Electron-donating abilities and luminescence properties of tolane-substituted nido-carboranes

The luminescence properties of nido-carborane (7,8-dicarba-nido-carborate anion)-substituted tolane derivatives were investigated. It was shown that the nido-carborane unit acted as an electron-donating group in all derivatives, and their emission colors can be tuned by the substituents at the tolane moiety. According to theoretical investigation, it was proposed that frontier orbitals were distinctly separated by the twisted structure of the methyl substituents at the nido-carborane unit. Thus, in the absorption spectra, drastic changes were obtained because the HOMO-LUMO transition was forbidden. These structural and electrical substituent effects should serve as good guidelines for designing optoelectronic materials based on nido-carboranes.