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.