葫芦[7]脲与紫精和香豆素修饰树枝形分子的分步结合及对体系发光性质的调控

Stepwise Assembly of CB[7] with Coumarin and Viologen Decorated Dendrimers and Regulation of Fluorescence Properties

合成了外围修饰香豆素PAMAM树枝形分子Gm-2（m＋1）C,外围和核心分别共价连接香豆素和紫精的树枝形分子EV-Gm-2（m＋1）C（m=0,1）,以及香豆素和紫精的模型化合物C-Model和EV,化合物均通过了1H NMR,IR和MALDI-TOF MS的鉴定.1H NMR和光物理研究结果表明,在p H=4.5的醋酸-醋酸钠缓冲溶液中,CB[7]与紫精和树枝形分子外围的香豆素基团均可形成1∶1的包结复合物,结合常数分别为3.3×10^6 mol^-1·L和1.4~1.6×10^5 mol^-1·L.香豆素基团中7位二乙氨基及取代侧部分香豆素环包裹在CB[7]刚性的疏水空腔内,包结复合物的形成限制了香豆素7位N,N＇-二乙氨基的扭转,抑制了香豆素基团从发光的分子内电荷转移（ICT）态向不发光的扭曲的分子内电荷转移（TICT）态的转变,而且CB[7]内腔的疏水环境有利于香豆素ICT态辐射跃迁,使体系发光大大增强.EV-Gm-2（m＋1）C与CB[7]的主客体作用为分步结合机制,加入的CB[7]先与紫精基团作用形成包结复合物,待体系中紫精基团与CB[7]结合后,体系中香豆素基团再与CB[7]作用形成包结复合物.无论是Gm-2（m＋1）C还是EV-Gm-2（m＋1）C体系,均可以通过加入CB[7]的量调节体系中香豆素基团与CB[7]形成包结复合物的多少,从而实现对Gm-2（m＋1）C和EV-Gm-2（m＋1）C体系发光的调控.本工作为可调控发光树枝形聚合物的发展提供了一种新的策略.

Host-guest system is one kind of supramolecular systems. Tremendous efforts have been devoted to develop new host-guest systems extending their applications in many research fields, such as molecular machine, drug delivery, chemsensor, and tuned emission materials. The cucurbit[n]uril family is a series of synthetic macrocyclic compounds, which has shown specific self-assembly properties such as high affinity, good selectivity, and high chemostability compared with the traditional supramolecular hosts, such as cyclodextrins, crown ethers, calixarenes, and many others. In the present work, a coumarin with 7-N,N＇-diethly substituent, an intramolecular charge transfer（ICT） based chromophore, was chosen as the fluorophore. The coumarin terminal-decorated polyamidoamine（PAMAM） dendrimers（Gm-2（m＋1）C, m=0, 1）, the coumarin and viologen-labled polyamidoamine dendrimers（EV-Gm-2（m＋1）C, m=0, 1） and the coumarin and viologen model compounds（C-Model and EV） were synthesized, their structures were characterized by 1H NMR, IR and MALDI-TOF mass spectrometry. EV and each terminal coumarin group of Gm-2（m＋1）C and EV-Gm-2（m＋1）C assembled with cucurbit[7]uril（CB[7]） forming 1∶1 inclusion complex with association constants of 3.3×10^6 mol^-1·L and 1.4×10^5~1.6×10^5 mol^-1·L. The 1H NMR study indicates that the 7-N,N＇-diethly moiety along with partial coumarin ring are encapsulated into the rigid hydrophobic cavity of CB[7] forming the inclusion complex of coumarin with CB[7]. The formation of the inclusion complex of coumarin with CB[7] restricts the rotation of the N,N＇-diethyl moiety, which suppresses the conversion from the emissive ICT excited state of coumarin to the nonemissive twisted intramolecular charge transfer（TICT） one, resulting in a dramatic increase of fluorescence emission. The hydrophobic microenvironment of the CB[7] cavity is also favorable to the ICT emission of coumarin. The interaction of CB[7] with EV-Gm-2（m＋1）C proceeds via a stepwise mechanism. CB[7] assembles with the viologen group first and starts to form inclusion complex with coumarin when the equivalent of CB[7] exceeds that of EV. The quantity of the inclusion complex of CB[7] with coumarin can be controlled by adjusting the adding amount of CB[7], consequently, regulating the fluorescence intensity of Gm-2（m＋1）C and EV-Gm-2（m＋1）C. This study provides a potential strategy for developing controllable light-emitting dendritic system with efficient synthesis.