Synthesis of Functionalized Calix[4]arene Ligands Incorporating Bipyridine N,N-Dioxide Chromophores and Luminescence of Their Lanthanide Complexes

Abstract

Luminescence spectroscopy is attracting immense interest quired characteristics have been synthesized, [6] and, among these, particular attention has been focused on funcin the scientific community owing to its potential application in growing fields of great economical and social im-tionalized calixarenes.[ ResultsThe major drawback in photoluminescence analysis, particularly when dealing with biological material, is the interLigands 1 and 2 and their lanthanide complexes were prepared as outlined in Schemes 1 and 2 using well-estabference caused by autofluorescence and light scattering. Time resolved spectroscopy, which requires the use of labels lished synthetic procedures for 1,3-disubstituted calix[4]arene ethers in the cone conformation. [20] [21] The initially dewith very long luminescence lifetimes, can efficiently exclude this kind of background light. For this reason, over signed ligand 1 was prepared by reaction of p-tert-butylcalix[4]arene with 5-bromomethyl-5Ј-methyl-2,2Ј-bipyridine the past decade great interest has been centered on the design of luminescent complexes containing the Eu 3ϩ and N,NЈ-dioxide in anhydrous acetonitrile using K 2 CO 3 as base (Scheme 1). Ligand 2 (Scheme 2) was prepared under Tb 3ϩ ions, which possess luminescence lifetimes in the micro-to millisecond range.[To obtain an ef-similar conditions starting from p-tert-butylcalix [4]arene and 5,5Ј-bromomethyl-2,2Ј-bipyridine N,NЈ-dioxide. Both ficient luminescent label, the ligand needs to be able to form stable complexes with the lanthanide ions in coordinating ligands were isolated in a pure state after chromatography on neutral alumina. In solution at room temperature, they solvents, to shield the ion from deactivating solvent molecules, and, particularly importantly, to absorb light and adopt a fixed cone conformation with the ligating groups on the same side of the plane formed by the macrocycle, as to transfer it to the metal ion with high efficiency, thereby overcoming the intrinsic low absorption coefficients of the was deduced from their 1 H-NMR spectra. In both ligands, the methylene protons give rise to an AB quadruplet, at δ ϭ metal ions.[6] [7] [8] [9] With these goals in mind, and thanks to the great progress made in the field of supramolecular 3.75 (J AB ϭ 13.1 Hz and ∆ν ϭ 168.5 Hz) in 1 and at δ ϭ 3.81 (J AB ϭ 13.3 Hz and ∆ν ϭ 172.2 Hz) in 2. The aromatic chemistry, many encapsulating ligands possessing the reEur.