Triarylboranes with a 2-dimesitylboryl-2'-(N,N-dimethylamino)biphenyl core unit: structure-property correlations and sensing abilities to discriminate between F(-) and CN(-) ions.

Abstract

A series of triarylboranes, in which different substituents are introduced at the para position of the dimethylamino group of a 2-dimesitylboryl-2'-(N,N-dimethylamino)biphenyl core unit, have been comprehensively investigated to explore the effect of structural modification on photophysical properties. The introduction of electron-accepting substituents would facilitate the HOMO→LUMO charge transfer (CT) transition. In contrast, the intramolecular CT transition is significantly prohibited when electron-donating substituents are incorporated. Notably, the HOMO→LUMO CT transition mainly consists of the transition from the electron-donating amino group to an electron acceptor other than boryl when a strong electron acceptor such as the dicyanovinyl group is present. This dicyanovinyl-substituted compound displays sensing abilities to discriminate fluoride and cyanide ions. In solution in THF, the fluoride ions first bind to the boron center, then attack the α-carbon atom of the dicyanovinyl group, whereas the cyanide anion acts on the electron-accepting centers in the reverse sequence. As a result, the absorption and emission change in different manners upon addition of fluoride and cyanide ions.