Compound comprising a structural unit of formula (I-1 or I-2) wherein A 1 and A 2 are independently of each other mono- or polycyclic aromatic or heteroaromatic ring systems annealed to the neighboring azaborinine ring, with A 1 and A 2 being selected from the group consisting of the following formulae (II-1) to (11-29); wherein X 1 and X 2 are independently of each other selected from the group consisting of O, S, Se, NR 3 , CR 3 2 and SiR 3 2 , with R 3 being H, alkyl with 1 to 12 C-atoms or phenyl; and wherein each aromatic ring carbon atom that is not a fusion atom may be replaced by N; B 1 is a mono- or polycyclic aromatic or heteroaromatic ring system annealed to the two neighboring azaborinine rings, with B 1 selected from the group consisting of the following formulae (III-1) to (III-42) and (III-46); wherein X 1 , X 2 and X 3 are independently of each other selected from the group consisting of O, S, Se, NR 3 , CR 3 2 and SiR 3 2 , with R 3 being R 0 as defined above; wherein a may be 0 or 1; and wherein each aromatic ring carbon atom that is not a fusion atom may be replaced by N; Ar 1 and Ar 2 are independently of each other phenyl or phenyl wherein one or more aromatic ring atom may be replaced by N; and R 1 and R 2 are independently of each other selected from the group consisting of hydrogen, alkyl having from 1 to 20 carbon atoms, aryl having from 5 to 30 aromatic ring atoms and heteroaryl having from 5 to 30 aromatic ring atoms; wherein A 1 , A 2 , B 1 , Ar 1 and Ar 2 may independently of each other be unsubstituted or substituted with a substituent L selected from halogen, or alkyl, alkoxy, oxaalkyl, thioalkyl, fluoroalkyl and fluoroalkoxy with 1 to 12 C atoms or alkenyl and alkynyl with 2 to 12 C atoms; and wherein an asterisk ("*") denotes a linkage to an adjacent unit or group. A 1 and A 2 are independently of each other mono- or polycyclic aromatic or heteroaromatic ring systems annealed to the neighboring azaborinine ring, with A 1 and A 2 being selected from the group consisting of the following formulae (II-1) to (11-29); wherein X 1 and X 2 are independently of each other selected from the group consisting of O, S, Se, NR 3 , CR 3 2 and SiR 3 2 , with R 3 being H, alkyl with 1 to 12 C-atoms or phenyl; and wherein each aromatic ring carbon atom that is not a fusion atom may be replaced by N; B 1 is a mono- or polycyclic aromatic or heteroaromatic ring system annealed to the two neighboring azaborinine rings, with B 1 selected from the group consisting of the following formulae (III-1) to (III-42) and (III-46); wherein X 1 , X 2 and X 3 are independently of each other selected from the group consisting of O, S, Se, NR 3 , CR 3 2 and SiR 3 2 , with R 3 being R 0 as defined above; wherein a may be 0 or 1; and wherein each aromatic ring carbon atom that is not a fusion atom may be replaced by N; Ar 1 and Ar 2 are independently of each other phenyl or phenyl wherein one or more aromatic ring atom may be replaced by N; and R 1 and R 2 are independently of each other selected from the group consisting of hydrogen, alkyl having from 1 to 20 carbon atoms, aryl having from 5 to 30 aromatic ring atoms and heteroaryl having from 5 to 30 aromatic ring atoms; <EOS>