A tetraazaperopyrene compound of formula (I): wherein: R1, R2, R3, R4, R5, R6, R7, R8 at each occurrence, independently are selected from H, Cl and Br, with the proviso that at least one of R1, R2, R3, R4, R5, R6, R7 and R8 is Cl or Br, R9, R10, at each occurrence, independently are selected from H, a C1-30 alkyl group, a C1-30 haloalkyl group, a C6-14 aryl group, a heteroaryl group having 5 to 14 ring atoms, and a C7-20 arylalkyl group, wherein aryl, heteroaryl and arylalkyl can be optionally substituted with one or more halogen, C1-4 haloalkyl, —CN, —NO2, —CHO, —COOH, —CONH2, —CO(C1-14 alkyl), —COO(C1-14 alkyl), —CONHC(C1-14 alkyl) and —CON(C1-14 alkyl)2 groups.