Electroluminescent materials and devices

1. An electroluminescent compound of formula:

wherein

L is a ligand selected from the group consisting of (i) and (ii) as follows:

and

wherein: M is ruthenium, rhodium, palladium, osmium, iridium or platinum;

n is 1 or 2;

the number of ligands (i) or (ii) in the electroluminescent compound is determined by the valence of the metal M and the quantity n so as to form an electrically neutral compound;

R 1 to R 5 which may be the same or different are selected from substituted and unsubstituted hydrocarbyl groups; substituted and unsubstituted monocyclic and polycyclic heterocyclic groups; substituted and unsubstituted hydrocarbyloxy or carboxy groups; fluorocarbyl groups; halogen; nitrile; nitro; amino; alkylamino; dialkylamino; arylamino; diarylamino; N-alkylamido, N-arylamido, sulfonyl and thiophenyl; and R 2 and R 3 can additionally be alkylsilyl or arylsilyl;

p, s and t independently are 0, 1, 2 or 3;

q and r independently are 0, 1 or 2, subject to the provisos that:

where p is 2, one of the R 1 groups is selected from saturated hydrocarbyl and halogen and the other is as defined above;

where p is 3, two of the R 1 groups are selected from saturated hydrocarbyl and halogen and the other is as defined above;

where q is 2, one of the R 2 groups is selected from saturated hydrocarbyl and halogen and the other is as defined above;

where r is 2, one of the R 3 groups is selected from saturated hydrocarbyl and halogen and the other is as defined above;

where s is 2, one of the R 4 groups is selected from saturated hydrocarbyl and halogen and the other is as defined above;

where s is 3, two of the R 4 groups are selected from saturated hydrocarbyl and halogen and the other is as defined above;

where t is 2, one of the R 5 groups is selected from saturated hydrocarbyl and halogen and the other is as defined above; and

where t is 3, two of the R 5 groups are selected from saturated hydrocarbyl and halogen and the other is as defined above.

2. The compound of claim 1 , wherein M is iridium.

3. The compound of claim 1 , wherein n is 1.

4. The compound of claim 1 , wherein the compound includes at least one substituent group R 1 to R 5 which is selected from the group consisting of substituted and unsubstituted aliphatic and cycloaliphatic groups.

5. The compound of claim 4 , wherein the at least one substituent group R 1 to R 5 is alkyl or alkoxy.

6. The compound of claim 4 , wherein the at least one substituent group R 1 to R 5 is methyl, ethyl, n-propyl, i-propyl, s-butyl, t-butyl, cyclohexyl, methoxy or ethoxy.

7. The compound of claim 1 , wherein the compound includes at least one substituent group R 1 to R 5 which is selected from the group consisting of substituted and unsubstituted monocyclic and polycyclic aromatic, aryloxy and heterocyclic groups.

8. The compound of claim 7 , wherein the at least one substituent group R 1 to R 5 is phenyl, tolyl, fluorophenyl, biphenyl, naphthyl, fluorenyl, anthracenyl, phenanthrenyl or carbazolyl.

9. The compound of claim 1 , wherein the compound includes at least one substituent group R 1 to R 5 which is selected from the group consisting of fluoro, chloro, methylamino, dimethylamino, benzylamino and dibenzylamino groups.

10. The compound of claim 1 , wherein the compound includes at least one substituent group R 2 or R 3 which is selected from the group consisting of trialkylsilyl and triarylsilyl.

11. The compound of claim 1 , wherein L is a ligand according to formula (i), M is Ir, n is 1 and p, q, r, s and t are 0.

12. An electroluminescent device comprising (i) a first electrode, (ii) a second electrode and (iii) an electroluminescent layer comprising an electroluminescent compound according to claim 1 located between the first electrode and the second electrode.

13. The device of claim 12 , wherein a layer of a hole transmitting material is located between the first electrode and the electroluminescent layer.

14. The device of claim 13 , in which the hole transmitting material is an aromatic amine.

15. The device of claim 13 , in which the hole transmitting material is a film of a material selected from α-NPB, poly(vinylcarbazole), N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), polyaniline, substituted polyanilines, polythiophenes, substituted polythiophenes, polysilanes and substituted polysilanes.

16. The device of claim 13 , in which the hole transmitting material is a copolymer of aniline.

17. The device of claim 13 , in which the hole transmitting material is a conjugated polymer.

18. The device of claim 17 , in which the conjugated polymer is selected from the group consisting of poly (p-phenylenevinylene) (PPV) and copolymers of PPV.

19. The device of claim 13 , in which the hole transmitting material is a film of a compound which is (a) a polymer of at least two monomers of formula

where R″ is in the ortho- or meta-position and is selected from hydrogen, C 1 to C 18 alkyl, C 1 to C 6 alkoxy, amino, chloro, bromo, hydroxy or the group:

where R′ is selected from hydrogen, C 1 to C 6 alkyl or aryl; or which is (b) a polyaniline of formula:

where p is from 1 to 10 and n is from 1 to 20, R″ is as defined above and X is an anion;

or which is (c) a compound selected from one of the following formulae:

where R, R 1 , R 2 , R 3 and R 4 can be the same or different and are selected from hydrogen; substituted and unsubstituted hydrocarbyl groups, aliphatic groups, aromatic groups, heterocyclic groups and polycyclic ring structures; fluorocarbon groups; halogens, additionally, R, R 1 , R 2 , R 3 and R 4 can also form substituted and unsubstituted fused aromatic, heterocyclic and polycyclic ring structures and can be copolymerisable with a monomer.

20. The device of claim 12 in which the electroluminescent layer comprises an electroluminescent compound in admixture with a hole transmitting material.

21. The device of claim 12 , wherein a layer of an electron transmitting material is located between an electrode that serves as a cathode and the electroluminescent layer.

22. The device of claim 21 in which the electron transmitting material is a metal quinolate.

23. The device of claim 22 , in which the metal quinolate is an aluminum quinolate, zirconium quinolate or lithium quinolate.

24. The device of claim 21 , in which the electron transmitting material is of formula Mx(DBM) n where Mx is a metal and DBM is dibenzoyl methane and n is the valency of Mx.

25. The device of claim 21 , in which the electron transmitting material is a cyanoanthracene, a polystyrene sulphonate or a compound of according to one of the following formulae:

26. The device of claim 12 , in which an electron transmitting material is in admixture with the electroluminescent compound.

27. The device of claim 12 , in which the first electrode is a transparent electrically conducting glass electrode.

28. The device of claim 12 , in which the second electrode is selected from aluminum, barium, rare earth metals, transition metals, calcium, lithium, magnesium and alloys thereof and silver/magnesium alloys.

29. The device of claim 12 , wherein the second electrode comprises a metal having a metal fluoride layer formed on it.

30. The device of claim 29 , wherein the metal fluoride is a lithium fluoride or rare earth fluoride.

31. The electroluminescent device of claim 12 , wherein L is a ligand according to formula (I), p, q, r, s and t independently are 0 or 1.

32. The compound of claim 1 , wherein L is a ligand according to formula (I), p, q, r, s, and t independently are 0 or 1.