Superaromatic terpyridines based on corannulene responsive to metal ions

Two superaromatic terpyridine ligands (1 and 2) incorporating a corannulene unit at the 4'-position are reported. The optical and metal sensing properties of both ligands were investigated by the naked eye, and UV-vis and fluorescence spectroscopy in this work. In 1, the corannulene motif is directly connected to the 4'-phenylterpyridine domain, while in 2, the corannulene motif and the 4'-phenylterpyridine domain are separated by an acetylene linker. Both 1 and 2 can work as chemosensors for metal ions and display different optical responses to various metal ions. It is shown that both ligands exhibit a colorimetric sensing ability for Fe2+ through an obvious color change from colorless to magenta, and this color change can be observed easily by the naked eye. The addition of Fe2+ also leads to significant changes in the absorption spectra of the ligands. A characteristic red shift in the emission spectra is observed in the presence of Zn2+, which facilitates the discrimination of Zn2+ from other metal ions. In addition, density functional theory (DFT) and time-dependent-density functional theory (TD-DFT) calculations were performed and shown to be consistent with the observed experimental results.