Organic electroluminescent device emitting blue light

1. An organic electroluminescent device comprising a light-emitting layer B comprising:

(i) a host material H B , which has a lowermost excited singlet state energy level S1 H and a lowermost excited triplet state energy level T1 H ;

(ii) a first thermally activated delayed fluorescence (TADF) material E B , which has a lowermost excited singlet state energy level S1 E and a lowermost excited triplet state energy level T1 E ; and

(iii) a second TADF material S B , which has a lowermost excited singlet state energy level S1 S and a lowermost excited triplet state energy level T1 S ,

wherein E B transfers energy to S B and S B emits thermally activated delayed fluorescence with an emission maximum between 420 and 500 nm; and wherein the relations expressed by the following formulas (1) to (4) apply:

S 1 H >S 1 E   (1)

S 1 H >S 1 S   (2)

S 1 E >S 1 S   (3)

T 1 H >T 1 S   (4).

2. The organic electroluminescent device according to claim 1 , wherein said organic electroluminescent device is a device selected from the group consisting of an organic light emitting diode, a light emitting electrochemical cell, and a light-emitting transistor.

3. The organic electroluminescent device according to claim 1 , wherein the first TADF material E B is an organic TADF emitter.

4. The organic electroluminescent device according to claim 1 , wherein the second TADF material S B is an organic TADF emitter.

5. The organic electroluminescent device according to claim 1 , wherein the device exhibits an emission maximum λ max (D) of 440 to 470 nm.

6. The organic electroluminescent device according to claim 1 , wherein the light-emitting layer B comprises:

(i) 5-98% by weight of the host compound H B ;

(ii) 1-50% by weight of the first TADF material E B ; and

(iii) 1-50% by weight of the second TADF material S B ; and optionally

(iv) 0-93% by weight of one or more further host compounds H B2 differing from H B ; and

optionally

(v) 0-93% by weight of one or more solvents.

7. The organic electroluminescent device according to claim 1 , wherein the second TADF material S B exhibits an emission maximum λ max PMMA (S B ) and the first TADF material E B exhibits an emission maximum λ max PMMA (E B ), wherein

500 nm≥λ max PMMA ( S B )>λ max PMMA ( E B ).

8. The organic electroluminescent device according to claim 1 , wherein the first TADF material E B exhibits an emission maximum λ max PMMA (E B ) in the range of from 450 to 470 nm.

9. The organic electroluminescent device according to claim 1 , wherein the second TADF material S B exhibits an emission maximum λ max PMMA (S B ), the first TADF material E B exhibits an emission maximum λ max PMMA (E B ) and the device exhibits an emission maximum λ max (D), wherein

λ max PMMA ( S B )>λ max ( D )≥λ max PMMA ( E B ).

10. The organic electroluminescent device according to claim 1 , wherein T1 E >T1 S .

11. The organic electroluminescent device according to claim 1 , wherein

S 1 E >S 1 S ≥T 1 E >T 1 S and

S 1 E −T 1 S ≤0.4 eV.

12. The organic electroluminescent device according to claim 1 , wherein first TADF material E B and the second TADF material S B are independently from another both chosen from molecules of a structure of Formula I

wherein

n is at each occurrence independently from another 1 or 2;

X is at each occurrence independently from another CN or CF 3 ;

Z is at each occurrence independently from another selected from the group consisting of a direct bond, CR 3 R 4 , C═CR 3 R 4 , C═O, C═NR 3 , NR 3 , O, SiR 3 R 4 , S, S(O), and S(O) 2 ;

Ar EwG is at each occurrence independently from another a structure according to one of Formulas IIa to IIi

wherein # represents the binding site of the single bond linking Ar EWG to the substituted central phenyl ring of Formula I;

R 1 is at each occurrence independently from another selected from the group consisting of hydrogen, deuterium, C 1 -C 5 -alkyl, wherein one or more hydrogen atoms are optionally substituted by deuterium, and C 6 -C 18 -aryl, which is optionally substituted with one or more substituents R 6 ;

R 2 is at each occurrence independently from another selected from the group consisting of hydrogen, deuterium, C 1 -C 5 -alkyl, wherein one or more hydrogen atoms are optionally substituted by deuterium, and C 6 -C 18 -aryl, which is optionally substituted with one or more substituents R 6 ;

R a , R 3 , and R 4 is at each occurrence independently from another selected from the group consisting of hydrogen, deuterium, N(R 5 ) 2 , OR 5 , SR 5 , Si(R 5 ) 3 , CF 3 , CN, F,

C 1 -C 40 -alkyl, which is optionally substituted with one or more substituents R 5 and wherein one or more non-adjacent CH 2 -groups are optionally substituted by R 5 C═CR 5 , C≡C, Si(R 5 ) 2 , Ge(R 5 ) 2 , Sn(R 5 ) 2 , C═O, C═S, C═Se, C═NR 5 , P(═O)(R 5 ), SO, SO 2 , NR 5 , O, S, or CONR 5 ;

C 1 -C 40 -thioalkoxy, which is optionally substituted with one or more substituents R 5 and wherein one or more non-adjacent CH 2 -groups are optionally substituted by R 5 C═CR 5 , C≡C, Si(R 5 ) 2 , Ge(R 5 ) 2 , Sn(R 5 ) 2 , C═O, C═S, C═Se, C═NR 5 , P(═O)(R 5 ), SO, SO 2 , NR 5 , O, S, or CONR 5 ;

C 6 -C 60 -aryl, which is optionally substituted with one or more substituents R 5 ; and

C 3 -C 57 -heteroaryl, which is optionally substituted with one or more substituents R 5 ;

R 5 is at each occurrence independently from another selected from the group consisting of hydrogen, deuterium, N(R 6 ) 2 , OR 6 , SR 6 , Si(R 6 ) 3 , CF 3 , CN, F,

C 1 -C 40 -alkyl, which is optionally substituted with one or more substituents R 6 and wherein one or more non-adjacent CH 2 -groups are optionally substituted by R 6 C═CR 6 , C≡C, Si(R 6 ) 2 , Ge(R 6 ) 2 , Sn(R 6 ) 2 , C═O, C═S, C═Se, C═NR 6 , P(═O)(R 6 ), SO, SO 2 , NR 6 , O, S, or CONR 6 ;

C 6 -C 60 -aryl, which is optionally substituted with one or more substituents R 6 ; and

C 3 -C 57 -heteroaryl, which is optionally substituted with one or more substituents R 6 ;

R 6 is at each occurrence independently from another selected from the group consisting of hydrogen, deuterium, OPh,CF 3 , CN, F,

C 1 -C 5 -alkyl, wherein one or more hydrogen atoms are optionally, independently from each other, substituted by deuterium, CN, CF 3 , or F;

C 1 -C 5 -alkoxy,

wherein one or more hydrogen atoms are optionally, independently from each other, substituted by deuterium, CN, CF 3 , or F;

C 1 -C 5 -thioalkoxy, wherein one or more hydrogen atoms are optionally, independently from each other, substituted by deuterium, CN, CF 3 , or F;

C 6 -C 18 -aryl, which is optionally substituted with one or more C 1 -C 5 -alkyl substituents;

C 3 -C 17 -heteroaryl, which is optionally substituted with one or more C 1 -C 5 -alkyl substituents;

N(C 6 -C 18 -aryl) 2 ;

N(C 3 -C 17 -heteroaryl) 2 ; and

N(C 3 -C 17 -heteroaryl)(C 6 -C 18 -aryl);

R d is at each occurrence independently from another selected from the group consisting of hydrogen, deuterium, N(R 5 ) 2 , OR 5 , SR 5 , Si(R 5 ) 3 , CF 3 , CN, F, C 1 -C 40 -alkyl, which is optionally substituted with one or more substituents R 5 and wherein one or more non-adjacent CH 2 -groups are optionally substituted by R 5 C═CR 5 , C≡C, Si(R 5 ) 2 , Ge(R 5 ) 2 , Sn(R 5 ) 2 , C═O, C═S, C═Se, C═NR 5 , P(═O)(R 5 ), SO, SO 2 , NR 5 , O, S, or CONR 5 ;

C 1 -C 40 -thioalkoxy, which is optionally substituted with one or more substituents R 5 and wherein one or more non-adjacent CH 2 -groups are optionally substituted by R 5 C═CR 5 , C≡C, Si(R 5 ) 2 , Ge(R 5 ) 2 , Sn(R 5 ) 2 , C═O, C═S, C═Se, C═NR 5 , P(═O)(R 5 ), SO, SO 2 , NR 5 , O, S, or CONR 5 ; and

C 6 -C 60 -aryl, which is optionally substituted with one or more substituents R 5 ; and

C 3 -C 57 -heteroaryl which is optionally substituted with one or more substituents R 5 ;

wherein the substituents R a , R 3 , R 4 , or R 5 independently from each other optionally may form a mono- or polycyclic, aliphatic, aromatic, and/or benzo-fused ring system with one or more substituents R a , R 3 , R 4 , or R 5 , and

wherein the one or more substituents R d independently from each other optionally may form a mono- or polycyclic, aliphatic, aromatic, and/or benzo-fused ring system with one or more substituents R d .

13. The organic electroluminescent device according to claim 12 , wherein the first TADF material E B and the second TADF material S B both bear the same structure according to Formula I structurally only differing in one or more of R a , R 1 , R 2 , and X.

14. The organic electroluminescent device according to claim 12 , wherein Z is a direct bond at each occurrence.

15. The organic electroluminescent device according to claim 12 , wherein R a is at each occurrence independently from another selected from the group consisting of

hydrogen, deuterium, Me, i Pr, t Bu, CN, CF 3 ,

Ph, which is optionally substituted with one or more substituents independently from each other selected from the group consisting of Me, i Pr, t Bu, CN, CF 3 , and Ph;

pyridinyl, which is optionally substituted with one or more substituents independently from each other selected from the group consisting of Me, i Pr, t Bu, CN, CF 3 , and Ph;

pyrimidinyl, which is optionally substituted with one or more substituents independently from each other selected from the group consisting of Me, i Pr, t Bu, CN, CF 3 , and Ph;

carbazolyl, which is optionally substituted with one or more substituents independently from each other selected from the group consisting of Me, i Pr, t Bu, CN, CF 3 , and Ph;

triazinyl, which is optionally substituted with one or more substituents independently from each other selected from the group consisting of Me, i Pr, t Bu, CN, CF 3 , and Ph; and N(Ph) 2 .

16. The organic electroluminescent device according to claim 1 , wherein the second TADF material S B exhibits an emission maximum λ max PMMA (S B ) and the first TADF material E B exhibits an emission maximum λ max PMMA (E B ), wherein

480 nm λ max PMMA ( S B )>λ max PMMA ( E B ).