Calix[4]azacrowns as novel molecular scaffolds for the generation of visible and near-infrared lanthanide luminescence

• Type: Article in International Scientific Journal
• Date: 2006

Authors

Oueslati, I (Author) Other; Ferreira, RAS (Author) Other; Carlos, LD (Author) Other; Baleizao, C (Author) Other; Berberan Santos, MN (Author) Other; de Castro, B (Author) FCUP; Vicens, J (Author) Other; Pischel, U (Author) Other

Journal

Title: Inorganic Chemistry

Vol. 45

Pages: 2652-2660

ISSN: 0020-1669

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 49 Citations

Scopus - 53 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-004-MQ8

DOI: 10.1021/ic051159l

Abstract (EN): Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation of lanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, and stability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally on the order of log beta(11) approximate to 5-6 and log beta(12) approximate to 10. The structural changes of the ligands upon La(Ill) complexation were probed by (1)H NMR spectroscopy. The two ligands were observed to have opposite fluorescence behaviors, namely, fluorescence enhancement (via blocking of photoinduced electron transfer from amine groups) or quenching (via lanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence was sensitized by excitation in the pi,pi* band of the aromatic moieties of the ligands. The direct involvement of the antenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(Ill). Generally, Eu(III) luminescence was weak ((Phi(lum) <= 0.01%) and much shorter lived (tau(lum) = 0.36 ms) than the Tb(111) emission. The latter, on the other hand, reached lifetimes of up to 2.60 ms and quantum yields as high as 12% for one of the ligands. Water/deuterium oxide exchange experiments showed the presence of only one solvent molecule in the coordination sphere of the lanthanides. However, Eu(III) luminescence was efficiently quenched by NH oscillators and the presence of a ligand-to-metal charge transfer state. Near-infrared luminescence of Nd(III) was also generated by energy-transfer sensitization.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 9