Compound of the formula where M is Li; X is S or O, preferably O; R is a branched or cyclic alkyl or alkoxy group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R a, where one or more non-adjacent CH 2 groups may be replaced by R a C=CR a, C≡C, Si(R a) 2, Ge(R a) 2, Sn(R a) 2, C=O, C=S, C=Se, C=NR a, P(=O)(R a), SO, SO 2, NR a, O, S or CONR a and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, or an aromatic or heteroaromatic ring system, preferably an aromatic ring system, having 5 to 60 aromatic ring atoms which contains a radical R b at least in one ortho position relative to the bonding site on the quinoline ring and may optionaally be substituted by one or more radicals R a, where the radical R preferably does not form a ring system together with the quinoline ring; R a is on each occurrence, identically or differently, H, D or an alkyl group having 1 to 20 C atoms, an aromatic ring system having 6 to 60 C ring atoms or a heteroaromatic ring system having 1 to R b 60 C ring atoms, in which, in addition, H atoms may be replaced by D or F; two or more adjacent substituents R a here may also form a mono- or polycyclic, aliphatic, aromatic or heteroaromatic ring system with one another, where it is preferred for two or more adjacent radicals R a not to form a ring closure; is on each occurrence, identically or differently, an alkyl group having 1 to 20 C atoms, an aromatic ring system having 6 to 60 C ring atoms or a heteroaromatic ring system having 1 to 60 C ring atoms, where H atoms may be replaced by D or F; two or more adjacent substituents R b here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another, where it is preferred for two or more adjacent radicals R b not to form a ring closure; n is 1; with the proviso that, if R is an aromatic ring system which contains a radical R b in only one ortho position to the quinoline ring, the radical R b has at least 2 C atoms, preferably at least 3 C atoms and very preferably at least 4 C atoms, and where R is bonded to the quinoline ring at position 2. M is Li; X is S or O, preferably O; R is a branched or cyclic alkyl or alkoxy group having 3 to 40 C atoms, which may in each case be substituted by one or more radicals R a, where one or more non-adjacent CH 2 groups may be replaced by R a C=CR a, C≡C, Si(R a) 2, Ge(R a) 2, Sn(R a) 2, C=O, C=S, C=Se, C=NR a, P(=O)(R a), SO, SO 2, NR a, O, S or CONR a and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2, or an aromatic or heteroaromatic ring system, preferably an aromatic ring system, having 5 to 60 aromatic ring atoms which contains a radical R b at least in one ortho position relative to the bonding site on the quinoline ring and may optionaally be substituted by one or more radicals R a, where the radical R preferably does not form a ring system together with the quinoline ring; R a is on each occurrence, identically or differently, H, D or an alkyl group having 1 to 20 C atoms, an aromatic ring system having 6 to 60 C ring atoms or a heteroaromatic ring system having 1 to R b 60 C ring atoms, in which, in addition, H atoms may be replaced by D or F; two or more adjacent substituents R a here may also form a mono- or polycyclic, aliphatic, aromatic or heteroaromatic ring system with one another, where it is preferred for two or more adjacent radicals R a not to form a ring closure; is on each occurrence, identically or differently, an alkyl group having 1 to 20 C atoms, an aromatic ring system having 6 to 60 C ring atoms or a heteroaromatic ring system having 1 to 60 C ring atoms, where H atoms may be replaced by D or F; two or more adjacent substituents R b here may also form a mono- or polycyclic, aliphatic or aromatic ring system with one another, where it is preferred for two or more adjacent radicals R b not to form a ring closure; n is 1;