2,3,4,5-Tetrafunctionalized siloles: Syntheses, structures, luminescence, and electroluminescence

Six new diethynylsilane compounds with the general formula Si(Cequivalent toC-R)(2)R'(2) (R = p-N-indolylphenyl, R' = Me, 1; R' = Ph, 2; R = p-N-7-azaindolylphenyl, R' = Me, 3; R' = Ph, 4; R = p-2,2'-dipyridylaminophenyl, R' = Me, 5; R' = Ph, 6) have been synthesized and fully characterized. Compounds 1, 2, and 4 have been found to undergo intramolecular cyclization in the presence of Li-naphthyl to form the corresponding 2,5-dilithiosiloles, which after methylation by CH3I or undergoing Pd-catalyzed cross-coupling reactions with the appropriate arylbromide produced six new silole compounds: 1,1-diphenyl-2,5-dimethyl-3,4-bis(4-N-7-azaindoylphenyl)silole (7), 1,1-diphenyl-2,3,4,5-tetrakis(4-N-indoylphenyl)silole (8), 1,1dimethyl-2,5-bis(4-N-7-azaindoylphenyl)-3,4-bis(4-N-indoylphenyl)silole (9), 1,1-dimethyl-2,5-bis(p-2,2'-dipyridylaminophenyl)-3,4-(4-N-indoylphenyl)silole (10), 1,1-dimethyl-2,5-bis(4-(N-1-naphthylphenylamino)phenyl)-3,4-bis(4-N-indoylphenyl)silole (11), and 1,1-dimethyl-2,5-bis(4'-(N-1-naphthylphenylamino)biphenyl)-3,4-bis(4-N-indoylphenyl)silole (12). Compounds 8-12 are a new class of silole molecules that are functionalized at the 2-, 3-, 4-, and 5-positions by indolylphenyl, 7-azaindolylphenyl, 2,2'-dipyridylaminophenyl, (N-l-naphthyl)-(N-phenyl)aminophenyl, or (N-1-naphthyl)(N-phenyl)aminobiphenyl. The structures of compounds 3, 5, and 8 were determined by single-crystal X-ray diffraction analysis. Siloles 8-12 emit a green color in solution and the solid state, while in contrast silole 7 emits a blue color with the emission maximum at 445 nm. The effects of substituent groups at different positions of the silole ring on structures and luminescent properties have been examined. A single-layer EL device with compound 11 being sandwiched between the ITO anode and the LiF/Al cathode layers has been fabricated successfully.