Compound of formula I wherein the individual groups have the following meanings R 1 and R 2 denote -C≡C-R 3, wherein R 3 is a group of formula II -AR'R"R"' II wherein A is C, Si or Ge, preferably Si, R', R", R"' are identical or different groups selected from the group consisting of H, a straight-chain, branched or cyclic alkyl or alkoxy group having 1 to 20 C atoms, a straight-chain, branched or cyclic alkenyl group having 2 to 20 C atoms, a straight-chain, branched or cyclic alkynyl group having 2 to 20 C atoms, a straight-chain, branched or cyclic alkyl-carbonyl group having 2 to 20 C atoms, an aryl or heteroaryl group having 4 to 20 ring atoms, an arylalkyl or heteroarylalkyl group having 4 to 20 ring atoms, an aryloxy or heteroaryloxy group having 4 to 20 ring atoms, or an arylalkyloxy or heteroarylalkyloxy group having 4 to 20 ring atoms, wherein all the aforementioned groups are optionally substituted with one or more groups L', L' has one of the meanings given for L, L is selected from F, Cl, Br, I, -OH, -CN, -NO 2, -NCO, -NCS, -OCN, -SCN, -C(=O)NR 0 R 00, -C(=O)X 0, -C(=O)R 0,-NR 0 R 00, C(=O)OH, aryl or heteroaryl having 4 to 20 ring atoms, straight chain, branched or cyclic alkyl, alkoxy, oxaalkyl or thioalkyl with 1 to 20, preferably 1 to 12 C atoms which is unsubstituted or substituted with one or more F or Cl atoms or OH groups, and straight chain, branched or cyclic alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 2 to 30, preferably 2 to 12 C atoms which is unsubstituted or substituted with one or more F or Cl atoms or OH groups, X 0 is halogen, R 0, R 00 independently of each other denote H or alkyl with 1 to 20 C-atoms. R 1 and R 2 denote -C≡C-R 3, wherein R 3 is a group of formula II A is C, Si or Ge, preferably Si, R', R", R"' are identical or different groups selected from the group consisting of H, a straight-chain, branched or cyclic alkyl or alkoxy group having 1 to 20 C atoms, a straight-chain, branched or cyclic alkenyl group having 2 to 20 C atoms, a straight-chain, branched or cyclic alkynyl group having 2 to 20 C atoms, a straight-chain, branched or cyclic alkyl-carbonyl group having 2 to 20 C atoms, an aryl or heteroaryl group having 4 to 20 ring atoms, an arylalkyl or heteroarylalkyl group having 4 to 20 ring atoms, an aryloxy or heteroaryloxy group having 4 to 20 ring atoms, or an arylalkyloxy or heteroarylalkyloxy group having 4 to 20 ring atoms, wherein all the aforementioned groups are optionally substituted with one or more groups L', L' has one of the meanings given for L, L is selected from F, Cl, Br, I, -OH, -CN, -NO 2, -NCO, -NCS, -OCN, -SCN, -C(=O)NR 0 R 00, -C(=O)X 0, -C(=O)R 0,-NR 0 R 00, C(=O)OH, aryl or heteroaryl having 4 to 20 ring atoms, straight chain, branched or cyclic alkyl, alkoxy, oxaalkyl or thioalkyl with 1 to 20, preferably 1 to 12 C atoms which is unsubstituted or substituted with one or more F or Cl atoms or OH groups, and straight chain, branched or cyclic alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 2 to 30, preferably 2 to 12 C atoms which is unsubstituted or substituted with one or more F or Cl atoms or OH groups, X 0 is halogen, R 0, R 00 independently of each other denote H or alkyl with 1 to 20 C-atoms.