Water-Soluble and Highly Luminescent Europium(III) Complexes with Favorable Photostability and Sensitive pH Response Behavior.
Two highly luminescent and water-soluble Eu(III) complexes, Eu1 and Eu2, based on novel carboxyl-functionalized 1,5-naphthyridine derivatives 8-hydroxy-1,5-naphthyridine-2-carboxylic acid (H2L1) and 7-cyano-8-hydroxy-1,5-naphthyridine-2-carboxylic acid (H2L2), respectively, are designed and synthesized. The crystal structure of Eu2 indicates that the central Eu(III) ion is nine-coordinated by three tridentate ligands (O^N^O). Both Eu1 and Eu2 show strong luminescence in aqueous solution with quantum yields (lifetimes) of 28% (1.1 ms) and 14% (0.76 ms), respectively. The chelates display unique UV-light stability in solution and remain highly emissive after 100 min of strong UV irradiation (∼300 W·m-2at 345 nm). Moreover, they exhibit reversible luminescence intensity changes with varied pH values, and the response mechanism is investigated. "Turn-on" of the Eu(III) emission upon increasing pH is realized by ligand structure change from keto to enol anion form, resulting in red-shifted absorption band and suppressed quenching from solvents and N-H vibration upon deprotonating. The results show that these novel Eu(III) complexes are quite intriguing for potential application as bioimaging agents and pH probes.
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Chen
C
Wei
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Huibo
H
Wei
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Weibo
W
Yan
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Zifeng
Z
Zhao
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Zelun
Z
Cai
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Boxun
B
Sun
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Zhaosha
Z
Meng
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Zhiwei
Z
Liu
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Zuqiang
Z
Bian
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China.
Chunhui
C
Huang
D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry / Q000528:radiation effects*; D005063:Europium / Q000737:chemistry / Q000528:radiation effects*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D049449:Luminescence; D009287:Naphthyridines / Q000138:chemical synthesis / Q000737:chemistry / Q000528:radiation effects*; D038761:Photobleaching; D012995:Solubility; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
D056831:Coordination Complexes; D008024:Ligands; D009287:Naphthyridines; D014867:Water; D005063:Europium