Synthesis and properties of bay-functionalized 9,9-bifluorenylidene derivatives

Here, we disclose the effect of substitution at the bay-region of 9,9 '-bifluorenylidene on its optical and electrochemical properties. Bay-brominated 9,9 '-bifluorenylidene was synthesized by the reductive dimerization of 4,5-dibromofluorenone with triethyl phosphite. The subsequent Suzuki-Miyaura cross-coupling afforded arylated derivatives. X-ray diffraction analysis revealed that the bulky bay-substituents twist the overall structure through the relay of the steric repulsion from the bay-region to the fjord-region. The pi-extension at the bay-region with tolyl and 4-dimethylaminophenyl groups increases the electron-donating ability, while the introduction of bromo groups enhances the electron-accepting ability.