Anhui Key Laboratory of Functional Molecular Solids, College of Chemistry and Material Science, Anhui Normal University, Wuhu 241000, China.
J Phys Chem A. 2011 Jul 28;115(29):8234-41. doi: 10.1021/jp202700s. Epub 2011 Jul 6.
A triazole-containing 8-hydroxyquinoline (8-HQ) ether 2 was efficiently synthesized in two steps from the "click" strategy. Compound 2 gave a strong fluorescence (Φ = 0.21) in nonprotic solvent like CH(3)CN, and a weak fluorescence (Φ = 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 CH(3)CN. 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 CH(3)CN aqueous solution (e.g., CH(3)CN/H(2)O = 5/95, v/v). The water content in the CH(3)CN/H(2)O binary solvent mixture greatly affected the fluorescence intensity (e.g., Φ = 0.06 and 0.25 when CH(3)CN/H(2)O = 5/95 and 95/5, v/v, respectively) and emission wavelength. Using this interesting property, by simple variation of the water content in the CH(3)CN aqueous solution, compound 2 was tuned from a selective "turn-on" fluorescent sensor for Zn(2+) (CH(3)CN/H(2)O = 5/95, v/v) to a ratiometric one for Zn(2+) and a selective "turn-off" one for Fe(3+) (CH(3)CN/H(2)O = 95/5, v/v) over a wide range of pH value. In high-water-content (CH(3)CN/H(2)O = 5/95, v/v) aqueous solution compound 2 shows a selective "turn-on" response toward Zn(2+), 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 Zn(2+). However, in a less polar solvent (CH(3)CN/H(2)O = 95/5, v/v) in which compound 2 has high fluorescence (quantum yield =0.25), it shows a ratiometric response toward Zn(2+), 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 Fe(3+), 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.
一种含三唑的 8-羟基喹啉（8-HQ）醚 2 通过“点击”策略从两步法高效合成。化合物 2 在非质子溶剂如 CH(3)CN 中表现出强荧光（Φ=0.21），在质子溶剂如水相中表现出弱荧光（Φ=0.06）。在水中，与在 CH(3)CN 中相比，化合物 2 的荧光最大波长发生了超过 100nm 的红移。这种荧光差异可能归因于涉及质子溶剂水分子的分子间光致质子转移（PPT）过程。同样，在高含水量的 CH(3)CN 水溶液中（例如，CH(3)CN/H(2)O=5/95，v/v）也观察到了这种分子间 PPT 过程。CH(3)CN/H(2)O 二元溶剂混合物中的含水量极大地影响了荧光强度（例如，当 CH(3)CN/H(2)O 分别为 5/95 和 95/5，v/v 时，Φ 分别为 0.06 和 0.25）和发射波长。利用这一有趣的性质，通过简单改变 CH(3)CN 水溶液中的含水量，化合物 2 从 Zn(2+)的选择性“开启”荧光传感器（CH(3)CN/H(2)O=5/95，v/v）调谐为 Zn(2+)的比率型传感器和 Fe(3+)的选择性“关闭”传感器，在很宽的 pH 值范围内。在高含水量（CH(3)CN/H(2)O=5/95，v/v）水溶液中，化合物 2 对 Zn(2+)表现出选择性的“开启”响应，在 428nm 处荧光强度增强了 10 倍，发射最大值（490 至 428nm）蓝移了 62nm，这是由于与 Zn(2+)螯合后抑制了分子间 PPT 过程。然而，在极性较低的溶剂（CH(3)CN/H(2)O=95/5，v/v）中，化合物 2 具有高荧光（量子产率=0.25），它对 Zn(2+)表现出比率型响应，在 399nm 处的荧光强度连续降低，在 423nm 处增加。更有趣的是，在这种情况下，它还在很宽的 pH 值范围内通过金属配体电荷转移（MLCT）效应，对 Fe(3+)表现出非常灵敏、选择性和比率型荧光猝灭，发射最大值（399nm 至 480nm）红移了 81nm。
