Colorimetric fluoride ion sensing by boron-containing pi-electron systems

The boron-containing pi-conjugated systems, including tri(9-anthryl)borane (1) and tris[(10-dimesitylboryl)-9-anthryl]borane (2), have been investigated as a new type of fluoride chemosensor. Upon complexation of 1 with a fluoride ion, a significant color change from orange to colorless was observed and, in the UV-visible absorption spectra, the characteristic band of 1 at 470 nm disappeared and new bands around 360-400 nm assignable to pi-pi transitions of the anthryl moieties were observed. This change can be rationalized as a result of the interruption of the pi-conjugation extended through the vacant p-orbital of the boron atom by the formation of the corresponding fluoroborate. The binding constant of compound 1 with the fluoride ion was quite high [(2.8 +/- 0.3) x 10(5) M(-1)], whereas 1 only showed small binding constants with AcO- and OH- of around 10(3) M(-1) and no sensitivity to other halide ions such as Cl-, Br-, and I-, thus demonstrating its selective sensing ability to the fluoride ion. In contrast to the monoboron system 1, compound 2 having four boron atoms showed multistage changes in the absorption spectra by the stepwise complexation with fluoride ions.

Toward new materials for organic electroluminescent devices: synthesis, structures, and properties of a series of 2,5-diaryl-3,4-diphenylsiloles

A series of 2,5-diaryl-3,4-diphenylsiloles, with various mono-substituted phenyl groups, extended pi-conjugated groups, and heteroaryl groups as aryl groups at the 2,5-positions, has been prepared by a one-pot synthesis from bis(phenylethynyl)silanes based on the intramolecular reductive cyclization followed by the palladium-catalyzed cross-coupling with aryl halides. Crystal structures and chemical reactivities toward the alkaline desilylation reactions have been studied on the 2,5-bis(p-mono-substituted phenyl)silole derivatives to elucidate the effects of the p-substituents. The UV-visible absorption and fluorescence spectra, and cyclic voltammetry of the 2,5-diarylsiloles have been systematically evaluated. Their photophysical properties as well as their electronic structures significantly depend on the nature of the 2,5-aryl groups.

Reaction of Hypercoordinate Dichlorosilanes Bearing 8-(Dimethylamino)-1-naphthyl Group(s) with Magnesium: Formation of the 1,2-Disilaacenaphthene Skeleton

Migration of NMe(2) from C(naphthyl) to Si and Si-Si and Si-C bond formation to give a 1,2-disilaacenaphthene skeleton occurred in the reaction of hypercoordinate dichlorosilanes bearing the 8-(dimethylamino)-1-naphthyl group with two equivalents of magnesium [e.g., Eq. (a)]. The intermediate was isolated as the 1-isopropoxy derivative after quenching the reaction mixture with isopropyl alcohol.