Delayed lanthanide luminescent Tb(III) complexes formed from lower rim amide functionalised calix[4]arenes

Abstract

The synthesis and the photophysical studies of a new generation of time resolved luminescent systems based on calix[4]arenes alkylated at the lower rim, capable of hosting lanthanide (III) ions such as terbium and sensitising its emission, are described. Two series of ligands were designed to provide an ideal cavity to host terbium (Tb(III)) and were synthesised in high yields following two novel approaches. The tetra-alkylation, which was achieved in one step using with piperidino- and morpholino-acetamide pendant arms, provides eight donor atoms forming a binding ‘pocket’ at an ideal distance from the metal core to favour the sensitisation via the antenna effect. Of the two ligand series developed, compounds 3 and 4 possess a short spacer between the calix and the amide receptor site. The second series of ligands 6–7, designed with longer pendant amide arms, was synthesised from 2 in two steps through the ester analogue 5. The crystal structure of 3 (and 6 as shown in Supporting Information, available online) is presented. The synthesis and the photophysical studies of the four resulting complexes 3.Tb, 4.Tb, 6.Tb and 7.Tb are described in detail and in each case, successful sensitisation of the terbium emission occurred upon excitation of the phenolic scaffold of the calixarene.

Abstract

The synthesis, X-ray crystal structure analysis of several calix[4]arene based ligands is described possessing amide functionalities at the lower rim of the macrocycle. Tb(III) complexes were formed from these ligands, which were characterised by NMR as well as HR-MS. The complexes were shown to be luminescent in solution, where the Tb(III) emission at long wavelength was monitored.

Keywords::

• supramolecular chemistry
• calix[4]arenes
• lanthanide
• terbium complexes
• solution studies
• luminescence

Notes

Present address: Christophe Lincheneau, Photochemical Nanosciences Laboratory, Dipartimento di Chimica “G. Ciamician”, Università di Bologna, Via Selmi 2, 40126 Bologna, Italy.^††Present address: Jonathan A. Kitchen, Department of Chemistry, Faculty of Natural & Environmental Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, UK.