Compound of the formula, or: where the following applies to the symbols and indices: X is on each occurrence, identically or differently, CR 1 or C for the bonding point of the structural element having three fused rings; R 1 is on each occurrence, identically or differently, H, D, CN, a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 2, where one or more non-adjacent CH 2 groups may be replaced by -R 2 C=CR 2 -, -C≡C-, C=O, C=S, C=Se, C=NR 2, -C(=O)O-, -C(=O)NR 2 -, NR 2, -O-, -S-, SO or SO 2 and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, or an aromatic or hetero-aromatic ring system having 5 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2; R 2 is on each occurrence, identically or differently, H, D, F, CN, a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 3, where one or more non-adjacent CH 2 groups may be replaced by -R 3 C=CR 3 -, -C≡C-, C=O, C=S, C=Se, C=NR 3, -C(=O)O-, -C(=O)NR 3 -, NR 3, -O-, -S-, SO or SO 2 and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, or an aromatic or hetero-aromatic ring system having 5 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3; R 3 is on each occurrence, identically or differently, H, D, F or an aliphatic, aromatic and/or heteroaromatic hydrocarbon radical having 1 to 20 C atoms, in which, in addition, H atoms may be replaced by F; L 1 is a bond or an aryl group having 6 to 40 C atoms or a heteroaryl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 1. X is on each occurrence, identically or differently, CR 1 or C for the bonding point of the structural element having three fused rings; R 1 is on each occurrence, identically or differently, H, D, CN, a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 2, where one or more non-adjacent CH 2 groups may be replaced by -R 2 C=CR 2 -, -C≡C-, C=O, C=S, C=Se, C=NR 2, -C(=O)O-, -C(=O)NR 2 -, NR 2, -O-, -S-, SO or SO 2 and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, or an aromatic or hetero-aromatic ring system having 5 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R 2; R 2 is on each occurrence, identically or differently, H, D, F, CN, a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 3, where one or more non-adjacent CH 2 groups may be replaced by -R 3 C=CR 3 -, -C≡C-, C=O, C=S, C=Se, C=NR 3, -C(=O)O-, -C(=O)NR 3 -, NR 3, -O-, -S-, SO or SO 2 and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, or an aromatic or hetero-aromatic ring system having 5 to 40 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3; R 3 is on each occurrence, identically or differently, H, D, F or an aliphatic, aromatic and/or heteroaromatic hydrocarbon radical having 1 to 20 C atoms, in which, in addition, H atoms may be replaced by F; L 1 is a bond or an aryl group having 6 to 40 C atoms or a heteroaryl group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R 1.