Highly luminescent Eu3+ and Tb3+ macrocyclic complexes bearing an appended phenanthroline chromophore

A two-component ligand system (1) containing 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) as the hosting unit for the lanthanide cations and an appended asymmetrically functionalized 1,10-phenanthroline (phen) as the chromophore was synthesized. The 1:1 complexes with Eu³⁺, Gd³⁺, Tb³⁺, and Yb³⁺ have been prepared and studied in aqueous solution. For Gd·1, a relaxivity value of 2.4 mM^-1 s^-1 has been measured at 20 MHz and 25 °C, which indicates that there are no water molecules in the first coordination sphere of the metal ion. The analysis of high resolution ¹H NMR spectra of Yb·1 supports this view and suggests the direct involvement of the phen moiety in the coordination of the metal ion. For Eu·1 and Tb·1, the absorption and luminescence spectra, the overall luminescence efficiencies, and the metal-centered (MC) lifetimes were obtained; coordination features were also determined by comparing luminescence properties in water and deuterated water. For Eu·1 and Tb·1, the overall emission sensitization (se) process in air-equilibrated water was found to be notably effective with _se = 0.21 and 0.11, respectively. A detailed study of the steps originating from light absorption at the phen unit and leadinq to MC sensitized emission was performed.