Luminescence properties and solution dynamics of lanthanide complexes composed by a macrocycle hosting site and naphthalene or quinoline appended chromophore

The two-component ligand systems 1 and 2 which contain 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) as the hosting unit for the lanthanide cations, and naphthalene (which is devoid of any chelating ability) or quinoline units, respectively, as chromophores, were synthesized. The 1:1 complexes with Gd3+, EU3+ and Tb3+ have been studied in aqueous solution. Relaxometric properties for Gd center dot 1 indicate that two water molecules (q = 2) are in the first coordination sphere of the metal ion whereas for Gd center dot 2, q < 2 is found. For Gd center dot 1, these results indicate that the naphthalene unit is not coordinated to the metal centre; for the case of quinoline, reasons for the lower hydration state are discussed. In case of Eu center dot 1, Tb center dot 1, Eu center dot 2, and Tb center dot 2 the absorption and luminescence spectra, the overall luminescence efficiencies, and the metal-centred lifetimes, were obtained both in water and deuterated water. The coordination features of these complexes were explored by comparing their luminescence properties, resulting in hydration state q = 2 and 1.4 for the cases of the complexes of I and 2, respectively. Use of the photophysical parameters in air-equilibrated water allowed the determination of the ligand-to-cation energy transfer efficiency, Phi(EnT), leading to the overall emission sensitization process. For Eu center dot 1, and Eu center dot 2, we found Phi T-En = 0.034 and 0.078, respectively, supporting that also a non-coordinating chromophore like naphthalene, case of ligand 1, can transfer excitation energy to the metal centre. (C) 2007 Elsevier B.V. All rights reserved.