Fluorescent organic light emitting elements having high efficiency

A compound of formula I

• wherein
• X is independently in each occurrence O, S or NR9,
• Y1, Y2, Y3 and Y4 are independently of each other a direct bond, or a group of formula —[A1]—[A2]y—, wherein
• A1 and A2 are independently of each other —CH═CH—, —C≡C— or a C6-C10arylene group, which may optionally be substituted by one or more C1-C25alkyl groups;
• y is 0, or 1;
• R1, R2, R3 and R4 are independently of each other H, D, F, Cl, a C1-C25alkyl group, a C1-C25alkoxy group, a C6-C10aryloxy group, or a donor group of formula
• X1 is O, S, N(R15), C(═O), C(R16)(R17), B(R18), or Si(R19)(R20),
• R9 is H, a C1-C25alkyl group, or a C6-C10aryl group;
• R10, R11, R21 and R21′ are independently of each other H, D, F, Cl, or a C1-C25alkyl group;
• R15, R16, R17, R18, R19 and R20 are independently of each other H, D, a C1-C25alkyl group, or a C6-C14aryl group, which can optionally be substituted by one, or more groups selected from a C1-C25alkyl group, a C1-C25alkoxy group and a C6-C10aryloxy group;
• with the proviso that at least one donor group of formula (Xa), or (Xd) is present in the compound of formula (I).