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Self‐Assembled Triple‐Stranded Lanthanide Dimetallic Helicates with a Ditopic Ligand Derived from Bis(benzimidazole)pyridine and Featuring an (4‐Isothiocyanatophenyl)ethynyl Substituent
Author(s) -
Tripier Raphaël,
Hollenstein Marcel,
Elhabiri Mourad,
Chauvin AnneSophie,
Zucchi Gaël,
Piguet Claude,
Bünzli JeanClaude G.
Publication year - 2002
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(200207)85:7<1915::aid-hlca1915>3.0.co;2-n
Subject(s) - chemistry , lanthanide , substituent , pyridine , ligand (biochemistry) , quantum yield , luminescence , crystallography , acetonitrile , singlet state , stereochemistry , ring (chemistry) , excited state , fluorescence , ion , medicinal chemistry , organic chemistry , biochemistry , physics , receptor , optoelectronics , quantum mechanics , nuclear physics
Bis(2‐{6‐(diethylcarbamoyl)‐4‐[(4‐isothiocyanatophenyl)ethynyl]pyridin‐2′‐yl}‐1‐ethylbenzimidazol‐5‐yl)methane ( L G ) reacts with trivalent lanthanide ions in acetonitrile to yield triple‐stranded dimetallic helicates [Ln 2 ( L G ) 3 ] 6+ . 1 H‐NMR Data point to the helicates being the only species formed under stoichiometric conditions and having a time‐averaged D 3 symmetry on the NMR time scale. The photophysical properties of L G and its helicates are discussed with respect to the closely related ligands L B , L E , and their complexes, two ligands devoid of the isothiocyanatophenylethynyl substituent. The quantum yield of the ligand fluorescence is three times smaller compared to L E , while that of the Eu III ‐centered luminescence (1.1%) is three times larger. On the other hand, the luminescence of Tb III is not sensitized by L G . This is explained in terms of energy differences between the singlet and triplet states on one hand, and between the 0‐phonon transition of the triplet state and the excited metal ion states on the other. This work demonstrates that bulky substituents in the 4‐position of the pyridine ring do not prevent the formation of triple‐stranded helicates, opening the way for luminescent probes that can easily be coupled to biological materials.