Heterocyclic bridged biphenyls

A compound of the formula

• wherein A is a 6-membered heteroaromatic ring, containing at least one heteroatom selected from nitrogen, oxygen, and sulfur,
• Z1 is
• —NA1A1′, —P(═O)A4A4′, or —SiA6A7A8
• Z2 is
• NA2A2′, —P(═O)A5A6′, or —SiA6′A7′A8′,
• Ar and Ar′ are independently of each other C6-C14 aryl, which may optionally be substituted by one or more groups selected from C1-C25 alkyl which may be optionally interrupted by —O—, or C1-C25 alkoxy,
• R1, R2, R3, R4, R5, and R6 are independently of each other hydrogen, halogen, or an organic substituent, or
• R1 and R2, R4 and R6, R2 and R3, R5 and R3, and/or R5 and R6, which are adjacent to each other, together form an aromatic or heteroaromatic ring or a ring system which can optionally be substituted,
• R7 is an organic substituent, wherein two or more substituents R7 in the same molecule may have different meanings, or can form together an aromatic or heteroaromatic ring or ring system, and
• x is 0, or an integer of 1 to 5;
• A1, A2, A1′ and A2′ are independently of each other a C6-C24 aryl group, a C2-C30 heteroaryl group, which can optionally be substituted, or a group
• wherein BU is a bridging unit, A3 and A3′ are independently or each other a C6-C24 aryl group or a C2-C30 heteroaryl group, which can optionally be substituted, or A1 and A1′ or A2 and A2′ or A3 and A3′ together with the nitrogen atom to which they are bonded form a heteroaromatic ring or ring system, and
• A4, A4′, A6, A7, A8, A5, A5′, A6′, A7′, and A8′ are independently of each other a C6-C24 aryl group or a C2-C30 heteroaryl group, which can optionally be substituted;
• with the proviso that phenazine compounds expressed by formula
• are excluded, wherein:
• each R1-R4 is an H atom, a (substituted)alkyl group, aralkyl group, aryl group, or heterocyclic group, wherein R1 and R2, and R3 and R4 may form a 5-7 membered ring together with an N atom, respectively;
• each R5-R7 is an H atom, (substituted)alkyl group, alkoxy group, halogen atom or nitro group.