Wang Zhiping, Chang S H, Kang T J
Department of Chemistry, Daegu University, Gyeongsan 712-714, Republic of Korea.
Spectrochim Acta A Mol Biomol Spectrosc. 2008 Jul;70(2):313-7. doi: 10.1016/j.saa.2007.08.006. Epub 2007 Aug 17.
Pyrene- and anthracene-appended new crown ether derivatives have been synthesized by Schiff's base reaction, and cation complexation behavior was investigated by fluorescence spectroscopy measurements. Based on photo-induced electron transfer and intramolecular charge transfer mechanism, the host molecules emit stronger fluorescence in the presence of various cations Na(+), K(+), Rb(+), Cs(+) and NH(4)(+) since the complexation between guest cations and crown ether compounds inhibit partial electron transfer from the nitrogen atom to the chromophores and subsequently fluorescence is enhanced. The binding constants were estimated from the plots of the fraction of binding sites filled for crown ether compound as a function of free-ion concentration. Results show that 15-crown-5 derivatives exhibit higher binding ability with sodium cations while 18-crown-6 derivatives had higher affinity for potassium cations, which is consistent with the hole-size relationship of the crown ethers. Ammonium ion complexation caused largest fluorescence enhancement. It is understood that ammonium ion cannot only complex with crown ether, but also interact directly with the lone pair electrons of nitrogen atom in C=N bond so that electron transfer from the nitrogen atom to chromophores is further inhibited.
通过席夫碱反应合成了芘和蒽连接的新型冠醚衍生物，并通过荧光光谱测量研究了阳离子络合行为。基于光诱导电子转移和分子内电荷转移机制，由于客体阳离子与冠醚化合物之间的络合抑制了从氮原子到发色团的部分电子转移，随后荧光增强，主体分子在各种阳离子Na(+)、K(+)、Rb(+)、Cs(+)和NH4(+)存在下发出更强的荧光。结合常数是根据冠醚化合物填充的结合位点分数与自由离子浓度的函数关系图估算的。结果表明，15-冠-5衍生物对钠离子表现出更高的结合能力，而18-冠-6衍生物对钾离子具有更高的亲和力，这与冠醚的孔径关系一致。铵离子络合导致最大的荧光增强。据了解，铵离子不仅能与冠醚络合，还能直接与C=N键中氮原子的孤对电子相互作用，从而进一步抑制从氮原子到发色团的电子转移。
