Synthetic Metals 159 (2009) 356–360 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Synthesis of 8-hydroxyquinoline functionalised DO3A ligand and Eu(III) and Er(III) complexes: Luminescence properties Fabio Rizzo a , Francesco Meinardi b , Riccardo Tubino b , Roberto Pagliarin c , Giovanna Dellepiane a , Antonio Papagni b,∗ a INSTM and Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso 31, I-16146 Genova, Italy b Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 53, I-20125 Milano, Italy c Dipartimento di Chimica Organica e Industriale, Università di Milano, Viale Venezian 21, I-20133 Milano, Italy article info Article history: Received 7 August 2007 Accepted 1 November 2007 Available online 28 March 2009 Keywords: Lanthanides Luminescence Energy transfer Macrocycles Supramolecular chemistry abstract The synthesis of a new DO3A-based macrocyclic ligand bearing a 8-hydroxyquinoline residue together with the preparation of its Eu 3+ and Er 3+ neutral complexes are described. In a previous report [F. Rizzo, A. Papagni, F. Meinardi, R. Tubino, M. Ottonelli, G.F. Musso, G. Dellepiane, Synth. Met. 147 (2004) 143], we have shown that lanthanide complexes display very high stability combined with a good luminescence in aqueous solution under UV radiation, which indicate an energy transfer process from the excited 8- hydroxyquinoline moiety to the metal. In this work, we correlate the ability to transfer the energy from the sensitizer to lanthanide ion with pH behaviour of the antenna. Furthermore, the variation of pH in Eu 3+ complex supports the hypothesis of presence of charge-transfer transitions. The good solubility and sensitized emission in different solvents (organic and water) are very important aspects for their technologic applications as luminescent probes or NIR-emitting devices. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Because of the efficient resonant energy transfer from the light harvesting antenna to the ion, the lanthanide complexes of organic ligands often show excellent luminescence characteristics that make them very appealing and promising materials for optoelec- tronic applications. As an example, the extremely sharp lanthanide emission bands in the visible combined with high luminous inten- sity can be exploited in developing new organic based displays [2], while the long lifetime of excited state observed in many lan- thanides and the possibility of obtaining IR emission (by using Er 3+ , Nd 3+ and Yb 3+ ) are useful in the telecommunication field [3]. In these complexes the problem of direct excitation into the sharp and very weak (forbidden) absorption bands of the lanthanide ion is circumvented by indirect pumping into the strong singlet–singlet absorption band of the ligand, called “antenna effect” [4]. Fur- thermore, high kinetic stability and solubility in aqueous solution shown by some of these complexes have recently opened to the pos- sibility of exploiting them for biological applications, as biological probes and contrast agents for MRI technique [5]. Among the large numbers of ligands synthesised and employed to complex rare earth metals, the 1,4,7,10-tetraazacyclododecane- 1,4,7-triacetic acid (DO3A)-based ligands offer many advantages: ∗ Corresponding author. Tel.: +39 02 64485234; fax: +39 02 64485400. E-mail address: antonio.papagni@unimib.it (A. Papagni). this macrocyclic ligand engages seven (four nitrogen atom and three carboxylic groups) of nine coordination sites of the metal, thus fabricating a cage around the lanthanide ion which enormously increases the stability of complex (k stab. usually over 10 20 ); the com- plexes are neutral and this increases the solubility also in organic solvents; the non-substituted nitrogen atoms can be exploited to anchor the antenna. This latter can be coordinated by the metal using the remaining free sites. The use of suitable antenna can completely saturate the coordination sphere of the metal and the coordination of small molecules such as water inhibited. The latter aspect holds an important role in reducing the quenching of the infra-red emission due by vibrational coupling with O–H oscilla- tors of the coordinated water molecules or of other O–H containing molecules. Following this approach, the synthesis of DO3A-based lig- and bearing phenantroline [6–8], acridone [9] or aromatic sulphonamide [10] antennas and the optical properties of their complexes with lanthanide has been already reported. Herein, we report on the synthesis and the optical characteri- zation of a DO3A-based ligand (1) bearing an 8-hydroxyquinoline residue as antenna and the corresponding lanthanide complexes of which we already reported preliminary analysis [1]. This antenna has been chosen since it provides an efficient intramolecular energy transfer from its lowest triplet state to the ion as investigated in other lanthanide complexes [11,12]. Furthermore the erbium tris- hydroxyquinolinate is a well known complex [13], often used as reference standard for comparing the emission efficiency of oth- 0379-6779/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2007.11.013