Synthesis, characterization, and optoelectronic study of three biaryl-fused closo-o-carboranes and their nido-[C2B9]− species

• A novel asymmetric biaryl-fused closo-o-carborane containing phenylthiophene was prepared.
• This novel carborane, and two others prepared previously, were reacted with fluoride to obtain their nido-[C2B9]− species.
• The nido-[C2B9]− species were found to possess high HOMO and LUMO energy levels because of the electron-rich anion species.
• In the absorption spectra of the nido-[C2B9]− species, broad bands with small molar absorption coefficients were observed, and they were assigned to the charge transfer transition.
• Efficient emission was observed in the crystalline state as well as in solution due to the shorter carbon–carbon bond length in the nido-carborane cluster and suppression of the carbon–carbon bond vibration.

A biaryl-fused closo-o-carborane with a phenylthiophene moiety was synthesized and reacted with fluoride to obtain its nido-[C2B9] − species; the reaction with fluoride to obtain nido-[C2B9]− species was also performed for biphenyl- and bithiophene-fused o-carboranes, the synthesis of which we have previously reported. The structures and optoelectronic properties of the three carboranes and their nido-[C2B9]− species were experimentally and theoretically characterized. The nido-[C2B9]− species possessed high HOMO and LUMO energy levels because of the electron-rich anion species. They also displayed charge transfer (CT) transition bands, and efficient CT emissions were observed in the crystalline as well as solution state because of the shorter carbon–carbon bond length in the nido-carborane cage and suppression of the carbon–carbon bond vibration.

Biaryl-fused closo-o-carboranes were synthesized and reacted with fluoride to obtain the nido-species. They exhibited charge transfer (CT) transition bands, and efficient CT emissions were observed in the crystalline as well as solution state.Figure optionsDownload as PowerPoint slide