Polymers comprising at least one unit of formula 1 and compounds of the formula 1′ wherein, in formulae 1 and 1′ n is 0, 1, 2, 3 or 4 m is 0, 1, 2, 3 or 4 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, C1-30-alkyl, C2-30-alkenyl, C2-30-alkynyl, C5-12-cycloalkyl, C6-18-aryl, 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 hetero-aryl, 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.