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Sensitized Emission of Luminescent Lanthanide Complexes Based on 4‐Naphthalen‐1‐yl‐Benzoic Acid Derivatives by a Charge‐Transfer Process
Author(s) -
Kim Yong Hee,
Baek Nam Seob,
Kim Hwan Kyu
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500291
Subject(s) - benzoic acid , chemistry , photoexcitation , lanthanide , luminescence , ligand (biochemistry) , photochemistry , intramolecular force , phosphorescence , fluorescence , excited state , ion , stereochemistry , organic chemistry , materials science , receptor , biochemistry , physics , optoelectronics , quantum mechanics , nuclear physics
The photophysical properties of 4‐naphthalen‐1‐yl‐benzoic acid ligands and their Eu III ‐cored complexes were systematically investigated to elucidate the effective energy‐transfer pathway in luminescent lanthanide complexes. A series of 4‐naphthalen‐1‐yl‐benzoic acid ligands, such as 4‐naphthalen‐1‐yl‐benzoic acid (NA‐1), 4‐[4‐(4‐methoxyphenyl)‐naphthalen‐1‐yl]‐benzoic acid (NA‐2), and 4‐{4‐[4‐(4‐methoxyphenyl)‐naphthalen‐1‐yl]‐benzyloxy}‐benzoic acid (NA‐3), were synthesized and utilized for the synthesis of their Eu III ‐cored complexes, corresponding to NAC‐1, NAC‐2, and NAC‐3. The fluorescence spectra of NA‐1 and NA‐2 show large Stokes shifts with increasing solvent polarity. These large Stokes shifts might be dominantly due to the formation of an intramolecular charge transfer (ICT) complex in the excited state. Also, the intensive luminescence of the Eu III ions by the photoexcitation of the ligand in NAC‐1 and NAC‐2 in polar solvents supports that the energy transfer from the ligand to the Eu III ion takes place efficiently. In the case of NA‐3, which has a CH 2 OPh group that acts as a blocking group, there is no dependence of the fluorescence spectrum on the solvent nature and no luminescence of the Eu III ions by the photoexcitation of the ligand, indicating no formation of the ICT state. This can be due to the fact that the formation of the ICT state in NA‐3 was prevented because the OCH 2 group acts as a blocking group by interrupting the π‐conjugation between the benzoic acid and the naphthalene unit. From these photophysical studies, we suggest that the ICT state plays a very important role in the energy‐transfer pathway from the ligand to the Eu III ion. To our best knowledge, this is the first demonstration of sensitized emission of luminescent lanthanide complexes based on 4‐naphthalen‐1‐yl‐benzoic acid derivatives by the charge‐transfer process.