A compound comprising one or more divalent units of formula I wherein R 1 on each occurrence identically or differently, denotes H or straight chain, branched or cyclic alkyl group with 1 to 30 C atoms in which one or more non-adjacent CH 2 groups are optionally replaced, in each case independently from one another, by -O-, -S-, -C -,-C O-, -O-C -, -O-CO -O-, -SO 2 -, -SO 3 -, -NR 0 -,-SiR 0 R 00 -, -CF 2 -, -CR 0 =CR 00 -, -CY 1 =CY 2 - or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, and in which one or more H atoms are optionally replaced by F, Cl, Br, I or CN, or denotes monocyclic or polycyclic aryl or heteroaryl, each of which is optionally substituted with one or more groups R S and has 4 to 30 ring atoms, X is O or S, A1 is thiophene, A2, A3 denote, independently of each other, and on each occurrence identically or differently, a monocyclic or polycyclic aromatic or heteroaromatic group with 4 to 20 ring atoms that is optionally substituted by one or more groups R S, R S denotes, on each occurrence identically or differently, F, Br, Cl, -CN, -NC, -NCO, -NCS, -OCN, -SCN,-C NR 0 R 00, -C X 0, -C R 0, -C OR 0, -NH 2,-NR 0 R 00, -SH, -SR 0, -SO 3 H, -SO 2 R 0, -OH, -NO 2, -CF 3,-SF 5, optionally substituted silyl, carbyl or hydrocarbyl with 1 to 40 C atoms that is optionally substituted and optionally comprises one or more hetero atoms, R 0, R 00 independently of each other denote H or optionally substituted C 1-40 carbyl or hydrocarbyl, and preferably denote H or alkyl with 1 to 12 C-atoms, Y 1, Y 2 independently of each other denote H, F, Cl or CN, X 0 denotes halogen, preferably F, Cl or Br, r, s are independently of each other 0, 1, 2, 3 or 4. R 1 on each occurrence identically or differently, denotes H or straight chain, branched or cyclic alkyl group with 1 to 30 C atoms in which one or more non-adjacent CH 2 groups are optionally replaced, in each case independently from one another, by -O-, -S-, -C -,-C O-, -O-C -, -O-CO -O-, -SO 2 -, -SO 3 -, -NR 0 -,-SiR 0 R 00 -, -CF 2 -, -CR 0 =CR 00 -, -CY 1 =CY 2 - or -C≡C- in such a manner that O and/or S atoms are not linked directly to one another, and in which one or more H atoms are optionally replaced by F, Cl, Br, I or CN, or denotes monocyclic or polycyclic aryl or heteroaryl, each of which is optionally substituted with one or more groups R S and has 4 to 30 ring atoms, X is O or S, A1 is thiophene, A2, A3 denote, independently of each other, and on each occurrence identically or differently, a monocyclic or polycyclic aromatic or heteroaromatic group with 4 to 20 ring atoms that is optionally substituted by one or more groups R S, R S denotes, on each occurrence identically or differently, F, Br, Cl, -CN, -NC, -NCO, -NCS, -OCN, -SCN,-C NR 0 R 00, -C X 0, -C R 0, -C OR 0, -NH 2,-NR 0 R 00, -SH, -SR 0, -SO 3 H, -SO 2 R 0, -OH, -NO 2, -CF 3,-SF 5, optionally substituted silyl, carbyl or hydrocarbyl with 1 to 40 C atoms that is optionally substituted and optionally comprises one or more hetero atoms, R 0, R 00 independently of each other denote H or optionally substituted C 1-40 carbyl or hydrocarbyl, and preferably denote H or alkyl with 1 to 12 C-atoms, Y 1, Y 2 independently of each other denote H, F, Cl or CN, X 0 denotes halogen, preferably F, Cl or Br, r, s are independently of each other 0, 1, 2, 3 or 4.