Versatility of Terpyridine-Functionalised Aryl Tetrazoles: Photophysical Properties, Ratiometric Sensing of Zinc Cations and Sensitisation of Lanthanide Luminescence

Four new tetrazole-containing species, in conjugation with terpyridine moieties through phenyl or pyridyl linkers, have been synthesised and characterised. In the series, the tetrazole functional groups are either in their acidic form or are alkylated at the N2 position with a methyl group. The photophysical properties of the species reveal moderate UV or efficient blue fluorescent emission, with photoluminescence quantum yields of around 30 % and 80 % for UV and blue emission, respectively. The spectral profiles can be reversibly modulated through protonation/deprotonation, with changes being consistent with an increase of the electron density on the tetrazole rings upon deprotonation or a decrease of the electron density on the terpyridines through protonation. The tetrazole-containing species were also investigated for fluorescence sensing of biologically and environmentally important metal ions, highlighting a ratiometric response to the presence of Zn2+. Furthermore, this ratiometric response could be well discriminated from that of interfering Cd2+ions. Lastly, the species have been investigated as ligands for Eu3+and Yb3+cations, revealing efficient sensitisation, to give typical red and near-infrared emissions, respectively.