Metal chelation-controlled twisted intramolecular charge transfer and its application to fluorescent sensing of metal ions and anions.
Two fluorescent ligands, N-(2-(5-cyanopyridyl))cyclen (L5) and N-(2-pyridyl)cyclen (L6) (cyclen = 1,4,7,10-tetraazacyclododecane), were designed and synthesized to control twisted intramolecular charge transfer (TICT) by metal chelation in aqueous solution. By complexation with Zn(2+), L6 exhibited TICT emissions at 430 nm (excitation at 270 nm) in 10 mM HEPES (pH 7.0) with I = 0.1 (NaNO(3)) at 25 degrees C due to the perpendicular conformation of a pyridine ring with respect to a dialkylamino group, which was fixed by Zn(2+)-N(pyridine) coordination, as proven by potentiometric pH, UV, and fluorescence titrations and X-ray crystal structure analysis. We further describe that the 1:1 complexation of ZnL6 with guests such as succinimide, phosphates, thiolates, and dicarboxylates, which compete with a nitrogen in the pyridine ring for Zn(2+) in ZnL6, induces considerable emission shift from TICT emissions (at 430 nm) to locally excited emissions (at ca. 350 nm) in neutral aqueous solution at 25 degrees C.
Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan. shinaoki@rs.noda.tus.ac.jp
Shin
S
Aoki
Daisuke
D
Kagata
Motoo
M
Shiro
Kei
K
Takeda
Eiichi
E
Kimura