Effect of Ethynyl and 2‐Thienyl Substituents on the Complexation of 4′‐Substituted 2,2′:6′,2″‐Terpyridines with Zn 2+ and Fe 2+ Ions, and the Spectroscopic Properties of the Ligands and Formed Complex Species

The complexation of terpyridine ( tpy ) and its 4′‐ethynyl (E) and 4′‐(2‐thienyl) (T) derivatives, as promising chelate end groups for oligomeric components of conjugated metallosupramolecular polymers, with Zn 2+ and Fe 2+ ions as ion couplers was investigated in acetonitrile using NMR and UV/Vis spectroscopy. The binding of these ligands with Zn 2+ ions shows two distinct steps with comparable binding constants in the range of 10 6 dm 3  mol –1 , whereas their binding with Fe 2+ ions shows a strong tendency to form [FeL 2 ] 2+ species, which almost do not dissociate to monoligand species [FeL] 2+ even at a twofold excess of Fe 2+ ions. The ligand exchange dynamics between [ZnL 2 ] 2+ species in solution was studied by NMR spectroscopy and the related parameters were determined. UV/Vis spectra taken during complexation show an apparent isosbestic point at 310 ± 10 nm, and those of the systems with Fe 2+ ions also show a metal‐to‐ligand charge‐transfer band at 550–580 nm. 4′‐Substituents strongly enhance the luminescence of tpy (ca. 400 times). Additional enhancement is provided by binding the ligands to Zn 2+ ions, whereas their binding to Fe 2+ ions quenches the fluorescence.