Wang Ruyu, Shu Xi, Fan Yu, Li Shoujian, Jin Yongdong, Huang Chao
College of Chemistry, Sichuan University No. 29 Wangjiang Road Chengdu 610064 Sichuan PR China
RSC Adv. 2018 Nov 26;8(69):39394-39407. doi: 10.1039/c8ra07495j. eCollection 2018 Nov 23.
A series of asymmetric tris-urea receptors with electron withdrawing group (EWG) or electron donating group (EDG), L1-L4, were synthesized and characterized by high resolution mass spectroscopy (HRMS), nuclear magnetic resonance spectroscopy (NMR) and single-crystal X-ray diffraction (XRD) techniques. Receptors with EWG substituent showed different visible colorimetric response to fluoride and hydroxide anions. Binding studies toward various monovalent anions were performed by UV-Vis and NMR titration experiments. The experimental results revealed that these tris-urea receptors underwent stepwise deprotonation of the three N-H protons in the presence of varying excess of fluoride and hydroxide anions. This phenomenon was signalled by the development of vivid colours. These findings were also supported by density functional theory (DFT) and time-dependent DFT (TDDFT) theoretical calculations. DFT studies proved that the deprotonation of receptors with EWG substituent was energetically favourable in comparison with the receptor containing EDG substituent. TDDFT calculations for molecular orbital distribution, oscillator strength, and the electron transition process between the ground state and excited state of receptors and their corresponding deprotonated receptors were performed to elucidate the different absorption properties.
合成了一系列带有吸电子基团（EWG）或供电子基团（EDG）的不对称三脲受体L1-L4，并通过高分辨率质谱（HRMS）、核磁共振光谱（NMR）和单晶X射线衍射（XRD）技术对其进行了表征。带有EWG取代基的受体对氟离子和氢氧根阴离子表现出不同的可见比色响应。通过紫外可见光谱和核磁共振滴定实验对各种单价阴离子进行了结合研究。实验结果表明，在不同过量的氟离子和氢氧根阴离子存在下，这些三脲受体的三个N-H质子会逐步去质子化。这种现象通过鲜明颜色的出现得以体现。这些发现也得到了密度泛函理论（DFT）和含时密度泛函理论（TDDFT）理论计算的支持。DFT研究证明，与含有EDG取代基的受体相比，带有EWG取代基的受体去质子化在能量上更有利。进行了TDDFT计算，以研究受体及其相应去质子化受体的分子轨道分布、振子强度以及基态和激发态之间的电子跃迁过程，从而阐明不同的吸收特性。
