Polymers comprising at least one unit of formulae 1 or 1' and compounds of the formulae 2 or 2' wherein, in formulae 1, 1', 2 and 2', n is 0, 1, 2, 3 or 4, m is 0, 1, 2, 3 or 4, M1 and M2 are independently of each other an aromatic or heteroaromatic monocyclic or bicyclic ring system; X is at each occurrence selected from the group consisting of O, S, Se or Te, Q is at each occurrence selected from the group consisting of C, Si or Ge, R is at each occurrence selected from the group consisting of hydrogen, C1-100-alkyl, C2-100-alkenyl, C2-100-alkynyl, C5-12-cycloalkyl, C6-18-aryl, a 5 to 20 membered heteroaryl, C(O)-C1-100-alkyl, C(O)-C5-12-cycloalkyl and C(O)-OC1-100-alkyl. R2, R2', R2", R* are at each occurrence independently selected from the group consisting of hydrogen, C1-30-alkyl, C2-30-alkenyl, C2-30-alkynyl, C5-12-cycloalkyl, C6-18-aryl, 5 to 20 membered heteroaryl, OR21, OC(O)-R21, C(O)-OR21, C(O)-R21, NR21R22, NR21-C(O)R22, C(O)-NR21R22,N[C(O)R21][C(O)R22], SR21, halogen, CN, SiRSisRSitRSiu and OH, L1 and L2 are independently from each other and at each occurrence selected from the group consisting of C6-30-arylene, 5 to 30 membered heteroarylene, (A) (B) and (C).