Solvent Dependent Fluorescent Properties of a 1,2,3-Triazole Linked 8-Hydroxyquinoline Chemosensor: Tunable Detection from Zinc(II) to Iron(III) in the CH3CN/H2O System

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• 作者：Erhong Hao ; Ting Meng ; Min Zhang ; Weidong Pang ; Yunyou Zhou ; Lijuan Jiao
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：July 28, 2011
• 年：2011
• 卷：115
• 期：29
• 页码：8234-8241
• 全文大小：1041K
• 年卷期：v.115,no.29(July 28, 2011)
• ISSN：1520-5215

文摘

A triazole-containing 8-hydroxyquinoline (8-HQ) ether 2 was efficiently synthesized in two steps from the 鈥渃lick鈥?strategy. Compound 2 gave a strong fluorescence (桅 = 0.21) in nonprotic solvent like CH₃CN, and a weak fluorescence (桅 = 0.06) in protic solvent like water. In water, a more than 100 nm red shift of the fluorescence maximum was observed for compound 2 in comparison with that in CH₃CN. This fluorescence difference may be attributed to the intermolecular photoinduced proton transfer (PPT) process involving the protic solvent water molecules. Similarly, this intermolecular PPT process was also observed in the high-water-content CH₃CN aqueous solution (e.g., CH₃CN/H₂O = 5/95, v/v). The water content in the CH₃CN/H₂O binary solvent mixture greatly affected the fluorescence intensity (e.g., 桅 = 0.06 and 0.25 when CH₃CN/H₂O = 5/95 and 95/5, v/v, respectively) and emission wavelength. Using this interesting property, by simple variation of the water content in the CH₃CN aqueous solution, compound 2 was tuned from a selective 鈥渢urn-on鈥?fluorescent sensor for Zn²⁺ (CH₃CN/H₂O = 5/95, v/v) to a ratiometric one for Zn²⁺ and a selective 鈥渢urn-off鈥?one for Fe³⁺ (CH₃CN/H₂O = 95/5, v/v) over a wide range of pH value. In high-water-content (CH₃CN/H₂O = 5/95, v/v) aqueous solution compound 2 shows a selective 鈥渢urn-on鈥?response toward Zn²⁺, with a 10-fold enhancement in the fluorescence intensity at 428 nm and a 62 nm blue shift of the emission maximum (490 to 428 nm) due to the inhibition of intermolecular PPT process upon chelating with Zn²⁺. However, in a less polar solvent (CH₃CN/H₂O = 95/5, v/v) in which compound 2 has high fluorescence (quantum yield =0.25), it shows a ratiometric response toward Zn²⁺, with a continuous decrease of the fluorescence intensity at 399 nm and an increase at 423 nm. More interestingly, in this case, it also exhibits a very sensitive, selective, and ratiometric fluorescence quenching in the presence of Fe³⁺, with an 81 nm red shift of the emission maximum (399 to 480 nm) in a wide range of pH through a metal ligand charge transfer (MLCT) effect.