TRANSITION METAL COMPLEXES COMPRISING ASYMMETRIC TETRDENTATE LIGANDS

[0001] The present invention relates to light emitting transition metal complexes comprising asymmetric tetradentate ligands and their use for the manufacture of organic electronic devices.

[0002] US 2005/170206 discloses organic light emitting devices comprising

transition metal complexes based on multidentate ligands. Symmetric tetradentate ligands wherein two 2-phenylpyridine ligand units are connected via a linker are mentioned. This reference mentions that multidentate ligands should improve the kinetic stability of the transition metal complexes manufactured using same compared to isolated bidentate ligands.

[0003] WO 2008/096609 discloses carbene ligand units suitable for

manufacturing transition metal complexes with two identical bidentate carbene ligand units being connected through an alkylene bridge.

[0004] US 2008/286605 discloses a symmetrical N, N\ O, O' dianionic

tetradentate ligand resulting from the deprotonation of 2,2'-(2,2'-bipyricline- 6,6'-diyl)diphenol and transition metal complexes derived therefrom (cpd. D-29, page 48).

[0005] WO 2006/061 182 discloses platinum complexes with symmetrical

tetradentate ligands which are composed of two identical bidentate ligand units linked through a linker.

[0006] US 2010/0171417 discloses platinum complexes with tetradentate ligands comprising two identical or two different bidentate ligand units as phosphorescent materials in combination with certain charge transport materials useful in the manufacture of organic electronic devices.

[0007] Today, various light-emitting devices are under active study and

development, in particular those based on electroluminescence (EL) from organic materials.

[0008] As a first example, light emitting electrochemical cells (often referred to as LEEC or LEC) may be mentioned. LEECs are solid state devices which generate light from an electric current. LEECs are usually composed of two metal electrodes connected by an organic semiconductor containing mobile ions.

[0009] Aside from the mobile ions, the structure of LEECs is similar to a second group of light emitting organic electronic devices which are commonly referred to as organic light emitting diodes (OLEDs).

[0010] In the contrast to photoluminescence, i.e. the light emission from an active material as a consequence of optical absorption and relaxation by radiative decay of an excited state, electroluminescence (EL) is a nonthermal generation of light resulting from the application of an electric field to a substrate. In this latter case, excitation is accomplished by

recombination of charge carriers of opposite signs (electrons and holes) injected into an organic semiconductor in the presence of an external circuit.

[001 1] A simple prototype of an organic light-emitting diode (OLED), i.e. a single layer OLED, is typically composed of a thin film of an active organic material which is sandwiched between two electrodes, one of which needs to have a degree of transparency sufficient in order to observe light emission from the organic layer.

[0012] If an external voltage is applied to the two electrodes, charge carriers, i.e. holes, at the anode and electrons at the cathode are injected to the organic layer beyond a specific threshold voltage depending on the organic material applied. In the presence of an electric field, charge carriers move through the active layer and are non-radiatively discharged when they reach the oppositely charged electrode. However, if a hole and an electron encounter one another while drifting through the organic layer, excited singlet and triplet states, so-called excitons, are formed. Light is thus generated in the organic material from the decay of molecular excited states (or excitons). For every three triplet excitons that are formed by electrical excitation in an OLED, only one state with antiparallel spin, S=0 (singlet) exciton is created. [0013] Many organic materials exhibit fluorescence (i.e. lunninescence from a spin -allowed process) from singlet excitons; since this process occurs between states of same spin multiplicity it may be very efficient. On the contrary, if the spin multiplicity of an exciton is different from that of the ground state, then the radiative relaxation of the exciton is spin forbidden and

luminescence will be slow and inefficient. Because the ground state is usually a singlet, decay from a triplet is spin-forbidden (different spin multiplicity) and efficiency of EL is very low. Thus the energy contained in the triplet states is mostly wasted.

[0014] Phosphorescence emission is a phenomenon of light emission in the

relaxation process between two states of different spin multiplicity, often between a triplet and a singlet, but because the relaxation process is normally conducted by thermal deactivation, it is in many cases not possible to observe phosphorescence emission at room temperature. Characteristically, phosphorescence may persist for up to several seconds after excitation due to the low probability of the transition, in contrast to fluorescence which originates in the rapid decay.

[0015] The theoretical maximum internal quantum efficiency of light-emitting

devices comprising light-emitting materials based on an emission phenomenon in the relaxation process from a singlet excited state, (i.e. fluorescence emission), is at maximum 25 %, because in organic EL devices the ratio of the singlet to the triplet state in the excited state of light-emitting materials is always appr. 25:75. By using phosphorescence (emission from triplet states) this efficiency could be raised to the theoretical limit of 100 %, thereby significantly increasing the efficiency of the EL device.

[0016] As mentioned above, it is difficult to get phosphorescence emission from an organic compound because of low probability of intersystem crossing and concurrent thermal deactivation of the triplet relaxation process.

However, it has been found that the presence of heavy atoms favours spin orbit coupling and therefore intersystem crossing is enhanced. This is also true when organic ligands are coordinated to heavy metals, showing spin- orbit interaction resulting from the heavy metal atom effect.

[0017] The wavelength of the light emitted is governed by the structure and the combination of ligands in the transition metal complex.

[0018] One of the challenges still to be satisfactorily solved in organic light

emitting devices is the availability of suitable transition metal complexes providing sufficient stability in operating devices on one hand and desired photoactive properties on the other hand.

[0019] Accordingly there is still a need for phosphorescent transition metal

complexes having improved stability, especially those emitting in the blue region, to obtain highly efficient and long term stable devices.

Furthermore, to realize large area display and lighting applications at low cost, it is of interest to develop new emitters with sufficient solubility in suitable solvents to enable processing from solution, such as roll-to-roll printing, as the majority of known phosphorescent emitters are not soluble enough in organic solvents.

[0020] It was thus an object of the present invention to provide new transition metal complexes comprising tetradentate ligands useful in the

manufacture of organic light emitting devices.

[0021] This object has been achieved with the transition metal complexes in accordance with claim 1 with a subunit comprising an asymmetric tetradentate ligand.

[0022] Preferred embodiments of the present invention are set forth in the

dependent claims and the detailed specification hereinafter.

[0023] The light emitting transition metal complexes in accordance with the

present invention comprise a transition metal M with an atomic number of at least 40 and having a coordination number equal to six, preferably selected from Ir, Rh, Re, Os or Ru and particularly preferred Ir, and a subunit with an asymmetric tetradentate ligand comprising two different bidentate ligand units L ¹ and L ² and represented by general formula (1 ) wherein q, and r, independent of one another are 0 or 1 , preferably at least one of q and r being 1 and even more preferred q and r both being 1 , the pending arm units B ¹ and B ² , independent of one another are represented by general formula (2)

wherein Z ¹ is a divalent group selected from the group consisting of -O-,

-S-, -NR ⁵ -, -BR ⁶ -, -PR ⁷ -, -P(=O)R ⁸ -, -SiR ⁹ R ¹⁰ - , -N(R ¹¹ )-C(=O)-,

-N=C(R ¹² )-, -C(=O)-, -C=NR ¹³ -, -C(=S)- and -P(=S)(R ¹⁴ )-,

wherein R ¹ to R ¹⁴ , which may be the same or different at each occurrence, are selected from hydrogen, halogen, NO2, CN, NH ₂ , NHR', N(R')2,

B(OH) ₂ , B(OR') ₂ , CHO, COOH, CONH ₂ , CON(R') ₂ , CONHR', SO ₃ H,

C(=O)R', P(=O)(R') ₂ , S(=O)R', S(=O) ₂ R', P(R') ₃ ⁺ , N(R') ₃ ⁺ , OR', SR' and alkyl, haloalkyl, aryl, aralkyl or heteroaryl groups with R' being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups

n, m and p, independently of one another, are integers of from 0 to 8, the sum of n+m+p being at least 1 , and

wherein at least one of the L ¹ and L ² bidentate ligand units is represented by formula (3),

wherein

Ei represents a nonmetallic atom group required to form a 5- or

6-membered heteroaromatic ring, optionally condensed with additional aromatic moieties or non aromatic cycles, said ring optionally having one or more substituents, optionally forming a condensed structure with the ring comprising E2, and

E2 represents a nonmetallic atom group required to form a 5- or

6-membered aromatic or heteroaromatic ring, optionally condensed with additional aromatic moieties or non aromatic cycles, said ring optionally having one or more substituents, optionally forming a condensed structure with the ring comprising Ei. and

wherein the ring Ei is bound to the transition metal via a neutral donor atom which is a carbon in the form of a carbene or a heteroatom, preferably a nitrogen atom, and the ring E2 is bound to the transition metal through a carbon atom having formally a negative charge or through a nitrogen atom having formally a negative charge and wherein

bivalent linking central scaffold A is selected from compounds of general formulae (4) to (7)

[0025] (V)

wherein

Z ² is CR ₂ , NR, R ₂ N ⁺ , RB, R ₂ B- , RP, RP(O), SiR ₂ , RAI, R ₂ Ah, RAs, RAs(O), RSb, RSb(O), RBi, RBi(O), O, S, Se or Te or a substituted or

unsubstituted 5- or 6-membered carbocyclic, aromatic or heteroaromatic ring; preferably Z ² is CR ₂ , RN, -O-, -S-, RB, RP, RP(O), SiR ₂ or a substituted or unsubstituted 5- or 6-membered carbocyclic, aromatic or heteroaromatic ring.

[0026] In accordance with an embodiment of the present invention, Z ² is

preferably a substituted or unsubstituted 5- or 6-membered carbocyclic, aromatic or heteroaromatic ring (which may carry substituents other than hydrogen). The heterocyclic rings may comprise one or more heteroatoms, preferably selected from O, N, S, P and Si, with O, N and S being particularly preferred.

[0027] In accordance with another preferred embodiment Z ² is a substituted or unsubstituted 5- or 6-membered carbocyclic, aromatic or heteroaromatic ring (which may carry substituents other than hydrogen) selected from the group consisting of

cyclopenta-1,3- 2H- rrole 3H- rrole lH-imidazole - azole

lH-l ,2,3-triazole 3H-l ,2,4-triazole 2H-l ,2,3-triazole lH-tetrazole

2H-tetrazole lH-pyrazole oxazole isoxazole thiazole isothiazole

benzene pyridazine pyrimidine pyrazine pyridine

1 ,2,3-triazine 1 ,3,5-triazine 1 ,2,4-triazine

[0028]

cyclopentane cyclohexane

[0029] ^c y ^c l° ^nexa_ 1 -diene cyclohexa- 1 ,4-diene

[0030] 6-membered carbocyclic, aromatic or heteroaromatic rings being

preferred, in particular Z ² is a cyclohexane ring, a benzene ring, a pyridine ring, a pyrimidine ring, a 1 ,3,5- or 1 ,2,3-triazine ring,

[0031] Z ³ and Z ⁴ are CR ₂ , NR, R ₂ N ⁺ , RB, R ₂ B- , RP, RP(O), SiR ₂ , RAI, R ₂ AI-, RAs, RAs(O), RSb, RSb(O), RBi, RBi(O), O, S, Se or Te, preferably Z ³ and Z ⁴ are CR ₂ , NR, -O-, -S-, RB, RP, RP(O) or SiR _2; particularly preferred Z ³ is CR ₂ , NR, RB RP, RP(O) and SiR ₂ , particularly preferred Z ⁴ is CR ₂ , NR, O, S and SiR ₂ .

[0032] Z ⁵ is CR, N, RN ⁺ , B, RB-, P, P(O), SiR, Al, RAh, As, As(O), Sb, Sb(O), Bi, Bi(O), preferably CR, N, B, P, P(O) and SiR and

R, which may be the same or different at each occurrence, is selected from the group consisting of hydrogen, alkyl, haloalkyi, aralkyl, aryl and heteroaryl.

[0033] Preferred alkyl groups R which includes cycloalkyi groups are Ci to C ₂ o, preferably Ci to Cio and particularly preferably Ci to C6 alkyl groups, most preferred being methyl, ethyl, i-propyl, n-propyl, n-, i- and t-butyl, cyclopentyl, cyclohexyl and Cio adamantyl groups.

[0034] Preferred haloalkyi groups R are based on the preferred alkyl groups

defined above, wherein one or more of the hydrogen atoms have been replaced by one or more halogen atoms. Accordingly, preferred haloalkyi groups are based on Ci to C ₂ o, preferably Ci to Cio and particularly preferably Ci to C6 alkyl groups, most preferred being methyl, ethyl, i- propyl, n-propyl, n-, i- and t-butyl, cyclopentyl, cyclohexyl and Cio

adamantyl groups.

[0035] Preferred aralkyl groups R comprise alkyl groups as defined before

wherein one or more of the hydrogen atoms have been replaced by an aryl group, preferably as defined below. The total number of carbon atoms in the aralkyl groups is between 5 and 50, preferably between 6 and 35 and particularly preferred between 6 and 25 carbon atoms. One or more carbon atoms in the aryl rings may be replaced by a heteroatom, e.g. N, O or S.

[0036] Preferred aryl groups R are 5- or 6-membered aromatic ring systems, which may carry one or more substituents other than hydrogen. Two or more rings may be annealed to form condensed structures or two and more aryl groups may be connected through a chemical bond. Examples for preferred aryl groups are phenyl, naphthyl, biphenyl, triphenyl and anthracenyl. [0037] Preferred heteroaryl groups R are ring systems as described above for aryl rings wherein one or more of the ring carbon atoms has been replaced by a heteroatom, preferably selected from N, O and S. Preferred heteroaryl groups R are based on rings selected from the group consisting of

2H-pyrrole 3H-pyrrole lH-imidazole 2H-imidazole

.A.

\j \J J J lH-l,2,3-triazole 3H-l,2,4-triazole 2H-l,2,3-triazole lH-pyrazole

oxazole isoxazole thiazole isothiazole

pyridazine pyrimidine pyrazine pyridine

1,2,3-triazine 1,3,5-triazine 1,2,4-triazine

[0038]

[0039] Preferred aryl and heteroaryl ring systems R comprise of from 1 to 50, preferably of from 1 to 30 and particularly preferable of from 1 to 20 carbon atoms.

[0040] In yet another preferred embodiment, central scaffold A comprises a

moiety which is known to make part of a host or a hole or electron transport materials used in OLEDs. Such preferred moeties are pyridine, pyrimidine, triazine, carbazole, dibenzofuran and dibenzothiophene heteroaryl ring. Other preferred moieties correspond to triphenylamine, triphenylsilyl, triarylboron and phosphine oxide groups.

[0041] In the formulae (4) to (7) given above ^* denotes the two bonding sites of the bivalent central scaffold A through which bidentate ligand units L ¹ and L ² are bonded either directly or through arm units B ¹ and B ² (q and r being 1 in this case).

[0042] A is particularly preferably a CR ₂ , RN, -O-, -S-, RB, RP, RP(O), SiR ₂ group or a five or six membered carbocyclic, aromatic or heteroaromatic ring in which the arm units Bi and B2, if present, may be attached to the ring in any combination of positions, A represents particularly preferably CR2, RN, RB, RP(O), S1R2 group or a five or six membered ring system selected from the group consisting of

cyclopenta-l,3-diene 2H-pyrrole 3H-pyrrole

lH-imidazole 2H-imidazole lH-L2,3-triazole

3 -l,2,4-triazole 2H-l,2,3-triazole lH-pyrazole

oxazole isoxazole thiazole isothiazole

benzene pyridazine pyridine pyrazine pyridine

[0043] 1,2,3-triazine 1,3,5-triazine 1,2,4-triazine

cyclopentane cyclohexane

[0044] cyclohexa- 1, 3 -diene cyclohexa- 1 ,4-diene [0045] In accordance with a further preferred embodiment A is a six membered carbocyclic, aromatic or heteroaromatic ring, in particular a cyclohexane ring, a benzene ring, a pyridine ring, a pyrimidine ring, a 1 ,3,5- or 1 ,2,3- triazine ring to which arm units B ¹ and B ² (if present), respectively L ¹ and L ² bidentate ligand units are preferably bound in 1 ,3 meta position to each other.

[0046] In still another preferred embodiment, arm units B ¹ and B ² (if present) respectively L ¹ and L ² bidentate ligand units are bound in 1 ,4 para position to each other of an aryl or heteroaryl ring, in particular of a cyclohexane ring, a benzene ring, a pyridine ring, a pyrimidine ring, a 1 ,3,5- or 1 ,2,3- triazine ring

[0047] The bonding of arm units B ¹ and B ² respectively L ¹ and L ² bidentate ligand units in 1 ,2 ortho position to each other is less preferred compared to 1 ,3 and 1 ,4-bonding for sterical reasons.

[0048] In accordance with another preferred embodiment, bivalent central

scaffold A is selected from formula (5) in which the arm units B ¹ and B ² (if present) or the two ligand units L ¹ and L ² directly are attached to the phenyl rings in any combination of positions, as shown in the formula.

[0049] In accordance with a further preferred embodiment, A is selected from formula (5) wherein the arm units B ¹ and B ² (if present) or the two ligand units L ¹ and L ² directly are attached to the phenyl rings in para positions to the Z ³ atom.

[0050] In accordance with another preferred embodiment, bivalent central

scaffold A is selected from formulae (6) to (7) in which the arm units B ¹ and B ² (if present) or the two ligand units L ¹ and L ² directly are attached to the benzene rings in any combination of positions, as shown in the formulae. In accordance with a further preferred embodiment, A is selected from formulae (6) to (7) wherein the arm units B ¹ and B ² (if present) or the two ligand units L ¹ and L ² directly are attached to the benzene rings in para positions to the Z ⁴ and Z ⁵ atoms. [0051] The arm units B ¹ and B ² , which may be the same or different at each occurrence, may be any divalent bridging group represented by formula (2) given above.

[0052] Preferred groups B ¹ and B ² are selected from alkylene groups having of from 1 to 8 carbon atoms, i.e. groups of formula (2) wherein m and p are zero and n is an integer of from 1 to 8, particularly preferred from alkylene groups having of from 2 to 4 carbon atoms.

[0053] In certain cases it has proven to be advantageous if , in addition to an alkylene chain an element Z ¹ is present (i.e. m is 1), which in this case is preferably -O-, -S-, -NR ⁵ -, -BR ⁶ -, -PR ⁷ -, -P(=O)R ⁸ -, -SiR ⁹ R ¹⁰ - , -N(R ¹¹ )-, -C(=O)-, -N=C(R ¹² )-, -C(=O)-, -C=NR ¹³ - with R ⁵ to R ¹³ as defined hereinabove, in particular -O-, -S-, -NR ⁵ -, -N(R ¹¹ )-C(=O)-, -N=C(R ¹² )-, -C(=O)-, -C=NR ¹³ - with R ⁵ to R ¹³ as defined hereinabove.

[0054] In accordance with another preferred embodiment B ¹ and/or B ² represent a group of formula (2) with n being an integer of from 1 to 8, m being 1 and p being an integer of from 1 to 8, i.e. wherein two alkylene groups are separated by a group Z ¹ as defined above.

[0055] In accordance with still another embodiment arm units B ¹ and B ² comprise a structural element -Ch -NH-, -CH2-CH2-NH-, -CH ₂ -N(CH ₃ )-, -Ch -NH- CH ₂ -, -N(CH ₃ )-CH ₂ , -CH ₂ -CH ₂ -NH-C(=O)-, -CH ₂ -NH-C(=O)- and the equivalent structural elements wherein one or more of the hydrogen atoms attached to carbon atoms are replaced by methyl or ethyl.

[0056] The sum of n+m+p is at least 1 , preferably n and p independently of one another are integers of from 0 to 8, preferably of from 0 to 4 and m is preferably 0 or 1.

[0057] For the purpose of the present invention, the tetradentate ligands of the subunits of the light emitting transition metal complexes of the present invention are asymmetric due to the fact that they comprise two bidentate ligand units L ¹ and L ² which differ from each other, e.g. by their

composition, their Ei and E ₂ ring structure, their nature and position of the linking between rings Ei and E ₂ , their substituents or the positions at which these substituents are attached. For the purposes of the present invention tetradentate ligands which involve bidentate ligand units which are identical but are bound to central scaffold A or to pending arm units B ¹ and B ² , if present, through different positions are not deemed to be asymmetric in accordance with the present invention. Tetradentate ligands which involve bidentate ligand units L ¹ and L ² showing any other difference are deemed to be asymmetric in accordance with the present invention.

[0058] The bidentate ligand units L ¹ and L ² may be bound to arm units B ¹ and B ² , if present, or to central scaffold A through any position or in any manner which does not interfere with those positions through which the bidentate ligand units L ¹ and L ² are bound to the transition metal in the light emitting transition metal complexes in accordance with the present invention.

[0059] The asymmetric tetradentate ligands forming part of the subunit of the light emitting transition metal complexes in accordance with the present invention comprise two bidentate ligand units L ¹ and L ² which differ from each other as defined hereinbefore and which are linked to each other through central scaffold A and, if present to arm units B ¹ and B ² as defined hereinbefore.

[0060] In principle any ligand unit described in the prior art as bidentate ligand for transition metal complexes may be present in the light emitting transition metal complexes in accordance with the present invention. Thus, reference may be made to the prior art documents describing such ligands. At least one of the ligand units L ¹ or L ² is, however, represented by formula (3) as defined above.

[0061] In accordance with the present invention, the E1 ring is bound to the

transition metal via a neutral donor atom which is a carbon in the form of a carbene or a heteroatom, preferably a nitrogen atom, and ring E2 is bound to the transition metal through a carbon atom having formally a negative charge or through a nitrogen atom having formally a negative charge. The E1 ring is a 5 to 6-membered heteroaryl ring containing at least one donor nitrogen atom. Said ring may be un-substituted or substituted by substituents selected from the group consisting of halogen, NO2, CN , NH2, NHR ¹⁵ , N(R ¹⁵ ) ₂ , B(OH) ₂ , B(OR ¹⁵ ) ₂ , CHO, COOH, CONH ₂ , CON(R ¹⁵ ) _2j CONHR ¹⁵ , SO ₃ H, C(=O)R ¹⁵ , P(=O)(R ¹⁵ ) ₂ , S(=O)R ¹⁵ ,

S(=O) ₂ R ¹⁵ , P(R ¹⁵ )s ⁺ , N(R ¹⁵ ) ₃ ⁺ , OR ¹⁵ , SR ¹⁵ , Si(R ¹⁵ ) ₃ , and alkyl, haloalkyl, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl groups with R ¹⁵ being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups and/or may form an annealed ring system with other rings selected from

cycloalkyl, aryl and heteroaryl rings. Heteroaryl substituents may be preferably un-substituted or substituted carbazolyl or un-substituted or substituted dibenzofuranyl.

[0062] More particularly Ei is a heteroaryl ring derived from the heteroarenes group consisting of 2H-pyrrole, 3H-pyrrole, 1 H-imidazole, 2H-imidazole, 4H-imidazole,1 H-1 ,2,3-triazole, 2H-1 ,2,3-triazole, 1 H-1 ,2,4-triazole, 1 H- pyrazole, 1 H-1 ,2,3,4-tetrazole, imidazol-2-ylidene, oxazole, isoxazole, thiazole, isothiazole, 1 ,2,3-oxadiazole, 1 ,2,5-oxadiazole, 1 ,2,3- thiadiazole, 1 ,2,5-thiadazole, pyridazine, pyridine, pyrimidine, pyrazine, 1 ,2,3-triazine, 1 ,2,4-triazine, 1 ,3,5-triazine, 1 ,2,3,4-tetrazine, 1 ,2,4,5-tetrazine and

1 ,2,3,5-tetrazine rings, which may be unsubstituted or substituted as defined above.

[0063] In accordance with a further preferred embodiment the ring E ₂ is selected from the group consisting of substituted or un-substituted Cs-C ₃ o aryl and substituted or un-substituted C ₂ -C ₃ o heteroaryl groups, which E ₂ group may be un-substituted or substituted by substituents selected from the group consisting of halogen, NO ₂ , CN, NH ₂ , NHR ¹⁵ , N(R ¹⁵ ) ₂ , B(OH) ₂ , B(OR ¹⁵ ) ₂ , CHO, COOH, CONH ₂ , CON(R ¹⁵ ) ₂ , CONHR ¹⁵ , SO ₃ H, C(=O)R ¹⁵ , P(=O)(R ¹⁵ ) ₂ , S(=O)R ¹⁵ , S(=O) ₂ R ¹⁵ , P(R ¹⁵ ) ₃ ⁺ , N(R ¹⁵ ) ₃ ⁺ , OH, OR ¹⁵ , SR ¹⁵ , Si(R ¹⁵ ) ₃ and alkyl, haloalkyl, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl groups as defined hereinabove with R ¹⁵ being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups

[0064] Ei and E ₂ may be linked through a divalent linking group or through a

covalent bond, which has proved to be advantageous in certain cases.

[0065] In the following a number of preferred embodiments of the present

invention will be described in more detail. [0066] According to a first preferred embodiment at least one of bidentate ligand units L ¹ and L ² is represented by formulae (8) to (10)

(8) (9) (10) wherein

X5 is a neutral donor atom via which the 5- or 6-membered heteroaromatic ring Ei is bonded to the metal and which is a carbon in the form of a carbene or a heteroatom, preferably a nitrogen atom, X ₇ is a carbon atom having formally a negative charge or a nitrogen atom having formally a negative charge via which the 5- or 6-membered aromatic or

heteroaromatic ring E2 is bound to the metal,

Xi , X2, X3 , X4, ΧΘ, Χβ, ΧΘ, Xio, X11 , X12 are independently from one other a carbon or a heteroatom, preferably a nitrogen atom, with the proviso that X ₄ and Xi are a nitrogen atom if X5 corresponds to a carbon atom in the form of a carbene.

[0067] R ^" and R ^'" , which may be the same or different at each occurrence, are hydrogen, halogen, NO ₂ , CN, NH ₂ , NHR ⁵¹ , N(R ⁵¹ ) ₂ , B(OH) ₂ , B(OR ⁵¹ ) ₂ , CHO, COOH, CONH2, CON(R ⁵¹ ) ₂ , CONHR ⁵¹ , SO ₃ H, C(=O)R ⁵¹ ,

P(=O)(R ⁵¹ ) ₂ , S(=O)R ⁵¹ , S(=O) ₂ R ⁵¹ , P(R ⁵¹ )s ⁺ , N(R ⁵¹ ) ₃ ⁺ , OH, OR ⁵¹ , SR ⁵¹ , Si(R ⁵¹ )3, a straight chain alkyl or alkoxy group having 1 to 20 carbon atoms or a branched or cyclic alkyl or alkoxy group with 3 to 20 carbon atoms, a haloalkyl group, a substituted or unsubstituted aromatic or heteroaromatic ring system having 5 to 50 ring atoms or a substituted or unsubstituted aryloxy, heteroaryloxy or heteroarylamino group having 5 to 50 ring atoms, two or more substituents R ^" and R ^'" , either on the same or on different rings may define a further mono- or polycyclic, aliphatic or aromatic ring system with one another or with a substituent R ⁵¹ ,

R ⁵¹ , which may be the same or different on each occurrence, may be hydrogen or a straight chain alkyl or alkoxy group having 1 to 20 carbon atoms or a branched or cyclic alkyl or alkoxy group with 3 to 20 carbon atoms, a substituted or unsubstituted aromatic or heteroaromatic ring system having 5 to 50 ring atoms or a substituted or unsubstituted aryloxy, heteroaryloxy or heteroarylamino group having 5 to 50 ring atoms, and a and b, independently from one another represent an integer in the range of from 0 to 3.

[0068] The two bidentate ligand units L ¹ and L ² , independently from each other, may be bound to arms B ¹ and B ² , if present, or to central scaffold A, through any position, including those from the R" and R'" substituents, or in any manner which does not interfere with those positions through which the bidentate ligand units are bound to the transition metal.

The bidentate ligand units corresponding to formulae (8) to (10) are preferably bound to arms B ¹ and B ² , if present, or to central scaffold A, through their 6-membered E1 and E2 rings via those atoms which are located in para position to the E1 -E2 bond (Xi-X6 bond), which correspond to X9 atom in formula (8), to X12 atom in formula (9) and to X9 and X12 atoms in formula (10). The bidentate ligand units L corresponding to formulae (8) to (10) are further preferably bound through their 6-membered E1 and E2 rings via the atom which is located in meta position to the E1 - E2 bond (Xi-X6 bond), which correspond to X10 atom in formula (8), to X3 atom in formula (9) and to X3 and X10 atoms in formula (10). Still another preferred linkage positions are those from 5-membered E1 and E2 rings corresponding to X3 and X ₄ atoms in formula (8) and to X9 atom in formula (9).

[0069] In accordance with another preferred embodiment at least one of

bidentate ligand units L ¹ and L ² is selected from the group consisting of phenylimidazole derivatives, phenylpyrazole derivatives, phenyltriazole derivatives, phenyltetrazole derivatives, 1 -phenyl-imidazol-2-ylidene derivatives, 2-(1 H-1 ,2,4-triazol-5-yl)pyridine derivatives, 2-(1 H-pyrazol-5- yl)pyridine derivatives, phenylpyridine derivatives, phenylquinoline derivatives and phenylisoquinoline derivatives.

In yet another preferred embodiment of the present invention, at least one of the L ¹ and L ² bidentate ligand units is selected from the group consisting of compounds of formulae (1 1 ) to (15) which pertain to general formula (8)

(13) (14) (15)

wherein R ¹⁶ and R ¹⁷ may be the same or different and are groups other than hydrogen, preferably selected from alkyl, haloalkyl, cycloalkyl, aryl and heteroaryl groups and more preferably from alkyl or haloalkyl groups and wherein R ¹⁸ to R ²⁰ may be the same or different and may be selected from the group consisting of hydrogen, halogen, NO2, CN, NH ₂ , NHR ²¹ , N(R ²¹ ) ₂ , B(OH) ₂ , B(OR ²¹ ) ₂ , CHO, COOH, CONH ₂ , CON(R ²¹ ) ₂ , CONHR ²¹ , SO3H, C(=O)R ²¹ , P(=O)(R ²¹ ) ₂ , S(=O)R ²¹ , S(=O) ₂ R ²¹ , P(R ²¹ ) ₃ ⁺ , N(R ²¹ ) ₃ ⁺ , OH, OR ²¹ , SR ²¹ , Si(R ²¹ ) ₃ and alkyl, haloalkyl, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl group, with R ²¹ being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups.

In accordance with yet another preferred embodiment, at least one of ligand units L ¹ and L ² is selected from the group consisting of compounds of formulae (16) to (26) which pertain to general formulae (1 1) and (12) (formulae 16 to 25) respectively to general formula (8) (formula 26)

(16) (17) (18)

(19) (20)

(21) (22) (23)

(24) (25) (26) wherein R ²² and R ²³ ' independent of one another, are selected from hydrogen halogen, NO ₂ , CN, NH ₂ , NHR ²⁴ , N(R ²⁴ ) ₂ , B(OH) ₂ , B(OR ²⁴ ) ₂ , CHO, COOH, CONH ₂ , CON(R ²⁴ ) ₂ , CONHR ²⁴ , SO ₃ H, C(=O)R ²⁴ ,

P(=O)(R ²⁴ ) ₂ , S(=O)R ²⁴ , S(=O) ₂ R ²⁴ , P(R ²⁴ ) ₃ ⁺ , N(R ² ) ₃ ⁺ , OH, OR ²⁴ , SR ²⁴ , Si(R ²⁴ ) ₃ and alkyl, haloalkyi, alkenyl, alkynyl, arylalkyi, aryl and heteroaryl group, with R ²⁴ being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups.

Still another preferred embodiment in accordance with the present invention is characterized by at least one of the L ¹ to L ² bidentate ligand units being selected from compounds of formulae (27) and (28) which pertain to general formula (8)

(27) (28)

wherein R ²⁵ to R ³² may be the same or different at each occurrence and may be selected from the group consisting of hydrogen, halogen, NO2, CN, NH2, NHR ³³ , N(R ³³ ) ₂ , B(OH) ₂ , B(OR ³³ ) ₂ , CHO, COOH, CONH ₂ , CON(R ³³ ) ₂ , CONHR ³³ , SO ₃ H, C(=O)R ³³ , P(=O)(R ³³ ) ₂ , S(=O)R ³³ ,

S(=O) ₂ R ³³ , P(R ³³ ) ₃ ⁺ , N(R ³³ ) ₃ ⁺ , OH, OR ³³ , SR ³³ , Si(R ³³ ) ₃ , and alkyl, haloalkyi, alkenyl, alkynyl, arylalkyi, aryl and heteroaryl groups, with R ³³ being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups. Further preferably, at least one of the L ¹ to L ² bidentate ligand units is selected from compounds of the general formulae (29) and (30) which pertain to general formula (9)

(29) (30) wherein R ³⁴ to R ³⁸ may be the same or different at each occurrence and may be selected from the group consisting of hydrogen, halogen, NO2, CN, NH2, NHR ³⁹ , N(R ³⁹ ) ₂ , B(OH) ₂ , B(OR ³⁹ ) ₂ , CHO, COOH, CONH ₂ , CON(R ³⁹ ) ₂ , CONHR ³⁹ , SO ₃ H, C(=O)R ³⁹ , P(=O)(R ³⁹ ) ₂ , S(=O)R ³⁹ ,

S(=O) ₂ R ³⁹ , P(R ³⁹ ) ₃ ⁺ , N(R ³⁹ ) ₃ ⁺ , OH, OR ³⁹ , SH, Si(R ³⁹ ) ₃ , and alkyl, haloalkyl, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl group, with R ³⁹ being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups.

[0074] In accordance with still another preferred embodiment, at least one of the L ¹ to L ² bidentate ligand units is selected from compounds of the general formulae (31 ) to (33) which pertain to general formula (10)

(31) (32) (33) wherein R ⁴⁰ to R ⁴⁹ may be the same or different at each occurrence and may be selected from the group consisting of hydrogen, halogen, NO ₂ , CN, NH ₂ , NHR ⁵⁰ , N(R ⁵⁰ ) ₂ , B(OH) ₂ , B(OR ⁵⁰ ) ₂ , CHO, COOH, CONH ₂ , CON(R ⁵⁰ ) ₂ , CONHR ⁵⁰ , SO ₃ H, C(=O)R ⁵⁰ , P(=O)(R ⁵⁰ ) ₂ , S(=O)R ⁵⁰ ,

S(=O) ₂ R ⁵⁰ , P(R ⁵⁰ ) ₃ ⁺ , N(R ⁵⁰ ) ₃ ⁺ , OH, OR ⁵⁰ , SR ⁵⁰ , Si(R ⁵⁰ ) ₃ and alkyl, haloalkyl, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl groups, with R ⁵⁰ being selected from hydrogen, alkyl, aralkyl, aryl and heteroaryl groups.

[0075] As explained above, the asymmetric tetradentate ligands forming part of the light emitting transition metal complexes in accordance with the present invention comprise at least one bidentate ligand unit L ¹ or L ² which is represented by formula (3) and (8) to (33) above and particularly preferred both ligand units L ¹ and L ² are represented by formulae (3) and (8) to (33).

[0076] The bidentate ligand units L ¹ and L ² are selected in such a way that the complexes comprising a subunit with a tetradentate ligand involving these two ligands units emit in the desired range. Without wishing to be bound to any theory, it is believed that the emission color of the complexes comprising a tetradentate ligand composed of two bidentate ligand units L ¹ and L ² will be mainly dictated in a first approximation by the bidentate ligand units L ¹ and L ² which has the lowest triplet energy or which leads to the homoleptic complex, respectively [M(L ¹ )3] and [M(L ² )3] , emitting at the lower energy, provided that the other ligand(s) needed to complete the coordination sphere do(es)n't contribute to the photoactive properties of the complex.

One the two bidentate ligand units L ¹ and L ² may also be selected in order to impart to the complexes higher solubility in most organic solvents without changing its emission color e.g by selecting a bidentate ligand unit L ² pertaining to the same family (phenylpyrazole, phenylimidazole...) as the ligand unit L ¹ .

[0077] Tetradentate ligands of formulae (L34) to (L40) are preferred ligands for subunits of the light emitting transition metal complexes of the present invention, wherein both L ¹ and L ² are selected from compounds of formulae (8) to (33). For the sake of simplicity A has been chosen to represent a benzene ring and B ¹ and B ² are CH2-CH2 units linked to A in meta positions to each other in each of formulae L34 to L40; it is also possible, however, to choose A and B ¹ and B ² as well as the way the pending arms B ¹ and B ² , if present, are linked to the central scaffold A from the broader definitions given hereinbefore. In the same way, for the sake of simplicity, it has been chosen to bind the pending arms B ¹ and B ² to the phenyl ring of the bidentate ligand units L ¹ and L ² in para position to the imidazole and/or pyrazole rings; it is also possible, however, to bind the bidentate ligand units L ¹ and L ² to pending arms B ¹ and B ² , if present, or to central scaffold A through any position or in any manner which does not interfere with those positions through which the bidentate ligand units L ¹ and L ² of the asymmetric tetradentate ligand are bound to the transition metal.

[0078] The subunit with the tetradentate ligands in accordance with the present invention may in another embodiment of the present invention comprise one ligand unit of formulae (3) and (8) to (33) and another bidentate ligand unit generally referred to in the prior art as "ancillary" ligands. In principle any ligand unit described in the prior art as bidentate ligand for transition metal complexes may be involved as "ancillary" ligand in the asymmetric tetradentate ligand in accordance with the present invention. Thus, reference may be made to the prior art documents describing such ligands. Just by way of example, acetylacetonate and picolinate ligand units may be mentioned here. The skilled person knows this type of ligand units which have been described in the literature.

[0079] The light emitting transition metal complexes in accordance with the

present invention comprise other ligands in addition to the tetradentate ligands which may be mono- or bidentate, preferably bidentate.

[0080] Preferred light emitting transition metal complexes in accordance with the present invention may be characterized by the general formulae 41

« '

[0081] wherein L' may be a bidentate ligand or a combination of two monodentate ligands, preferably a bidentate ligand and more preferably a bidentate

[0082] wherein

ΕΊ represents a nonmetallic atom group required to form a 5- or

6-membered aromatic or heteroaromatic ring, optionally condensed with additional aromatic moieties or non aromatic cycles, said ring optionally having one or more substituents, optionally forming a condensed structure with the ring comprising E'2, and

E'2 represents a nonmetallic atom group required to form a 5- or

6-membered aromatic or heteroaromatic ring, optionally condensed with additional aromatic moieties or non aromatic cycles, said ring optionally having one or more substituents, optionally forming a condensed structure with the ring comprising E'i, and

wherein the rings ΕΊ and E'2 could together form a polycyclic aliphatic, aromatic or heteroaromatic ring system and

wherein the ring ΕΊ is bound to the transition metal via a neutral donor atom which is a carbon in the form of a carbene or a heteroatom

preferably a nitrogen atom and the ring E'2 is bound to the transition metal through a carbon atom having formally a negative charge or through a nitrogen atom having formally a negative charge.

[0083] Preferred additional bidentate ligands L' in transition metal complexes of metals having a coordination number equal to six are ligands

corresponding to the bidentate ligand units described hereinbefore for the asymmetric tetradentate ligands. Such additional ligand L' may be identical to one of the ligand units L ¹ and L ² of the asymmetric tetravalent ligand or it may be different from either ligand unit L ¹ and L ² thus yielding transition metal complexes with three different bidentate ligand units coordinated to the metal.

[0084] Bidentate ligand L' may also be selected from ligands of general formulae E3-SBF, E3-Ar1 -SBF, E3-Open SBF and/or E3-Ar1 -Open SBF wherein E3 is a 5 -membered heteroaryl ring, bound to the metal atom by covalent or dative bonds and containing at least one donor nitrogen atom, wherein said heteroaryl ring may be un-substituted or substituted by substituents selected from the group consisting of halogen, alkyl, alkoxy, amino, cyano, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl group and/or may form an annealed ring system with other rings selected from cycloalkyl, aryl and heteroaryl rings;

Ar1 when present is bound to the metal atom by covalent or dative bonds and is selected from the group consisting of substituted or un-substituted C6-C30 arylene and substituted or un-substituted C2-C30 heteroarylene groups, which Ar1 group may be un-substituted or substituted by substituents selected from the group consisting of halogen, alkyl, alkoxy, amino, cyano, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl groups;

SBF represents 9,9'-spirobifluorenyl, Open SBF represents 9,9-diphenyl- 9H-fluorenyl, in both cases un-substituted or substituted by substituents selected from the group consisting of halogen, alkyl, alkoxy, amino, cyano, alkenyl, alkynyl, arylalkyl, aryl and heteroaryl groups.

[0085] The additional ligand L' may also be a bidentate ligand like picolinate, tetrakispyrazolylborate or acetylacetonate (generally referred to as ancillary ligands) or monodentate ligands as have been described in the literature as suitable for the manufacture of transition metal complexes.

[0086] In another preferred embodiment, the additional bidentate ligand L' is

selected in order to impart to the resulting complexes a higher solubility in most organic solvents.

[0087] The metal M in the light emitting transition metal complexes in accordance with the present invention represents a transition metal of atomic number of at least 40 and a coordination number equal to six, preferably Ir, Ru, Os, Re or Rh, most preferably Ir.

[0088] The light emitting materials in accordance with the present invention

generally have a number of advantageous properties. The increased bulkyness of the tetradentate ligands as compared to bidentate ligands often leads to a reduced T-T annihilation at high current densities as well as to a reduced aggregate-induced concentration quenching at high doping levels, which in turn leads to an increased device efficiency.

[0089] Because of their expected less labile ligand system, complexes involving tetradentate ligands in accordance with the present invention are believed to show improved chemical, thermal, electrochemical and photochemical stability as compared to their bidentate ligands analogs. Higher device lifetimes are thus expected.

[0090] Given their more rigid structure with decreased vibrational and rotational freedom, complexes comprising tetradentate ligands in accordance with the present invention are expected to show less efficient non-radiative decay pathways and thus increased photoluminescence quantum yields and higher devices efficiencies than their bidentate analogs.

[0091] The emission color from the complexes involving asymmetric tetradentate ligands in accordance with the present invention could be tuned over a large range of wavelengths according to the selected bidentate ligand units L ¹ and L ² and the selected additional ligand L'. Without wishing to be bound by theory, it is believed that the emission color of the heteroleptic complexes comprising the tetradentate ligand with bidentate ligand units L ¹ and L ² and the additional bidentate ligand L' will be mainly dictated in a first approximation by that of the bidentate ligands L ¹ , L ² or L' having the lowest triplet energy or leading to the homoleptic complex which emits at the lowest energy. So the "photoactive" ligand which is believed to contribute to the photoactive properties of the complexes comprising such ligands may be either the bidentate ligand unit L ¹ , the bidentate ligand unit L ² or the additional bidentate ligand L' according to the selection of the ligand units L ¹ and L ² and of the additional ligand L' which has been made. So, making the choice of the ligand units L ¹ and L ² and of the additional ligand L' in an appropriate way allows to select, on a very broad range of wavelengths, the emission color from the complexes involving asymmetric tetradentate ligands in accordance with the present invention.

[0092] So if one of the bidentate ligand units of the tetradentate ligand, e.g. L ¹ , is selected from the group consisting of compounds of formulae (1 1) to (26), blue emission would be expected provided L' and L ² are suitably selected from ligands having a triplet energy at least equal to that of bidentate ligand unit L ¹ corresponding to compounds of formula (1 1 ) to (26). In the same way, if the additional bidentate ligand L' is selected from the group consisting of compounds of formulae (1 1 ) to (26), blue emission would be expected provided L ¹ and L ² are suitably selected from ligands having a triplet energy at least equal to that of bidentate ligand L corresponding to compounds of formula (1 1 ) to (26). As mentioned before, especially blue- emitters need improvement in terms of lifetime and stability and the light- emitting materials in accordance with the present invention in preferred embodiments should provide significant advantages over the prior art in this regard as they should show a high efficiency while still providing a long lifetime.

[0093] More preferred blue emitting complexes in accordance with the present invention are those wherein both L ¹ and L ² bidentate ligand units of the asymmetric tetradentate ligand as well as the additional bidentate ligand L' pertain to general formula (1 1 ) and are thus represented by following general formula (42):

wherein A, B ¹ , B ² , q and r have the same meanings as in general formula (1 ) and wherein R ^16' , R ^16" , R ^16'" can have the same meanings as given for R ¹⁶ in formula (1 1 ), R ^17' , R ^17" , R ^17'" can have the same meanings as given for R ¹⁷ in formula (1 1 ), R ^18' , R ^18" , R ^18'" can have the same meanings as given for R ¹⁸ in formula (1 1 ), R ^19' , R ^19" , R ^19'" can have the same meanings as given for R ¹⁹ in formula (1 1 ) and R ^20' , R ^20" , R ^20'" can have the same meanings as given for R ²⁰ in formula (1 1 ) and with the proviso that at least one of the following conditions is observed: R ^16" is different from R ^16'" or R ^17" is different from R ^17'" or R ^18" is different from R ^18'" or R ^19" is different from R ^19'" or R ^20" is different from R ^20" . For the sake of simplicity it has been chosen in formula (42) to bind the pending arms B ¹ and B ² to the phenyl ring of the bidentate ligand units L ¹ and L ² in para position to the imidazole ring; it is also possible, however, to bind the bidentate ligand units L ¹ and L ² to pending arm B ¹ and B ² , if present, or to central scaffold A through any position or in any manner which does not interfere with those positions through which the bidentate ligand units L ¹ and L ² are bound to the transition metal. Blue emitting complexes in a still preferred embodiment in accordance with the present invention are selected from those corresponding to formulae (43), (43'), (44), (44'), (45), (45'), (46), (46'), (47) and (47') wherein all the different R groups have the same meaning as defined in formula (42) and obey to the same conditions as indicated for formula (42). For the sake of simplicity central scaffold A has been chosen to represent a benzene ring and B ¹ and B ² are CH2-CH2 units which are linked to A in meta positions to each other in formulae (43), (44), (45), (46) and (47) and in para positions to each other in formulae (43'), (44'), (45'), (46') and (47'); and it is also possible, however, to choose A, B ¹ and B ² from the broader definitions given hereinbefore as well as the way the pending arms B ¹ and B ² , if present, are linked to the central scaffold A as indicated

hereinbefore. Furthermore, for the sake of simplicity it has been chosen to bind the pending arms B ¹ and B ² to the phenyl ring of the bidentate ligand units L ¹ and L ² in para position to the imidazole ring in formulae (43), (44), (45), (46) and (47) and in meta position to the imidazole ring in formulae (43'), (44'), (45') (46') and (47'); it is also possible, however, to bind the bidentate ligand units L ¹ and L ² to pending arms B ¹ and B ² , if present, or to central scaffold A through any position or in any manner which does not interfere with those positions through which the bidentate ligand units L ¹ and L ² of the asymmetric tetradentate ligand are bound to the transition metal.

t6t/.90/£lOZd3/I3d osocco/Hoz OAV





[00107] In the same way, provided the right selection of the bidentate ligand units L ¹ and L ² and of the additional bidentate ligand L' has been made, green- emitting complexes are expected when at least one of these bidentate ligands L ¹ , L ² and L' is selected from formula (31 ) and orange/red ennitting complexes from bidentate ligands selected from formulae (32) and (33).

[00108] Because of expected reduced ligand scrambling when starting from a tetradentate ligand wherein two ligands units L ¹ and L ² are linked to one another, the syntheses of heteroleptic complexes (L ¹ ≠ L ² ≠ L') in accordance with the present invention are believed to lead to easier purification process and higher yield than synthesis starting from bidentate L ¹ , L ² and L' ligands, which would be highly valuable. Heteroleptic complexes are indeed of particular interest because their photophysical, thermal and electronic properties as well as their solubility can be tuned by selecting appropriate combination of ligands. Furthermore, they have been observed in some cases (e.g. US2010/0141 127A1) to yield better device lifetimes in OLEDs.

[00109] Given the very broad variety of bidentate ligand unit L ¹ and L ² and of

additional ligand L' which could be selected in the complexes involving asymmetric tetradentate ligands in accordance with the present invention, light-emitting materials combining high solubility in most organic solvents and desired emission properties, particularly in the blue region, are made available which is quite advantageous for low cost OLEDs production. It is indeed possible to properly select at least one of the bidentate ligand units L ¹ to L ² or the additional bidentate ligand L' in order to impart higher solubility to the light-emitting complexes without changing its emission wavelength.

[001 10] Another object of the invention is the use of the light emitting transition metal complexes as above described in the emitting layer of an organic light emitting device, e.g. a light emitting electrochemical cell (LEEC) or an organic light emitting diode (OLED).

[001 1 1] In particular, the present invention is directed to the use of the light

emitting transition metal complexes as above described as dopant in a host layer, functioning as an emissive layer in an organic light emitting device. [001 12] Should the light ennitting transition metal complexes be used as dopant in a host layer, they are generally used in an amount of at least 1 % wt, preferably of at least 3 % wt, more preferably of least 5 % wt with respect to the total weight of the host and the dopant and generally of at most 35 % wt, preferably at most 25 % wt, more preferably at most 15 % wt.

[001 13] The present invention is also directed to an organic light emitting device, in particular an organic light emitting diode (OLED) comprising an emissive layer (EML), said emissive layer comprising the light emitting transition metal complexes or mixture of same as above described, optionally with a host material (wherein the light emitting transition metal complexes as above described are preferably present as a dopant), said host material being notably suitable in an EML in an OLED.

[001 14] The present invention is also directed to light emitting electrochemical cells (LEEC) containing ionic complexes in accordance with the present invention.

[001 15] An OLED generally comprises :

a substrate, for example (but not limited to) glass, plastic, metal;

an anode, generally transparent anode, such as an indium-tin oxide (ITO) anode;

a hole injection layer (HIL) for example (but not limited to) PEDOT/PSS; a hole transporting layer (HTL);

an emissive layer (EML);

an electron transporting layer (ETL);

an electron injection layer (EIL) such as LiF, CS2CO3

a cathode, generally a metallic cathode, such as an Al layer.

[001 16] For a hole conducting emissive layer, one may have a hole blocking layer (HBL) that can also act as an exciton blocking layer between the emissive layer and the electron transporting layer. For an electron conducting emissive layer, one may have an electron blocking layer (EBL) that can also act as an exciton blocking layer between the emissive layer and the hole transporting layer. The emissive layer may be equal to the hole transporting layer (in which case the exciton blocking layer is near or at the anode) or to the electron transporting layer (in which case the exciton blocking layer is near or at the cathode).

[001 17] The ennissive layer may be formed with a host material in which the light emitting material or mixture of these materials as above described resides as a guest or the emissive layer may consist essentially of the light emitting material or mixture of these materials as above described itself. In the former case, the host material may e.g. be a hole-transporting material selected from the group of substituted tri-aryl amines. Preferably, the emissive layer is formed with a host material in which the light emitting material resides as a guest. The host material may be an electron- transporting material e.g. selected from the group of oxadiazoles, triazoles and ketones (e.g. Spirobifluoreneketones SBFK) or a hole transporting material. Examples of host materials are 4,4'-N,N'-dicarbazole-biphenyl ["CBP"] or 3,3'-N,N'-dicarbazole-biphenyl ["mCBP"] which have the formula :

[001 18]

mCPB

[001 19] Optionally, the emissive layer may also contain a polarization molecule, present as a dopant in said host material and having a dipole moment, that generally affects the wavelength of light emitted when said light emitting material as above described, used as dopant, luminesces.

[00120] A layer formed of an electron transporting material is advantageously used to transport electrons into the emissive layer comprising the light emitting transition metal complex and the (optional) host material. The electron transporting material may be an electron-transporting matrix selected from the group of metal quinoxolates (e.g. Alq3, Liq), oxadiazoles, triazoles and ketones (e.g. Spirobifluorene ketones SBFK). Examples of electron transporting materials are tris-(8-hydroxyquinoline)aluminum of formula ["Alq3"] and spirobifluoreneketone SBFK:

A layer formed of a hole transporting material is advantageously used to transport holes into the emissive layer comprising the light emitting material as above described and the (optional) host material. An example of a hole transporting material is 4,4'-bis[N-(1 -naphthyl)-N- phenylamino]biphenyl ["a-NPD"].

[00122] The use of an exciton blocking layer ("barrier layer") to confine excitons within the luminescent layer ("luminescent zone") is usually preferred. For a hole-transporting host, the blocking layer may be placed between the emissive layer and the electron transport layer. An example of a material for such a barrier layer is 2,9-dimethyl-4,7-diphenyl-1 ,10-phenanthroline (also called bathocuproine or "BCP"), which has the formula

[00123] The OLED has preferably a multilayer structure, as depicted in Figure 1 , wherein 1 is a glass substrate, 2 is an ITO layer, 3 is a HIL layer comprising e.g. PEDOT/PSS, 4 is a HTL layer comprising e.g. a-NPD, 5 is an EML comprising e.g. mCBP as host material and the light emitting material or mixture of these materials as above defined as dopant in an amount of about 15 % wt with respect to the total weight of host plus dopant; 6 is a HBL comprising e.g. BCP; 7 is an ETL comprising e.g. Alq3; 8 is an EIL comprising e.g.LiF and 9 is an Al layer cathode

[00124] The asymmetric tetradentate ligands forming part of the subunit of the light emitting transition metal complexes in accordance with the present invention may be obtained by a number of processes which have been principally described in the literature and are known to the skilled person.

[00125] By way of example a stepwise Sonogashira coupling reaction may be

mentioned here.

[00126] The Sonogashira coupling reaction is a cross coupling reaction used

widely in organic synthesis to form carbon-carbon bonds between a terminal alkyne group and an aryl or vinyl halide using a palladium based catalyst. The reaction has the advantage that it can be carried out under mild conditions, e.g. at room temperature and/or in aqueous media and with mild bases which is advantageous to avoid or suppress side reactions which may occur otherwise.

[00127] In principle the starting materials of the reaction may be a compound A- (B ¹ )-L ¹ with a terminal ethynyl group which is reacted with a compound L ² bearing a halide group or starting with a compound A-(B ¹ )-L ¹ with a halide group which is reacted with a compound L ² bearing a terminal ethynyl group. Respective starting materials may be obtained in accordance with methods known to the skilled person or are available commercially form certain suppliers.

[00128] Another possibility to obtain the asymmetric tetradentate ligands present in the complexes of the present invention is the so called Suzuki-Myaura coupling, according to which phenylboronic acid treacts with haloarenes. The reaction proceeds smoothly in the presence of bases with good yields. The principle reaction scheme for coupling two phenyl units may be depicted as follows:

[00130] The reaction proceeds smoothly and under mild conditions with palladium compounds, e.g. tetrakis (triphenylphosphine)palladium, Pd(PPh3)4, as catalyst in the presence of bases like sodium hydroxide or sodium carbonate as bases. In some cases weak bases like sodium carbonate have proved to be advantageous over strong bases like NaOH.

[00131] Instead of the bromides, the respective iodides are also suitable reactants whereas the respective chlorides are usually inert under the reaction conditions.

[00132] Furthermore, the phenyl group in the above reaction scheme may be

substituted or unsubstituted and the phenyl ring may be replaced by other aromatic or heteroaromatic ring systems to obtain a wide variety of compounds. [00133] It is easily recognizable that subsequent repetition of this reaction can provide the desired asymmetric tetradentate ligands.

[00134] Further details concerning the Suzuki-Myaura coupling and suitable

reaction conditions can be taken from Suzuki et al., Synth. Comm. 1 1 (7),

513-519 (1981 ).

[00135] Still another possibility to obtain the asymmetric tetradentate ligands may be the arylation of primary or secondary amines with e.g. biphenyl compounds according to the following principal reaction scheme

[00136] Similar to the Suzuki-Myura coupling the reaction can be repeatedly

applied to obtain the desired compounds. Further details concerning reaction conditions can be taken from Angew. Chem. Int. Ed. 42, 2051 - 2053 (2003) to which reference is made in this regard. Similar to the Suzuki-Myaura coupling this reaction is a versatile tool and can be applied to a broad range of starting materials.

[00137] It is also possible to combine the two aforementioned reactions in two subsequent steps to obtain desired tetradentate ligands. This may be generally depicted as follows:

[00139] The skilled person will easily recognize that the upper route uses the

Suzuki-Myaura coupling first followed by the amine arylation whereas the lower route uses the amine arylation first followed by a Suzuki-Myaura coupling.

[00140] In the above general reaction scheme, the aryl rings may carry

substituents or may be unsubstituted.

[00141] The reaction conditions will be selected by the skilled person based on his professional knowledge and the information available for reactions of this type.

[00142] The light emitting transition metal complexes comprising asymmetric

tetradentate ligands in accordance with the present invention may be prepared using known methods described in the prior art .

[00143] A first preferred process to synthesize the light emitting transition metal complexes in accordance with the present invention which comprise an asymmetric tetradentate ligand and an additional bidentate ligand L' comprises reacting the halo-bridged dimer complex of general formula [Ι_'2Μ(μ-Χ)2ΜΙ_'2] comprising the additional bidendate ligand L' and bridging halide ligand X ^" with the desired asymmetric tetradentate ligand in a solvent mixture of an organic solvent and water comprising more than 25 vol% of water, based on the volume of the overall solvent mixture, at a temperature of from 50 to 260 °C, optionally in the presence of from 0 to 5 molar equivalents, relative to the number of moles of halide X ^" ion introduced into the reaction mixture through the halo-bridged dimer, of a scavenger for halide X ^" ion and of from 0 to 10 vol%, based on the total volume of the solvent mixture, of a solubilisation agent increasing the solubility of the halo-bridged dimer in the reaction mixture.

[00144] The halo-bridged dimer complex of general formula [Ι_'2Μ(μ-Χ)2ΜΙ_'2] which comprises the additional bidentate ligand L' can be obtained according to known processes described in the literature, e.g. by reaction of the respective metal halides and/or their hydrates with additional bidentate ligand L'. Most preferred halides are chlorides and bromides. For example, in the case of iridium metal, a well-known procedure to synthesize the chloro-bridged dimer [L'2lr( -CI)2lrL'2] consists to react IrCb.xH O with a slight excess of the bidentate ligand L' (2.5 to 3 mol/mol Ir) in a 3: 1 (v/v) mixture of 2-ethoxyethanol and water at reflux for ¾ 20 h.

[00145] In accordance with this preferred process, the reaction of the halo bridged dimer [Ι_'2Μ(μ-Χ)2ΜΙ_'2] with the desired tetradentate ligand is carried out in a mixture of an organic solvent and water, which mixture comprises more than 25 vol% of water. The mixture preferably contains not more than 70 vol.% of an organic solvent and at least 30 vol.% of water.

[00146] According to this preferred process, the reaction is carried out in a solvent mixture comprising an organic solvent and water, preferably in a

homogeneous solution. The term "homogeneous solution" used herein relates to the solvent mixture. Preferably, the organic solvent may be at least one selected from a group consisting of Ci~C2o alcohols, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol or tert-butanol, oxanes, for example, dioxane or trioxane, Ci~C2o alkoxyalkyl ethers, for example, bis(2-methoxyethyl) ether, Ci~C2o dialkyl ethers, for example, dimethyl ether, Ci~C2o alkoxy alcohols, for example, methoxyethanol or ethoxyethanol, diols or polyalcohols, for example, ethylene glycol, propylene glycol, triethylene glycol or glycerol, polyethylene glycol, or dimethyl sulfoxide (DMSO), N-methyl pyrrolidone (NMP) or dimethyl formamide (DMF), and combinations thereof. More preferably, the organic solvent may be at least one selected from a group consisting of dioxane, trioxane, bis(2-methoxyethyl) ether, 2-ethoxyethanol and combinations thereof. Most preferably, the organic solvent is dioxane or bis(2-methoxyethyl) ether (hereinafter referred to as diglyme)

[00147] The reaction temperature is generally in the range of from 50 to 260 °C, preferably in the range of from 80 to 150 °C. In some specific

embodiments, the process is carried out at a pressure of from 1 χ 10 ³ to 1 x 10 ⁸ Pa, preferably 1 χ 10 ⁴ to 1 χ 10 ⁷ Pa, and most preferably 1 χ 10 ⁵ to 1 x 10 ⁶ Pa.

[00148] The tetradentate asymmetric ligand is preferably used in a stoichiometric amount relative to the amount of metal in the halo-bridged dimer or in a molar excess relative to the amount of metal in the halo-bridged dimer. In a more specific embodiment, the ligand compound is used in an amount of 10 to 3000 mol percent excess, preferably 50 to 1000 mol percent excess, most preferably 100 to 800 mol percent excess.

[00149] This process can be carried out in the presence or in the absence of a scavenger for halide ion X-. If halide ion scavenger is present, it is used in amount of up to 5, preferably up to 3 moles per mole of halide X ^" ion introduced into the reaction mixture through the halo-bridged dimer.

Preferred scavengers are silver salts. Most preferred silver salts are tetrafluoroborate, trifluoroacetate or triflate.

[00150] In certain cases, where the solubility of the halo-bridged dimer in the

solvent mixture is very low, it has proven to be advantageous to add up to 10 vol%, preferably of from 0.1 to 10 vol%, even more preferably of from 0.5 to 5 vol%, based on the volume of the solvent mixture, of a solubilising agent to improve the solubility of the dimer in the reaction solvent. DMSO has shown to work particularly well as solubilizing agent in certain cases.

[00151] Given that proton ions, hbO ^"1" , produced during the reaction may have an inhibitory effect, a neutralization step could be preferably carried out during the reaction in order to improve the complex yields.

[00152] In one embodiment of this process the halo-bridged dimer complex of general formula [Ι_'2Μ(μ-Χ)2ΜΙ_'2] comprising the additional bidentate ligand L' can be treated in a 1 ^st step with a scavenger for halide ion (most preferred scavenger being silver salt, silver triflate e.g.) in an organic solvent, e.g. a Ch C /MeOH mixture or ethanol and the intermediate complex obtained after filtration and removal of solvents can be reacted in a 2 ^nd step with the desired asymmetric tetradentate ligand at a

temperature of from 50 to 260 °C in a solvent mixture of an organic solvent and water comprising more than 25 vol% of water.

[00153] In another embodiment of this process, the precursor complex obtained by reaction of the desired tetradentate asymmetric ligand with metal halides and/or their hydrates, which could be considered as a halo-bridged dimer complex, can be reacted with the desired additional bidentate ligand L' in a solvent mixture of an organic solvent and water comprising more than 25 vol% of water, based on the volume of the overall solvent mixture, at a temperature of from 50 to 260 °C, optionally in the presence of from 0 to 5 molar equivalents, relative to the number of moles of halide X ^" ion introduced into the reaction mixture through the halo-bridged dimer, of a scavenger for halide X ^" ion and of from 0 to 10 vol%, based on the total volume of the solvent mixture, of a solubilisation agent increasing the solubility of the halo-bridged dimer in the reaction mixture. For example, this precursor complex in the case of iridium metal could be obtained by reacting IrCb.xH O with a stoichiometric or a slight excess amount of the desired tetradentate ligand (1.0 to 3.0 mol/mol Ir) in a 3: 1 (v/v) mixture of 2-ethoxyethanol and water at reflux for ¾ 20 h.

[00154] The precursor complex obtained by reaction of the desired tetradentate asymmetric ligand with the selected metal halides could also be used as starting material in other synthesis routes to the light-emitting transition metal complexes in accordance with this invention.

[00155] Such precursor could e.g. be treated directly with the bidentate additional ligand L' in an organic solvent at a temperature in the range of from 40°C to 260 °C.

[00156] Alternatively the same precursor can be treated in a first step with a

scavenger for halide ions in an organic solvent, e.g a

methanol/dichloromethane mixture, ethanol or acetone, and the

intermediate complex obtained after filtration and removal of the solvent can then be treated in a second step with the additional bidentate ligand L' in an organic solvent at a temperature in the range of from 40°C to 260 °C.

[00157] A one-pot variant of this synthesis can also be used. In that case the

precursor is reacted with the additional bidentate ligand L' in presence of a scavenger for halide ion in an organic solvent at a temperature in the range of from 40°C to 260 °C.

[00158] The reaction with the additional bidentate ligand L' in these three last

cases could be performed in presence of an organic or inorganic base in order to increase the yield.

[00159] Preferably, the organic solvent used to perform the reaction with the

additional bidentate ligand L' in these three last synthesis routes may be at least one selected from a group consisting of chlorinated solvents, for example CH2CI2, Ci~C2o alcohols, for example, methanol, ethanol, n- propanol, isopropanol, n-butanol, isobutanol or tert-butanol, oxanes, for example, dioxane or trioxane, Ci~C2o alkoxyalkyl ethers, for example, bis(2-methoxyethyl) ether, Ci~C2o dialkyl ethers, for example, dimethyl ether, Ci~C2o alkoxy alcohols, for example, methoxyethanol or

ethoxyethanol, diols or polyalcohols, for example, ethylene glycol, propylene glycol, triethylene glycol or glycerol, polyethylene glycol, Ci~C2o ketones, for example acetone, butanone, or dimethyl sulfoxide (DMSO), N- methyl pyrrolidone (NMP), acetonitrile or dimethyl formamide (DMF), and combinations thereof.

[00160] A three-step synthesis analogous to that described in JP2008/303150 for the synthesis of homoleptic complexes comprising 2-phenylimidazole type ligands which starts from IrC and passes successively by the chloro- bridged dimer and the heteroleptic acac complex to finally obtain the tris homoleptic complexes could also be used. In this case, the dimer precursor obtained from the reaction of the desired tetradentate

asymmetric ligand with the selected metal halides (MX3.XH2O) could be reacted with acetylacetonate type ligands in presence of a base (e.g. Na2CO3) in an organic solvent, e.g. 2-ethoxyethanol, to lead to a heteroleptic complex comprising the asymmetric tetradentate ligand as the main ligand and acetylacetonate as ancillary bidentate ligand. In a last step the heteroleptic complex comprising the acetylacetonate as ancillary can then be reacted with an additional bidentate ligand L' to give the heteroleptic complexes comprising the desired asymmetric tetradentate ligand and the desired additional bidentate ligand L'.

[00161] Metal acetylacetonate complexes (e.g. (Ir(acac)3) could also be used as starting materials. It has been shown that light emitting transition metal complexes comprising asymmetric tetradentate ligands in accordance with the present invention could be obtained e.g by treating lr(acac)3) with a mixture of the desired tetradentate asymmetric ligand and the selected additional bidentate ligand L' at high temperatures (e.g. > 200 °C) without any added solvent.

[00162] When the additional bidentate L' ligand corresponds to a C ^A C ligand which is bound to the metal via a neutral donor atom which is a carbon in the form of a carbene and through a carbon atom having formally a negative charge, a carbene precursor complex involving the additional bidentate ligand L' could be first prepared which can then be allowed to react in a second step with the tetradentate ligand in presence of a silver salt. In the case of iridium e.g, this carbene precursor can be an iridium (I) complex e.g. [lr(COD)(L')CI] wherein COD corresponds to a 1 ,5-cyclooctadiene ligand and wherein L' is linked to the iridium (I) ion via its carbene part.

[00163] The light-emitting transition metal complexes in accordance with the

present invention may be purified by recrystallization, column

chromatography or sublimation to name only a few possibilities

[00164] The skilled person will use his professional knowledge to select the

suitable reactants and reaction conditions based on the specific

combination of tetradentate and bidentate or monodentate ligands. [00165] Other synthesis methods are suitable and are known to the skilled person so that no further details are necessary here.

[00166] The light emitting transition metal complexes in accordance with the

present invention provide the possibility to precisely adjust and modify the properties by selection of the bidentate ligand units L ¹ and L ² and of the additional bidentate ligand L' in accordance with the specific application case.

[00167] Thereby the emission properties of organic electronic devices comprising the light emitting materials in accordance with the present invention can be finely tuned and adjusted to the specific application.

[00168] Examples

[00169] 1°) Synthesis of complexes wherein L ¹ * L ² * L' and wherein both the

bidentate ligand units L ¹ and L ² of the asymmetric tetradentate ligand as well as the additional bidentate ligand L' are cyclometallated C ^A N ligands bound to the iridium metal via a neutral donor nitrogen atom and through a carbon atom having formally a negative charge

[00170] Example 1 : Synthesis of complex I (formula below) wherein one bidentate ligand unit, e.g. L ¹ of the asymmetric tetradentate ligand pertains to general formula (10) and the other bidentate ligand unit L ² of the asymmetric tetradentate pertains to general formula (8) while the additional bidentate ligand L' pertains to general formula (8). More specifically the asymmetric tetradentate ligand corresponds to ligand L48 (as defined hereinafter) wherein the bidentate ligand unit L ¹ pertains to general formula (31 ) and the bidentate ligand unit L ² pertains to general formula (8) while the additional bidentate ligand L' pertain to general formula (1 1 ) and more particularly to formula (17).

[00171]

[00173] a) Synthesis of asymmetric tetradentate ligand L48

[00174] The bidentate ligand unit L ¹ pertains to general formula (31 ) and the

bidentate ligand unit L ² pertains to general formula (8); the central scaffold A is a phenyl ring and both pending arms B ¹ and B ² are -CH2-CH2- units linked in para position to each other on the A phenyl ring.

[00175] Ligand L48 was synthesized according to the following scheme:

[00177] Synthesis of 4-(4-iodophenethyl)-2-(4-(trifluoromethyl)phenyl)pyridine intermediate (1)

1 ^st step: A two-neck flask was filled with 120 ml_ of THF and 20 ml_ of a 2 M K2CO3 solution. Nitrogen was bubbled through the solvent mixture. 0.788 ml_ of 2-bromo-4-methylpyridine (7.1 mmol) and 1.62 g of 4- (trifluoromethyl)phenylboronic acid (8.5 mmol) were then added. After bubbling nitrogen for another ten minutes, 0.4 g of

tetrakis(triphenylphosphino)palladium(0) (0.34 mmol) were added and the reaction mixture was refluxed under nitrogen overnight. After letting it cool down to room temperature, the mixture was extracted between CH2CI2 and water. The combined organic phases were dried over MgSO ₄ and filtered. The solvent was removed leading to a yellow oil. The crude product was purified by column chromatography (S1O2 ;

Hexane/Ethylacetate, 7:3) leading to 1.1 g of the desired product as a white solid, as confirmed by 1 H-NMR and electrospray ionization mass spectrometry.

m/z (ESI-MS+) found 238.0840 ([M+H] ⁺ ), 260.0655 ([M+Na] ⁺ ).

[00178] 2 ^nd step: 1.05 g (4.4 mmol) of 4-methyl-2-(4-

(trifluoromethyl)phenyl)pyridine from 1 ^st step were placed in a flame dried Schlenk flask. It was evacuated and refilled with nitrogen three times. Dry THF (15 ml_) was added and the flask was placed in an ice bath. 2.95 ml_ (4.4 mmol) of a 1.5 M solution of lithium diisopropylamide were added dropwise. The solution was stirred at this temperature for 1.5 h. A solution of 1.31 g (4.4 mmol) of 4-iodobenzyl bromide in 10 mL THF was prepared in a second flask under nitrogen. It was then added dropwise to the first solution and the mixture was stirred at ambient temperature over night. Water was then added to quench the reaction. After extraction between ethylacetate and water the organic layer was dried over MgSO4 and filtered. After removal of the solvent the crude compound was purified by column chromatography on S1O2 with hexane/EtOAc 7:3 to get the desired product as a white solid, as confirmed by 1 H-NMR and electrospray ionization mass spectrometry. Yield: 0.34 g m/z (ESI-MS+) calcd 454.0274 ([M+H] ⁺ ) found 454.0267

1H NMR (300 MHz, CDCIs) δ 8.55 (s, 1 H), 7.97 (s, 2H), 7.69 (s, 2H), 7.55 (d, J = 8.3 Hz, 2H), 7.39 (s, 1 H), 7.05 (s, 1 H), 6.84 (d, J = 8.2 Hz, 2H), 2.88 (d, J = 3.8 Hz, 4H).

[00179] Synthesis of 5-(3-ethynylphenyl)-1-methyl-3-propyl-1 H-1 ,2,4-triazole

intermediate (2)

[00180] 2.23 g (15.3 mmol) of 3-ethynylbenzoic acid were suspended in 50 ml_ of dichloromethane. 5.2 ml_ (61 mmol) of oxalyl chloride were added followed by the addition of 3 drops of dry DMF. The reaction mixture was stirred at room temperature until all solids had dissolved, indicating complete conversion to the acid chloride. The solvent and excess oxalyl chloride were removed in vacuo and the resulting solid used immediately without further purification.

It was redissolved in 50 ml_ of CH2CI2 and 2.31 g (15.3 mmol) of

ethylbutyrimidate hydrochloride were added. A solution of 4.22 ml_ (30.5 mmol) of triethylamine in 10 mL of CH2CI2 was added dropwise and the resulting mixture was stirred at room temperature over night. The solution was washed with water (3 x 50 mL). After drying over MgSO ₄ the mixture was filtered into a round bottom flask.

0.8 mL (15.3 mmol) of methylhydrazine were added and the reaction mixture was stirred at room temperature over night. The next day it was again washed with water, dried over MgSO ₄ and filtered. The solvent was removed under vacuum to yield the crude product as a yellow oil. It was purified by column chromatography on S1O2 with Hex/EtOAc 7:3 yielding a white solid in 70 % yield as confirmed by 1 H-NMR and electrospray ionization mass spectrometry.

¹ H NMR (300 MHz, CDC13) δ 7.75 - 7.68 (m, 1 H), 7.62 - 7.55 (m, 1 H), 7.52 (dt, J = 7.7, 1.3 Hz, 1 H), 7.39 (t, J = 7.8 Hz, 1 H), 3.86 (s, 3H), 3.07 (s, 1 H), 2.79 - 2.52 (m, 2H), 1.74 (dd, J = 15.1 , 7.5 Hz, 2H), 0.94 (t, J = 7.4 Hz, 3H).

m/z (ESI-MS+) calcd. 226.1339 ([M+M ⁺ ) found 226.1342 [00181 ] Synthesis of 4-(4-((3-(1 -methyl-3-propyl-1 H-1 ,2,4-triazol-5- yl)phenyl)ethynyl)phenethyl)-2-(4-(trifluoromethyl)phenyl)py ridine (3)

[00182] A round bottonn flask was charged with 0.67 g (3 mmol) of compound (2) and 1.34 g (3 mmol) of compound (1). A 1 : 1 mixture of NEt ₃ and THF (30 ml_) was used as a solvent. Nitrogen was bubbled through the solution for 10 min. 63 mg (0.09 mmol) of PdCI ₂ (PPh ₃ )2 and 30 mg (0.15 mmol) of Cul were added and the reaction mixture was heated to 65 °C over night. After letting the solution cool down to room temperature the mixture was extracted between ethylacetate and water. The organic phase was dried over MgSO ₄ , filtered and the solvent removed. The crude compound was purified by column chromatography on S1O2 with hexane/EtOAc 7:3 to get the desired product as a light yellow solid, as confirmed by 1 H-NMR and electrospray ionization mass spectrometry. Yield: 0.64 g

1H-NMR (CDCIs): δ = 8.45 (d, 1 H), 7.90 (d, 2 H), 7.69 (s, 1 H), 7.59 (d, 2 H), 7.50 (d, 2 H), 7.34 (m, 4 H), 6.95 (m, 3 H), 3.81 (s, 3 H), 2.88 (s, 3 H), 2.56 (t, 2 H), 1.66 (m, 2 H), 0.83 (t, 4 H);

m/z (ESI-MS+) calcd 551.2417 ([M+H] ⁺ ) found 551.241 1 ,

[00183] Synthesis of asymmetric tetradentate ligand L48

[00184] 0.4 g of compound (3) were placed in a thick-wall Schlenk flask. Methanol was added. It was degassed with three cycles of evacuation and refilling with nitrogen. A scoop of palladium on activated carbon (10 wt % loading) was added. The reaction mixture was degassed again three times. The flask was then set under a pressure of 1.5 bar of hydrogen gas and the mixture was stirred at ambient temperature for two days. Remained hydrogen was washed out with a stream of nitrogen. The black mixture was filtered through celite (diatomaceous earth) to get the pure product as a clear colorless oil in quantitative yield as confirmed by 1 H-NMR and electrospray ionization mass spectrometry

¹ H NMR (300 MHz, CDCIs) δ 8.51 (d, J = 4.9 Hz, 1 H), 7.94 (t, J = 16.8 Hz, 2H), 7.62 (d, J = 8.2 Hz, 2H), 7.39 (t, J = 8.0 Hz, 3H), 7.30 (t, J = 7.5 Hz, 1 H), 7.25 - 7.1 1 (m, 1 H), 7.10 - 6.83 (m, 5H), 3.76 (s, 3H), 3.16 - 2.74 (m, 8H), 2.66 (dd, J = 18.3, 10.8 Hz, 2H), 1.83 - 1.62 (m, 2H), 0.93 (t, J = 7.4 Hz, 3H).

m/z (ESI-MS+) calcd. 555.2730 ([M+H] ⁺ ) found 555.2729

[00185] b) Synthesis of complex I wherein the additional bidentate ligand L'

correspond to formula (8) and more specifically to formula (17)

[00186]

[00187] 1.3 g (2.34 mmol) of ligand L48 and 0.81 g (2.34 mmol) of lrCI ₃ .xH ₂ O were heated to 120 °C in 2-ethoxyethanol under nitrogen over night. After cooling to room temperature, an excess of water was added to induce precipitation of the yellow product. It was filtered on a glass-frit and air- dried to get 1.37 g of a yellow powder. This powder was used without further purification.

[00188] 0.1 g (0.064 mmol) of this dimer precursor and 78 mg (0.26 mmol) of 1 - (2,6-diisopropylphenyl)-2-phenyl-1 H-imidazole additional ligand Ι_Ί were dissolved in ethylene glycol. Nitrogen was bubbled through the solution. 85 mg (0.38 mmol) of silver trifluoroacetate was added and the mixture was then heated in the dark to 190 °C over night. After cooling to room temperature, it was extracted between CH2CI2 and water. The organic phase was dried over MgSO ₄ , filtered and the solvent removed. The crude product was purified twice by column chromatography on silica gel, using Ch C /MeOH 5% leading to the desired complex as confirmed by ¹ H- NMR and MALDI-TOF mass spectrometry.

[00189] max of emission (nm) in CHCh solution at room temperature: 525 (max), 551 sh [00190] 2°) Synthesis of complexes wherein L ¹ * L ² * L' and wherein both the bidentate ligand units L ¹ and L ² of the asymmetric tetradentate ligand are cyclometallated C ^A N ligands while the additional bidentate ligand L' is a N ^A N ligand which is bound to the iridium metal via a neutral donor nitrogen atom and through a nitrogen atom having formally a negative charge

[00191] Example 2: Synthesis of complex II (formula hereafter) wherein one

bidentate ligand unit, e.g. L ¹ of the asymmetric tetradentate ligand pertains to general formula (10) and the other bidentate ligand unit L ² of the asymmetric tetradentate pertains to general formula (8) while the additional bidentate Ν ^Λ Ν ligand L' pertains to general formula (9). More specifically the asymmetric tetradentate ligand corresponds to ligand L48 (from example 1 ) wherein the bidentate ligand unit L ¹ pertains to general formula (31 ) and the bidentate ligand unit L ² pertains to general formula (8) while the additional bidentate ligand L' pertains to general formula (9) and more particularly to formula (29).

[00192]

[00193] Example 3: Synthesis of complex III (formula hereafter) wherein one

bidentate ligand unit, e.g. L ¹ of the asymmetric tetradentate ligand pertains to general formula (10) and the other bidentate ligand unit L ² of the asymmetric tetradentate ligand pertains to general formula (8) while the additional bidentate Ν ^Λ Ν ligand L' pertains to general formula (9). More specifically the asymmetric tetradentate ligand corresponds to ligand L48 (from example 1 ) wherein the bidentate ligand unit L ¹ pertains to general formula (31 ) and the bidentate ligand unit L ² pertains to general formula (8) while the additional bidentate ligand L' pertains to general formula (9) and more particularly to formula (30).

[00194] Complex III

[00195] The same synthesis procedure has been used for complex II and complex III.

[00196] 1 ^st step: Dichloro-bridged dimer precursor synthesis from tetradentate li nd L48 and lrCI ₃ .xH ₂ O

[00197]

[00198] 160 mL of a 2-ethoxyethanol/water 3: 1 v/v mixture were placed in a 2-neck flask and nitrogen was bubbled through the solution. 0.2 g (0.36 mmol) of tetradentate ligand L48 was dissolved in 10 mL of hot 2-ethoxyethanol and added to the vigorously stirred solution. After additional 10 min of nitrogen bubbling, 0.13 g (0.36 mmol) of IrCb.xH O was added and the resulting mixture was heated to 120 ^° C over night. After cooling to room

temperature, the mixture was poured into an excess of ice-cold water. The formed precipitate was filtered on a glass-frit and air-dried to get 0.19 g of a yellow powder. It was used for the next step without further purification.

[00199] 2 ^nd step: reaction of the dimer precursor with selected additional ligand L' [00200] 1 eq. of dimer precursor was dissolved in CH2CI2 and treated with 2 eq. of silver trifluoromethanesulfonate. It was stirred at room temperature over night in the dark. After filtering through celite, 2.2 eq of the additional bidentate Ν ^Λ Ν ligand L' and 2.2 eq of triethylamine were added. The resulting mixture was heated to 50 °C over night. After filtering and removal of the solvent, the complexes were purified by column

chromatography on silica gel, using Ch C /MeOH as eluent (gradient of 1 % to 5%).

[00201] Complex II: yield: 43 mg when starting from 280 mg of dimer-precursor.

[00202] ¹ H NMR(300 MHz CDCI3) δ 8.75 - 5.51 (m, 17H), 4.37 - 3.60 (m, 2H), 3.35 - 2.31 (m, 5H), 2.0 - 0.28 (m, 20H),

MS-ESI: m/z : calcd. 947.3346 [M+H ⁺ ], found 947.3353

max emission (nm) in CH2CI2 at room temperature = 516

[00203] Complex III: yield: 16 mg when starting from 80 mg of dimer-precursor

[00204] ¹ H NMR(400 MHz CD2CI2) δ 7.92 - 6.45 (m, 17H), 4.41 - 3.77 (m, 3H), 3.20 - 2.69 (m, 8H), 2.06 - 1.14 (m, 15H) 1.03 (dd, J=8.4, 6.5 Hz, 1 H), MS-MALDI: m/z : calcd. 1014.326 [M+H ⁺ ], found 1014.241

max emission (nm) in CH2CI2 at room temperature: 502 (max), 527 _S h

[00205] 3°) Synthesis of complexes wherein L ¹ * L ² * L' and wherein both the

bidentate ligand units L ¹ and L ² of the asymmetric tetradentate ligand are cyclometallated C ^A N ligands while the additional bidentate ligand L' is a C C ligand which means that it is bound to the iridium metal via a neutral donor atom which is a carbon in the form of a carbene and through a carbon atom having formally a negative charge.

[00206] Example 4: Synthesis of complex IV (formula hereafter) wherein both the bidentate ligand units L ¹ and L ² of the asymmetric tetradentate ligand as well as the additional bidentate C ^A C ligand L' pertain to general formula (8). More specifically the asymmetric tetradentate ligand corresponds to ligand L49 (formula hereafter) wherein the bidentate ligand unit L ¹ pertains to general formula (1 1 ) and more particularly to formula (16) and the bidentate ligand unit L ² pertains to general formula (8) while the additional bidentate C ^A C ligand L' pertains to general formula (28).

[00207] Complex IV

[00208] a) Synthesis of asymmetric tetradentate ligand L49

[00209] The bidentate ligand unit L ¹ pertains to general formula (1 1 ) and more particularly to formula (16) and the bidentate ligand unit L ² pertains to general formula (8); the central scaffold A is a phenyl ring and both pending arms B ¹ and B ² are -CH2-CH2- units linked in para position to each other on the A phenyl ring.

[00210] The ligand L49 was synthesized according to the following scheme:

[0021 1]

[00212] Synthesis of 5-(3-((4-iodophenyl)ethynyl)phenyl)-1 -methyl-3-propyl-1 H- 1 ,2,4-triazole intermediate (4)

[00213] 2 g (8.9 mmol) of intermediate (2) from example 1 and 5.87 g (17.8 mmol) of 1 ,4-diiodobenzene were dissolved in 200 ml_ of a 1 : 1 mixture of THF and NEt.3. Nitrogen was bubbled through the solution for 10 min. 0.31 g (0.44 mmol) of PdCI ₂ (PPh ₃ )2 was then added followed by addition of 0.17 g (0.89 mmol) of Cul. The reaction mixture was stirred at 65 °C over night. After cooling to room temperature, 100 ml_ of CH2CI2 were added and it was washed with cone. NH ₄ OH three times to remove the copper catalyst. After two washings with water, the organic layer was dried over MgSO ₄ . After filtration and removal of the solvent, the crude mixture was purified by column chromatography on silica gel with hexane/ethyl acetate

(Hex/EtOAc) 1 : 1 leading to 2.2 g of the desired product as confirmed by 1H-NMR. [00214] Synthesis of 1 -(2,6-dimethylphenyl)-2-(3-ethynylphenyl)-1 H-imidazole intermediate (5)

[00215] 5 g (15.3 mmol, 1 eq.) of 2-(3-bromophenyl)-1-(2,6-dimethylphenyl)-1 H- imidazole were dissolved in dry toluene. 6.6 ml_ (22.9 mmol, 1.5 eq.) of tributyl(ethynyl)stannane were added and nitrogen was bubbled through the solution for 10 min. After the addition of 0.9 g (0.76 mmol, 0.05 eq) of tetrakis(triphenylphosphine)palladium(0) the bubbling was continued for another 10 min. The reaction mixture was heated to reflux over night. The solution was allowed to cool to room temperature and EtOAc and water were added. It was washed with water three times. The organic layers were dried over MgSO ₄ , filtered and the solvent removed. The product was purified by column chromatography on S1O2 with Hex/EtOAc gradient (9: 1 to 8:2 to 7:3) yielding a white solid. Yield: 1.75 g (42 %).

[00216] Synthesis of 5-(3-((4-((3-( 1 -(2,6-d imethy Ipheny I)- 1 H-im idazol-2- yl)phenyl)ethynyl)phenyl)ethynyl)phenyl)-1 -methyl-3-propyl-1 H-1 ,2,4- triazole intermediate (6)

[00217] 2.1 g (4.9 mmol) of intermediate (4) and 1.34 g (4.9 mmol) of intermediate (5) were dissolved in 80 mL of a 1 : 1 mixture of THF and NEt.3. Nitrogen was bubbled through the solution for 10 min. 0.17 g (0.25 mmol) of PdCI ₂ (PPh ₃ )2 was then added followed by the addition of 93 mg (0.49 mmol) of Cul. The reaction was stirred at 65 °C over night. After cooling to room temperature, 100 mL of CH2CI2 were added and it was washed with cone. NH ₄ OH three times to remove the copper catalyst. After two washings with water, the organic layer was dried over MgSO ₄ . After filtration and removal of the solvent the crude mixture was purified by column chromatography on silica gel with Hex/EtOAc 1 : 1 leading to the desired product as confirmed by ¹ H-NMR.

[00218] Synthesis of asymmetric tetradentate ligand L49

[00219] The purified intermediate (6) was placed in a thick-wall Schlenk flask.

Methanol was added. It was degassed with three cycles of evacuation and refilling with nitrogen. Palladium on activated carbon (10 wt % loading) was added. The reaction mixture was degassed again three times. The flask was then set under a pressure of 2 bar of hydrogen gas and the nnixture was stirred at room temperature for seven days. The reaction mixture was then filtered through a pad of celite to remove the catalyst and the solvent was removed to obtain the expected ligand as a colorless oil. Yield: 1.6 g

¹ H-NMR (400 MHz, CDCIs): δ 7.56 - 7.28 (m, 7H), 7.23 - 6.88 (m, 10H), 3.89 (s, 3H), 3.1 1 - 2.70 (m, 10H), 2.07 (s, 6H), 1.88 (dd, 2H), 1.08 (t, 3H)

[00220] m/z (LCMS): calcd. 580.34 ([M+H ⁺ ]), found, 580.53

[00221] b)Synthesis of the additional bidentate C ^A C ligand L' ₄

[00222]

[00223] Synthesis of 1 -phenyl-1 H-benzo[c/]imidazole (7)

[00224] In an oven-dried two neck 250 ml_ round-bottom flask, Cul (646 mg; 3.4 mmol; 0.1 eq.), 1 H-benzo[c/] imidazole (4 g; 33.9 mmol; 1 eq.) and CSCO3 (22.1 g; 67.8 mmol; 2 eq.) in anhydrous DMF (65 ml_) were introduced. The reaction mixture was deoxygenated for 20 min by N2 bubbling. Then, iodobenzene (8.3 g; 4.5 ml_; 40.6 mmol; 1.2 eq.) and 1 ,10-phenanthroline (1.2 g; 6.8 mmol; 0.2 eq) were successively added. The resulting mixture was heated at 1 10 °C for 24 hours in the dark under inert atmosphere. After that reaction time, additional iodobenzene (3.6 g; 2 ml_; 18 mmol; 0.5 eq.) was added, and the reaction was heated at 1 10 °C for one extra day. After this reaction time, the reaction mixture was cooled to room

temperature and filtered. The filtered solids were washed with 120 ml_ of ethyl acetate. The filtrate was concentrated under vacuum. In order to remove the DMF, water (100 ml_) was added to the residue and the aqueous phase was subsequently extracted with more ethyl acetate (3 x 30 ml_). The combined organic layers were dried over MgSO ₄ and the solvent removed using a rotary evaporator (rotavap). The residue was purified on column chromatography employing mixtures of hexane:ethyl acetate (2: 1 - 0: 1). The product was obtained as a yellow liquid. Yield: 4.8 g; 27.7 mmol; 73%.

[00225] ¹ H NMR (400 MHz, DMSO-de) δ 8.56 (s, 1 H), 7.78 (dd, J = 6.5, 2.4 Hz, 1 H), 7.73 - 7.59 (m, 5H), 7.51 (dd, J = 10.2, 4.3 Hz, 1 H), 7.38 - 7.26 (m, 2H).

[00226] Synthesis of 3-methyl-1 -phenyl-1 H-benzo[c/]imidazol-3-ium ligand L' ₄

[00227] In a 50 mL round-bottom flask, 1 -phenyl- 1 H-benzo[c/] imidazole

intermediate 7 (4.8 g; 25 mmol; 1 eq.) and CH ₃ I (8.8 g; 3.9 mL; 62 mmol; 2.5 eq.) were introduced in toluene (2 mL). The mixture was heated at 1 10 °C for 6 hours. After that time, a white precipitate appeared. The

precipitate was then washed with THF (20 mL) and toluene (20 mL). The product was obtained as a white microcrystalline powder. Yield: 8.1 g; 24 mmol; 96 %.

[00228] ¹ H NMR (400 MHz, CDCI3) δ 1 1.05 (s, 1 H), 7.85 (dd, J = 18.2, 8.6 Hz,

3H), 7.76 - 7.55 (m, 6H), 4.47 (s, 3H).

[00229] c) Preparation of (cyclooctadiene)(1-methyl-3-phenyl-2,3-dihydro-1 H- benzo[d]imidazol-2-yl)iridium(l) chloride [lr(NHC)(COD)CI] iridium carbene precursor complex

[00230] The synthesis was carried out according to a slightly modified procedure from the one reported in Dalton Trans. 2013, 42, 7318-7329.

[00231] Dry THF (120 mL) was added to a 2-neck round-bottom flask containing 3- methyl-1-phenyl-1 /-/-benzo[c/]imidazol-3-ium additional bidentate ligand L' ₄ (1.0 g; 3.0 mmol; 2 eq.), [lr(COD)CI] ₂ (1.0 g; 1.5 mmol; 1 eq.) and

NaN(SiMe3)2 (0.6 g; 3.0 mmol; 2 eq.) under nitrogen atmosphere. A color change from yellow to dark brown was observed. The reaction mixture was degassed by nitrogen bubbling for 20 minutes and allowed to stir for 3 h protected from light with aluminum foil. After this time, the solvent was removed in vacuo and the residue purified by column chromatography on silica employing mixtures of cyclohexane:DCM (2: 1 - 1 : 1 v/v). The product was obtained as a bright yellow/green microcrystalline solid. Yield: 1.5 g; 2.76 mmol; 93 %.

[00232] ¹ H NMR (400 MHz, CD ₂ CI ₂ ) δ 8.00 (d, J = 7.1 Hz, 2H), 7.54 (dd, J = 1 1.6, 7.3 Hz, 3H), 7.41 (d, J = 7.9 Hz, 1 H), 7.31 (dd, J = 12.2, 7.8 Hz, 2H), 7.24 (d, J = 8.1 Hz, 1 H), 4.80 (m, 1 H), 4.69 (m, 1 H), 4.16 (s, 3H), 3.1 1 (m, 1 H), 2.49 (m, 1 H), 2.12 (m, 2H), 1.75 (m, 1 H), 1.64 (m, 2H), 1.34 (m, 1 H), 1.21 (m, 1 H), 1.07 (m, 1 H).

[00233] d) Synthesis of complex IV wherein the additional bidentate C ^A C ligand L' correspond to general formula (8) and more specifically to general formula (28)

[00234] In a 2-neck flask was placed 0.31 g (0.53 mmol) of asymmetric

tetradentate ligand L49 in 350 ml_ of 2-ethoxyethanol. Argon was bubbled through the solution and it was covered in aluminum foil to protect the reaction mixture from light. 0.32 g (0.59 mmol) of the Ir carbene precursor complex from step (c) were added, followed by the addition of 93 mg (0.56 mmol) of silver acetate. The mixture was further degassed by bubbling argon for another 15 min and then heated to 70 °C for 1 h. It was then further heated to 150 °C over night. The solvent was removed and the crude product was purified by column chromatography on silica gel (DCM/MeOH 1 % to 5 %) leading to a mixture of isomers of the expected complex as a light yellow oil as confirmed by ¹ H-NMR analysis and MALDI-TOF mass spectrometry. Yield: 53 mg.