q), (151.50, C-q), (152.73, C-q), (155.07, C-q), (156.75, C-q), (7.13, NH).

Example 3

N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9-dimethyl-9H-xanthen- 2-amine

This material was synthesized as described in WO 2021/141356 A1 via the coupling of 9,9-dimethyl-9H-fluoren-2-amine with 2-bromo-9,9-dimethyl-9H-xanthene, using Amphos instead of P(f-Bu) ₃ as ligand.

¹³ C / ¹ H-NMR (101 MHz, 400 MHz (HSQC), CS ₂ : acetone-d ₆ 5:1 ): 8 / 8 (27.36 / 1.50, 2 x CH ₃ ), (32.59 / 1 .69, 2 x CH ₃ ), (34.06, C-q), (46.46, C-q), (110.48 / 7.07, CH), (115.65 / 6.91 , CH), (116.54 / 7.00, CH), (117.05 / 7.23, CH), (117.28 / 6.97, CH), (119.07 / 7.55, CH), (119.19 / 6.97, CH), (121.15 / 7.52, CH), (122.53 / 7.35, CH), (123.17 / 7.07, CH), (126.06 / 7.20, CH), (126.42 / 7.41 , CH), (127.24 / 7.26, CH), (127.60 / 7.19, CH), (129.22, C-q), (130.33, C-q), (131.38, C-q), (138.43, C-q), (139.62, C-q), (144.30, C-q), (145.05, C-q), (150.44, C-q), (152.68, C-q), (155.06, C-q), (6.17, NH).

Example 4

N-(9,9-dimethyl-9H-fluoren-2-yl)-3,3-dimethyl-2,3-dihydro benzofuran-5-amine

This material was synthesized via the coupling of 9,9-dimethyl-9H-fluoren-2-amine with 5-bromo-3,3-dimethyl-2,3-dihydro-benzofuran

¹³ C / ¹ H-NMR (101 MHz / 400 MHz (HSQC), CS ₂ : acetone-d ₆ 5:1 ): 8 / 6 (27.31 / 1.44, 2 x CH ₃ ), (27.41 / 1.37, 2 x CH ₃ ), (41.97, C-q), (46.32, C-q), (84.40 / 4.20, CH ₂ ), (109.60 / 6.95, CH), (110.04 / 6.62, CH), (114.53 / 6.81 , CH), (115.59 / 6.93, CH), (118.80 / 7.48, CH), (120.74 / 6.87, CH), (120.95 / 7.43, CH), (122.38 / 7.31 , CH), (125.67 / 7.13, CH), (127.09 / 7.21 , CH), (130.43, C-q), (136.26, C-q), (137.18, C-q), (139.83, C-q), (145.63, C-q), (152.54, C-q), (154.77, C-q), (154.94, C-q), (6.46, NH).

Example 5

N-(9,9-dimethyl-9H-fluoren-2-yl)dibenzo[b,d]thiophen-2-am ine

The amine was synthesized as described in KR 2016149879 A via the coupling of 2- bromodibenzo[b,d]thiophene with 9,9-dimethyl-9H-fluoren-2-amine using Amphos instead of P(t-Bu) ₃ as ligand.

¹³ C / ¹ H-NMR (101 MHz / 400 MHz (HSQC), CS ₂ /acetone-d ₆ 5:1): 8 / 8 (27.32 / 1.51 , 2 x CH ₃ ), (46.51 , C-q), (110.11 / 7.92, CH), (111.88 / 7.23, CH), (116.58 / 7.09, CH), (119.18 / 7.56, CH), (119.27 / 7.27, CH), (121 .10 / 7.56, CH), (121 .69 / 8.00, CH), (122.52 / 7.35, CH), (123.01 I 7.79, CH), (123.43 / 7.67, CH), (124.35 / 7.39, CH), (126.19 / 7.19, CH), (126.85 / 7.41 , CH), (127.23 / 7.25, CH), (131.43, C-q), (132.16, C-q), (135.49, C-q), (136.71 , C-q), (139.56, C-q), (140.65, C-q), (141.14, C-q), (143.51 , C-q), (152.79, C-q), (155.08, C-q), (6.97, NH).

Example 6

N ⁴ , N ⁴ '-bis(9,9-dimethyl-9H-fluoren-2-yl)-[1 , 1 '-biphenyl]-4,4'-diamine

As described in general procedure A, the aryl bromide 4,4'-dibromo-1 ,T-biphenyl (27.5 g, 88.1 mmol, 1.0 eq.) and the arylamine 9,9-dimethyl-9H-fluoren-2-amine (37.8 g, 181 mmol, 2.05 eq.) were coupled in toluene (350 mL), using sodium tert-butanolate (17.8 g, 185 mmol, 2.1 eq.), Amphos (0.477 g, 1.76 mmol, 2 mol-%) and Pd ₂ (dba) ₃ (0.404 g, 0.441 mmol, 0.5 mol-%). After two hours at reflux, the reaction was complete.

The product was worked up according to procedure D.

The crude product was purified by crystallization from toluene to give the product as an off white solid (39.6 g, 79%) in a purity of 99.1 % according to HPLC@340 nm. Further purification by a second crystallization from toluene gave the product as an off white solid (31 .8 g, 63%) in a purity 99.8% according to HPLC@340 nm.

¹³ C / ¹ H-NMR (101 MHz / 400 MHz (HSQC), CS ₂ : acetone-d ₆ 5:1 ): 5 / 5 (27.29 / 1.49, 4 x CH ₃ ), (46.46, 2 x C-q), (111.78 / 7.17, 2 x CH), (116.60 / 7.05, 2 x CH), (118.00 / 7.14, 4 x CH), (119.11 / 7.54, 2 x CH), (120.96 / 7.52, 2 x CH), (122.4717.34, 2 x CH), (126.08 / 7.17, 2 x CH), (127.16 I 7.23, 2 x CH), (127.25 / 7.43, 4 x CH), (131.93, 2 x C-q), (133.13, 2 x C-q), (139.59, 2 x C-q), (142.17, 2 x C-q), (143.18, 2 x C-q), (152.76, 2 x C- q), (154.95, 2 x C-q), (6.93, 2 x NH).

II Preparation of hole transport materials

Example 7 (comparative example, not inventive)

N ⁴ ,N ⁴ ,N ⁴ ’,N ⁴ -tetrakis(9,9-dimethyl-9H-fluoren-2-yl)-[1 ,1'-biphenyl]-4,4'-diamine

As described in the general procedure A, the aryl bromide 4, 4'-dibromo-1 ,1 '-biphenyl (3.30 g, 10.6 mmol, 1.0 eq.) and the diarylamine bis(9,9-dimethyl-9H-fluoren-2-yl)amine (8.92 g, 22.2 mmol, 2.1 eq.) were coupled in toluene (120 mL), using sodium tert- butanolate (2.24 g, 23.3 mmol, 2.2 eq.), Amphos (0.058 g, 0.21 mmol, 2 mol-%) and Pd ₂ (dba) ₃ (0.048 g, 0.05 mmol, 0.5 mol-%).

The product was worked up according to procedure B.

Purification of the crude product by crystallization from toluene provided the product as a yellowish solid (7.0 g, 69%) purity 99.6% according to HPLC@340 nm.

5.01 g of the title compound was further purified by vacuum zone sublimation (10 ^-6 - 10" ⁷ mbar, 200-340°C) to give the title compound as a yellowish solid (2.84 g, purity up to 99.8% according to HPLC@340 nm.

¹³ C / ¹ H-NMR (101 MHz, 400 MHz (HSQC), CS ₂ : acetone-d ₆ 5:1): 5 / 5 (27.06 / 1.46, 8 x CH ₃ ), (46.60, 4 x C-q), (118.67 / 7.29, 4 x CH), (119.67 / 7.60, 4 x CH), (120.96 / 7.59, 4 x CH), (122.62 / 7.37, 4 x CH), (123.29 / 7.11 , 4 x CH), (124.50 / 7.23, 2 x CH), (126.79 / 7.22, 4 x CH), (127.29 / 7.27, 4 x CH), (127.57 / 7.50, 2 x CH), (134.33, 4 x C-q), (134.90, 2 x C-q), (139.02, 4 x C-q), (146.81 , 2 x C-q), (147.25, 4 x C-q), (153.23, 4 x C- q), (154.86, 4 x C-q).

Example 8

N ⁴ ,N ⁴ '-bis(9,9-dimethyl-9H-fluoren-2-yl)-N ⁴ ,N ⁴ '-bis(9,9-dimethyl-9H-xanthen-2-yl)-[1 ,T- biphenyl]-4,4'-diamine

As described in the general procedure A, the aryl bromide 4,4'-dibromo-1 ,1 '-biphenyl (3.65 g, 11.7 mmol, 1.0 eq.) and the diarylamine from example 3 (10.3 g, 24.6 mmol, 2.1 eq.) were coupled in toluene (120 mL), using sodium tert-butanolate (2.47 g, 25.7 mmol, 2.2 eq.), Amphos (0.063 g, 0.23 mmol, 2 mol-%) and Pd ₂ (dba) ₃ (0.054 g, 0.06 mmol, 0.5 mol-%).

The product was worked up according to procedure C. The crude product was purified by double crystallization from toluene/acetone to provide the product as a yellowish solid (8.1 g, 70%) in a purity of 97.1% according to HPLC@340 nm.

1.50 g of the title compound was further purified by vacuum zone sublimation (1 O’ ⁶ - 10 ⁷ mbar, 200-340°C) to give the title compound as a yellowish solid (1.25 g, purity up to 98.5% according to HPLC@340 nm).

¹³ C / ¹ H-NMR (101 MHz / 400 MHz (HSQC), CDCI ₃ ): 8 / 8 (27.14, 4 x CH ₃ ), (32.40, 4 x CH ₃ ), (34.25, 2 x C-q), (46.82, 2 x C-q), (116.36 / 7.09, 2 x CH), (117.21 / 7.04, 2 x CH), (117.61 / 7.24, 2 x CH), (119.33 / 7.68, 2 x CH), (120.56 / 7.62, 2 x CH), (122.28 / 7.11 , 2 x CH), (122.48 / 7.42, 2 x CH), (123.03 / 7.30, 2 x CH), (123.05 / 7.11 , 2 x CH), (123.42 / 7.22, 4 x CH), (124.65 / 7.05, 2 x CH), (126.19 / 7.42, 2 x CH), (126.36 / 7.29, 2 x CH), (126.99 / 7.35, 2 x CH), (127.16 / 7.55, 4 x CH), (127.42 / 7.25, 2 x CH), (129.64, 2 x C- q), (131.00, 2 x C-q), (133.61 , 2 x C-q), (134.20, 2 x C-q), (139.07, 2 x C-q), (142.90, 2 x C-q), (146.61 , 2 x C-q), (146.92, 2 x C-q), (147.41 , 2 x C-q), (150.47, 2 x C-q), (153.48, 2 x C-q), (155.04, 2 x C-q).

Example 9

N ⁴ ,N ⁴ '-bis(3,3-dimethyl-2,3-dihydrobenzofuran-5-yl)-N ⁴ ,N ⁴ '-bis(9,9-dimethyl-9H-fluoren- 2-yl )-[1 , 1 '-biphenyl]-4,4'-diamine

As described in the general procedure A, the aryl bromide 4,4'-dibromo-1 ,T-biphenyl (3.00 g, 9.6 mmol, 1.0 eq.) and the diarylamine from example 4 (7.18 g, 20.2 mmol, 2.1 eq.) were coupled in toluene (100 ml_), using sodium tert-butanolate (2.03 g, 21 .2 mmol, 2.2 eq.), Amphos (0.052 g, 0.19 mmol, 2 mol-%) and Pd ₂ (dba) ₃ (0.044 g, 0.05 mmol, 0.5 mol-%).

After cooling, aqueous ascorbic acid solution (5 %, 50 mL) was added to the reaction mixture followed by silica gel. The resulting mixture was filtered over a pad of silica gel which was then washed with toluene (300 mL). Evaporation to dryness provided the crude product as a yellowish solid (3.5 g, 40%) purity 72.1% (according to HPLC@340 nm).

Further washing of the silica pad with THF (300 mL) provided an additional crop of product (3.6 g, purity 94.8 % (HPLC@340 nm). Total yield: 86 %.

The combined crude products were further purified by column chromatography (heptane/ dichloromethane) to provide the product as a yellowish solid (4.2 g, 51%) purity 90.1 % according to HPLC@340 nm.

3.93 g of the chromatographed compound was finally purified by vacuum zone sublimation (10 ^-6 - 10‘ ⁷ mbar, 200-290°C) to give the title compound as a yellowish solid (2.26 g, purity up to 99.4% according to HPLC@340 nm).

¹³ C / ¹ H-NMR (101 MHz / 400 MHz (HSQC), CDCI3 : CS ₂ ): 8 / 8 (27.19 / 1.45, 4 x CH ₃ ), (27.57 / 1 .36, 4 x CH ₃ ), (42.03, 2 x C-q), (46.57, 2 x C-q), (84.76 / 4.27, 2 x CH ₂ ), (110.51 / 6.71 , 2 x CH), (117.23 / 7.15, 2 x CH), (119.44 / 7.57, 2 x CH), (120.61 / 6.98, 2 x CH), (120.69 / 7.51 , 2 x CH), (121.93 I 7.02, 2 x CH), (122.50 / 7.35, 2 x CH), (123.20 / 7.12, 2 x CH), (126.14 / 6.95, 2 x CH), (126.4517.22, 2 x CH), (127.19 / 7.28, 2 x CH), (127.29 / 7.42, 2 x CH), (133.28, 2 x C-q), (134.06, 2 x C-q), (137.66, 2 x C-q), (139.18, 2 x C-q), (140.90, 2 x C-q), (147.11 , 2 x C-q), (147.72, 2 x C-q), (153.17, 2 x C-q), (154.71 , 2 x C- q), (156.02, 2 x C-q).

Example 10

N ⁴ , N ⁴ '-bis(dibenzo[b,d]furan-2-yl)-N ⁴ ,N ⁴ '-bis(9,9-dimethyl-9H-fluoren-2-yl)-[1 ,T- biphenyl]-4,4'-diamine

As described in the general procedure A, the aryl bromide 2-bromodibenzo[b,d]furan (17.8 g, 72.1 mmol, 2.05 eq.) and the product from example 6 (20.0 g, 35.2 mmol, 1.0 eq.) were coupled in toluene (250 mL), using sodium tert-butanolate (7.10 g, 73.8 mmol, 2.1 eq.), Amphos (0.191 g, 0.703 mmol, 2 mol-%) and Pd ₂ (dba)3 (0.161 g, 0.176 mmol, 0.5 mol-%).

The product was worked up according to procedure B.

The crude product was purified by crystallization from acetone to provide the product as a yellowish solid (31.5 g, 99%) in a purity of 96.7% according to HPLC@340 nm. A second crystallization from toluene provided the product as a slightly yellowish solid with a purity of 97.8% according to HPLC@340 nm.

Additionally, the crude product was triturated twice with toluene/acetone to render the product as a slightly yellowish solid (22.5 g, 71 %) in a purity of 98.8% according to HPLC@340 nm.

5.51 g of the title compound was further purified by vacuum zone sublimation (10’ ⁶ - 10 ⁷ mbar, 240-340°C) to give the title compound as a slightly yellowish solid (3.59 g), purity up to 99.7% according to HPLC@340 nm.

Example 11 (alternative route for example 10)

N ⁴ ,N ⁴ '-bis(dibenzo[b,d]furan-2-yl)-N ⁴ ,N ⁴ '-bis(9,9-dimethyl-9H-fluoren-2-yl)-[1 ,T- biphenyl]-4,4'-diamine

The compound of example 10 can also be prepared via the alternative route of coupling 4,4’-dibromobiphenyl and the secondary amine from example 2 as follows:

As described in the general procedure A, the aryl bromide 4,4'-dibromo-1 ,T-biphenyl (4.50 g, 14.4 mmol, 1.0 eq.) and the diarylamine from example 2 (11.1 g, 29.6 mmol, 2.05 eq.) were coupled in toluene (100 mL), using sodium terf-butanolate (2.91 g, 30.3 mmol, 2.1 eq.), Amphos (0.078 g, 0.288 mmol, 2 mol-%) and Pd2(dba) ₃ (0.066 g, 0.072 mmol, 0.5 mol-%).

The product was worked up according to procedure D to give a first crop of product (7.5 g, 58%) purity 91.0% (according to HPLC@340 nm).

Further washing of the silica pad with THF (1400 mL) provided an additional crop of product (4.8 g, purity 99.3% (HPLC@340 nm). Total yield: 94%.

The crude products were combined and purified by crystallization from acetone/toluene to give the purified compound as yellowish solid (8.7 g, 67%) purity 98.2% (according to HPLC@340 nm).

¹³ C / ¹ H-NMR (101 MHz, 400 MHz (HSQC) CS ₂ : acetone-d ₆ 5:1): 5 / 8 (27.11 , 4 x CH ₃ ), (46.61 , 2 x C-q), (111.87 / 7.54, 2 x CH), (112.64 / 7.51 , 2 x CH), (117.95 / 7.27, 2 x CH), (117.97 / 7.80, 2 x CH), (119.63 / 7.59, 2 x CH), (120.98 / 7.57, 2 x CH), (121.04 / 7.83, 2 x CH), (122 60 / 7.36, 2 x CH), (122.75 / 7.09, 2 x CH), (123.01 / 7.29, 2 x CH), (123.58 / 7.18, 4 x CH), (124.21 , 2 x C-q), (125 49, 2 x C-q), (125.82 / 7.34, 2 x CH), (126.73 / 7.22, 2 x CH), (127.28 / 7.25, 2 x CH), (127.53 / 7.47, 4 x CH), (127.53 / 7.45, 2 x CH), (134.00, 2 x C-q), (134.43, 2 x C-q), (139.05, 2 x C-q), (143.27, 2 x C-q), (147.32, 2 x C- q), (147.63, 2 x C-q), (152.87, 2 x C-q), (153.22, 2 x C-q), (154.91 , 2 x C-q), (156.85, 2 x C-q).

Example 12

A/ ⁴ ,A/ ⁴ '-bis(dibenzo[b,d]thiophen-2-yl)-A/ ⁴ ,/ ⁴ '-bis(9,9-dimethyl-9H-fluoren-2-yl)-[1 , 1 '- biphenyl]-4,4'-diamine

As described in the general procedure A, the aryl bromide 4,4'-dibromo-1 ,1'-biphenyl (5.00 g, 16.0 mmol, 1.0 eq.) and the diarylamine from example 5 (12.9 g, 32.9 mmol, 2.05 eq.) were coupled in toluene (120 mL), using sodium tert-butanolate (3.23 g, 33.7 mmol, 2.1 eq.), Amphos (0.087 g, 0.32 mmol, 2 mol-%) and Pd2(dba) ₃ (0.074 g, 0.08 mmol, 0.5 mol-%).

After cooling, aqueous ascorbic acid solution (5 %, 100 mL) was added to the reaction mixture. The resulting pale green suspension was filtered, and the filter cake was washed twice with toluene (each times 55 mL).

The filter cake (crude product) was extracted with THF in a Soxhlet apparatus for 35 hours. Removal of the solvent from the extract provided the crude product as a green- yellowish solid (12.9 g, 86%). This residue was re-dissolved in o-dichlorobenzene (160 ml) and activated carbon (1 g Norit CGP Super) was added. Filtration over a pad of silica gave a clear yellow solution from which the solvent was removed on the rotavapor to provide the crude product as a yellowish solid (11.0 g, 74%) purity 96.8% (according to HPLC@340 nm).

5.63 g of the title compound was purified further by vacuum zone sublimation (1 O’ ⁶ — 10’ ⁷ mbar, 200-355°C) to give the title compound as a yellowish solid (3.75 g, purity up to 98.4% according to HPLC@340 nm).

¹³ C / ¹ H-NMR (101 MHz, 400 MHz (HSQC), CS ₂ : acetone-de 5:1 ): 5 / 6 (27.10 / 1.46, 4 x CH ₃ ), (46.63, 2 x C-q), (117.88 / 7.98, 2 x CH), (118.40 / 7.30, 2 x CH), (119.69 / 7.59, 2 x CH), (121.05 / 7.58, 2 x CH), (121.90 / 7.94, 2 x CH), (122.62 / 7.36, 2 x CH), (123.00 / 7.81 , 2 x CH), (123.15 / 7.12, 2 x CH), (123.72 / 7.75, 2 x CH), (124.07 / 7.22, 4 x CH), (124.64 / 7.39, 2 x CH), (125.02 / 7.33, 2 x CH), (126.82 I 7.22, 2 x CH), (127.08 / 7.43, 2 x CH), (127.30 / 7.26, 2 x CH), (127.65 / 7.49, 4 x CH), (134.31 , 2 x C-q), (134.37, 2 x C-q), (134.77, 2 x C-q), (135.30, 2 x C-q), (136.98, 2 x C-q), (138.99, 2 x C-q), (140.52, 2 x C-q), (145.09, 2 x C-q), (147.02, 2 x C-q), (147.27, 2 x C-q), (153.24, 2 x C-q), (154.97, 2 x C-q).

Example 13 (comparative example, not inventive)

N ⁴ ,N ⁴ ,N ⁴ ',N ⁴ '-tetrakis(9,9-dimethyl-9H-fluoren-2-yl)-2,2'-dimethyl -[1 ,T-biphenyl]-4,4'- diamine As described in general procedure A, the aryl bromide from example 1 (5 00 g, 14.7 mmol, 1.0 eq.) and the diarylamine bis(9,9-dimethyl-9H-fluoren-2-yl)amine (12.1 g, 30.1 mmol, 2.05 eq.) were coupled in toluene (100 mL), using sodium ferf-butanolate (2.97 g, 30.9 mmol, 2.1 eq.), tri tert-butylphosphonium tetrafluoroborate (0.043 g, 0.15 mmol, 1 mol-%) and Pd2(dba)3 (0.034 g, 0.04 mmol, 0.25 mol-%).

After cooling, aqueous ascorbic acid solution (5 %, 100 mL) was added to the reaction mixture.

The resulting suspension was filtered and the residue was washed with toluene (20 mL) and acetone (15 mL). The residue was dissolved in chlorobenzene and activated carbon (Norit CGP Super) was added.

It was then filtered over a pad of Celite and the product rinsed down with chlorobenzene. From the filtrates, the solvent was removed to provide the crude product as a green- yellowish solid (13.3 g, 92%).

The crude product was further purified by crystallization from acetone to provide the product as a yellowish solid (10.1 g, 70%) in a purity of 99.4% according to HPLC@340 nm.

¹³ C / ¹ H-NMR (101 MHz, 400 MHz (HSQC) CS ₂ : acetone-d ₆ 5:1): 8 / 5 (20.29 / 2.12, 2 x CH ₃ ), (27.07 / 1 .46, 8 x CH ₃ ), (46.57, 4 x C-q), (118.57 / 7.29, 4 x CH), (119.63 / 7.59, 4 x CH), (120.91 / 7.57, 4 x CH), (121.70 / 7.06, 2 x CH), (122.60 / 7.36, 4 x CH), (123.21 / 7.11 , 4 x CH), (125.66 / 7.12, 2 x CH), (126.73 / 7.22, 4 x CH), (127.28 / 7.27, 4 x CH), (130.79 / 7.07, 2 x CH), (134.11 , 4 x C-q), (135.83, 2 x C-q), (137.05, 2 x C-q), (139.08, 4 x C-q), (146.77, 2 x C-q), (147.49, 4 x C-q), (153.20, 4 x C-q), (154.77, 4 x C-q).

Example 14

N ⁴ ,N ⁴ '-bis(dibenzo[b,d]furan-2-yl)-N ⁴ ,N ⁴ '-bis(9,9-dimethyl-9H-fluoren-2-yl)-2,2'-dimethyl- [1 , 1 '-biphenyl]-4,4'-diamine

As described in the general procedure A, the aryl bromide from example 1 (5.00 g, 14.7 mmol, 1.0 eq.) and the diarylamine from example 2 (11.3 g, 30.1 mmol, 2.05 eq.) were coupled in toluene (100 mL), using sodium ferf-butanolate (2.97 g, 30.9 mmol, 2.1 eq.), tri tert butylphosphonium tetrafluoroborate (0.011 g, 0.037 mmol, 0.25 mol-%) and Pd ₂ (dba) ₃ (0.014 g, 0.015 mmol, 0.1 mol-%).

After cooling, acetic acid (1 mL) and water (50 mL) were added to the reaction mixture. The mixture was filtrated and phases were separated. The organic layer was washed with water, filtered and azeotropic distilled with toluene.

The crude product was purified by crystallization from toluene/acetone to provide the product as an off white solid (11.1 g, 82%) in a purity of 99.0% (according to HPLC@340 nm).

¹³ C / ¹ H-NMR (101 MHz, 400 MHz (HSQC) CS ₂ : acetone-d ₆ 5:1): 8 / 8 (20.38 / 2.12, 4 x CH ₃ ), (27.12 / 1 .46, 2 x CH ₃ ), (46.59, 2 x C-q), (111 .88 / 7.54, 2 x CH), (112.62 / 7.52, 2 x CH), (117.80 / 7.27, 2 x CH), (118.12 / 7.82, 2 x CH), (119.59 / 7.59, 2 x CH), (120.69 I 7.04, 2 x CH), (120.92 / 7.57, 2 x CH), (121.04 / 7.83, 2 x CH), (122.60 / 7.36, 2 x CH), (122.60 / 7.10, 2 x CH), (122.99 / 7.29, 2 x CH), (124.26, 2 x C-q), (124.63 / 7.07, 2 x CH), (125.49, 2 x C-q), (125.99 / 7.36, 2 x CH), (126.66 / 7.21 , 2 x CH), (127.28 / 7.26, 2 x CH), (127.52 / 7.45, 2 x CH), (130.84 / 7.05, 2 x CH), (133.74, 2 x C-q), (135.30, 2 x C-q), (137.06, 2 x C-q), (139.12, 2 x C-q), (143.44, 2 x C-q), (147.32, 2 x C-q), (147.95, 2 x C-q), (152.86, 2 x C-q), (153.20, 2 x C-q), (154.84, 2 x C-q), (156.86, 2 x C-q).

Example 15 (comparative example according to EP 0879868 A2) N ⁴ ,N ⁴ ’-bis(9,9-dimethyl-9H-fluoren-2-yl)-N ⁴ ,N ⁴ '-di(pyridin-3-yl)-[1 ,1 ’-biphenyl]-4,4'- diamine

Example 15 step 1 )

N-(9,9-dimethyl-9H-fluoren-2-yl)pyridin-3-amine

This secondary amine was synthesized via the coupling of 2-bromo-9,9-dimethyl-9H- fluorene with pyridin-3-amine. The product was obtained as colorless crystals (99.8% purity according to HPLC@340 nm) in 29% yield.

¹³ C / ¹ H-NMR (101 MHz / 400 MHz (HSQC), CS ₂ : acetone-d ₆ 5:1 ): 5 / 5 (27.19 / 1.48, 2 x CH ₃ ), (46.51, C-q), (112.35 / 7.1.85, CH), (117.05 / 7.05, CH), (119.27 / 7.54, CH), (121.03 I 7.55, CH), (122.07 / 7.46 ddd CH), (122.51 / 7.35 d H-8, CH), (123.48 / 7.12 dd, CH), (126.35 / 7.18 tr, CH), (127.20 / 7.24 tr, CH), (132.80, C-q), (139.35, C-q), (139.98 / 8.37, 8.05, Ar CH), (142.20, C-q), (152.82, C- q), (155.04, C-

Example 15 step 2)

N ⁴ ,N ⁴ '-bis(9,9-dimethyl-9H-fluoren-2-yl)-N ⁴ ,N ⁴ '-di(pyridin-3-yl)-[1 ,T-biphenyl]-4,4'- diamine

As described in the general procedure A, the aryl bromide 4,4'-dibromo-1 ,T-biphenyl (4.95 g, 15.9 mmol, 1.0 eq.) and the diarylamine from Example 15 Step 1 ) N-(9,9’- dimethylfluoren-2-yl)pyridin-3-amine (9.2 g, 32 mmol, 2.02 eq.) were coupled in toluene (100 mL), using sodium fert-butanolate (1.60 g, 33.3 mmol, 2.1 eq.), tris-tert- butylphosphonium tetrafluoroborate (0.105 g, 0.317 mmol, 2 mol-%) and Pd ₂ (dba) ₃ (0.0726 g, 0.0793 mmol, 0.5 mol-%).

The product was worked up according to procedure C.

Purification of the crude product (14.6 g of a brown foam) by column chromatography on silica (eluent: ethyl acetate:heptane 1 : 1 to 9:1 ) provided in the main fraction the product (7.2 g) with a purity of 98.5% according to HPLC@340 nm.

5.26 g of the title compound was further purified by vacuum zone sublimation (1 O’ ⁶ — 10' ⁷ mbar, 240-295°C) to give the title compound as a yellowish solid (3.93 g, purity up to 99.8% according to HPLC@340 nm.

¹³ C / ¹ H-NMR (101 MHz / 400 MHz (HSQC), CS ₂ : acetone-d ₆ 5:1 ): 6 / 5 (27.02 / 1.47 2 CH ₃ ), (46.68 q-C), (118.93 / 7.34 CH), (119.86 / 7.70 CH), (121.24 / 7.71 CH), (122.65 / 7.45 CH), (123.57 / 7.24 CH), (123.67 / 7.10 CH), (124.31 / 7.20 2 CH), (127.08 / 7.27 CH), (127.33 / 7.31 CH), (127.87 / 7.592 CH), (129.41 / 7.47 CH), (135.28 q-C), (135.38 q-C), (138.75 q-C), (143.28 / 8.22 2 CH), (143.94 q-C), (145.56 / 8.43 2 CH), (146.14 q- C), (146.15 q-C), (153.29, q-C); (155.22 q-C). III Application examples

III. a) HOMO and LUMO levels of the hole transport materials

Determination of HOMO by cyclic voltammetry

The onset method was mainly used for the analysis of samples which did not show a clear redox event or only one of the two events. To evaluate the HOMO, linear extrapolation (using IVIIIM Soft) was used to determine the E _ons via a tangent to the slope of the oxidation event. The intersection between the tangent line and the starting slope was used for the further calculation of the HOMO.

Ferrocene was used as the reference system, from which the Fermi energy level (4.4 eV) was determined on the day of each measurement to avoid deviation within the measurement series. With reference to the reference system, the HOMO was determined by the formula [1]:

[1] ^Homo ^{= —} I^OTIS + 4.4 e7|

E1/2 method

Alternatively, the EI/ ₂ method for evaluating the HOMO was used for completely reversible redox events. First, the basic parameters of the cyclovoltammogram were determined (MUM Soft) and E-i/ ₂ was calculated from them. The value obtained was used to determine the HOMO in formula [1] (instead of the Eon).

Determination of the HOMO-LUMO-GAP by UV/VIS spectroscopy.

To determine the optical band GAP A _O n _S , a tangent (with the slope determined at the inflection point) was drawn at the inflection point (determined by Origin 2020 or the 1 derivative using Excel) of the falling edge of the longest wavelength absorption band. The intersection point with the abscissa is called the optical onset (Aons) and corresponds to the energy between HOMO and LUMO. From E = h * c / A, follows E _gop t [eV] = 1240 / Aons [nm]. The LUMO is calculated from the level of the HOMO by addition of the band gap.

Table of HOMO- and LUMO-Levels of the compounds lll.b) Conductivities of the hole transport materials

The conductivities were measured using NDP-9 as the p-dopant. Glass substrates (35 mm x 50 mm) were thoroughly cleaned and then coated with a 155-nm-thick layer of indium tin oxide (ITO) having trenches with a width of 20 pm, i.e. a trench separated two ITO sections. The trench was filled with the compound of formula (I) and NDP-9 as p- dopant material by co-evaporation of the compound of formula (I) and the p-dopant material. Each doped layer had a thickness of 50 nm. After applying a voltage from 10 V between two ITO stripes, the conductivity was determined.

For each doping ratio (1%, 3% and 5% by volume), conductivity was determined for two different sample geometries (sample geometry A having a length of trench of 188 mm; sample geometry B having a length of trench of 146 mm), whereby the sample to be tested contained both geometries.

Table of compounds (I) with their glass temperature T _g or melting temperature T _m and their conductivities at the respective ratio of dopand NDP-9 Comparative example 15 shows that compounds that bear two pyridyl groups (i.e. heterocyclic groups that have only one single nitrogen atom) have poorer conductivities than the compounds according to the invention.