Dopant, charge transfer salt and organic electronic device

1. A compound of formula (I):

(Core) n -(X) m    (I)

wherein Core is Ar z , wherein Ar in each occurrence independently is a C 6-20 aryl group that may be unsubstituted or substituted with one or more substituents, and z is at least 1; n is 0 and m is 1, or n is 1 and m is at least 1; and X is a group of formula (II):

wherein:

R 1 , R 4 and R 5 are each independently H or a substituent;

each R 2 is independently a C 1-40 hydrocarbyl;

R 3 is H;

one of R 1 , R 4 and R 5 is a direct bond or divalent linking group linking the group of formula (II) to Core in the case where n is 1;

x is 0, 1, 2, 3 or 4;

y is 0, 1, 2, 3 or 4; and

the compound of formula (I) is substituted with at least one ionic substituent of formula (III):

-(Sp 1 ) p -(A) q    (III)

wherein:

in the case where p=1, Sp 1 is a spacer group selected from C 1-12 alkylene wherein one or more non-adjacent C atoms may be replaced with O, S, C═O or COO; and aryl or heteroaryl that may be unsubstituted or substituted with one or more C 1-20 alkyl groups wherein one or more non-adjacent C atoms of the C 1-20 alkyl groups may be replaced with O, S, C═O or COO;

A is independently an anion selected from the group consisting of sulfonate and —COO − , or a cation selected from the group consisting of —N(R 11 ) 3 + ; —P(R 11 ) 3 + , S(R 11 ) 2 + and a heteroaromatic cation wherein R 11 in each occurrence is H or C 1-12 hydrocarbyl;

p is 0 or 1;

q is 1 if p is 0; and

q is at least 1 if p is 1, the compound of formula (I) further comprising at least one counterion B to balance the charge of the one or more anions or cations A;

and wherein:

n is 0 and at least one occurrence of at least one of R 1 , R 4 and R 5 is an ionic substituent of formula (III); or

n is 1 and Core is substituted with one or more ionic substituents of formula (III); or

n is 1, Core is not substituted with an ionic substituent and at least one of R 1 , R 4 and R 5 is an ionic substituent of formula (III).

2. A compound according to claim 1 wherein each R 2 is independently a C 1-12 alkyl.

3. A compound according to claim 1 wherein A, which may be the same or different in each occurrence, is selected from the group consisting of sulfonate and —COO − .

4. A compound according to claim 1 wherein each B is Cs + or an organic cation.

5. A compound according to claim 1 wherein each A is a cation.

6. A compound according to claim 1 wherein n is 0.

7. A compound according to claim 6 wherein at least one R 1 and/or at least one R 4 is an ionic substituent.

8. A composition comprising an organic semiconductor and a compound according to claim 1 .

9. A formulation comprising a composition according to claim 8 and at least one solvent.

10. A formulation according to claim 9 wherein at least one solvent is a polar solvent.

11. A charge transfer salt comprising an organic semiconductor doped with a compound according to claim 1 .

12. An organic electronic device comprising a layer comprising a charge-transfer salt according to claim 11 .

13. An organic electronic device according to claim 12 wherein the organic electronic device is an organic light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and the cathode and wherein the layer comprising the charge-transfer salt is an electron injection layer between the light-emitting layer and the cathode.

14. An organic electronic device according to claim 12 wherein the electron injection layer is in contact with the light-emitting layer.

15. The compound according to claim 1 wherein n is 1 and Core is a core group selected from groups of formula Ar z wherein Ar in each occurrence independently is a C 6-20 aryl group that may be unsubstituted or substituted with one or more substituents and z is at least 1.