Dirksen Anouk, Hahn Uwe, Schwanke Frank, Nieger Martin, Reek Joost N H, Vögtle Fritz, De Cola Luisa
Institute of Molecular Chemistry, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
Chemistry. 2004 Apr 19;10(8):2036-47. doi: 10.1002/chem.200305461.
The well-known unsubstituted "Hamilton receptor" was monofunctionalized with an amino group and attached at the periphery of poly(propyleneamine) dendrimers through the use of an activated ester. Four generations of Hamilton-receptor-functionalized dendrimers (HR-dendrimers) were synthesized and characterized by (1)H and (13)C NMR spectroscopy and MALDI-TOF mass spectrometry. The photophysical properties of the HR-dendrimers were investigated by UV/Vis as well as with steady-state and time-resolved fluorescence spectroscopy. The dendrimers were used as multivalent hosts for the barbiturate guests Barbital (7) and [Re(Br)(CO)(3)(barbi-bpy)] (8; barbi-bpy=5-[4-(4'-methyl)-2,2'-bipyridyl]methyl-2,4,6-(1 H,3 H,5 H)-pyrimidinetrione). The stable adducts formed between the dendritic architectures (the hosts) and the barbiturate guests 7 and 8 were investigated by (1)H NMR spectroscopy and photophysical methods. The binding constants of the barbiturate guests for binding to reference compound 2 (with a single receptor unit) in chloroform were found to be 1.4 x 10(3) M(-1) and 1.5 x 10(5) M(-1) for 7 and 8, respectively. Binding of 7 to the dendrimers enhances the weak emission of the Hamilton receptor. This increase in emission is also generation dependent; it was found to be most pronounced in the case of 2 and the least in the case of the fourth-generation dendrimer 6. The unexpected increase in the quantum yield of emission from the HR-dendrimers with increasing generation could be caused by the rather rigid conformation of the Hamilton receptors in later-generation compounds, which is a result of intramolecular aggregation and steric hindrance at the periphery of the dendrimer. The photoinduced energy transfer from the excited state of the HR-dendrimers to the lower-lying excited state of the guest 8 was used to probe the formation of host-guest complexes. The rate of energy transfer was calculated to be 3.6 x 10(10) s(-1). Energy transfer in 2 subset 8 only occurred in the presence of a strong base, which shows that the basic amine core in the HR-dendrimers is crucial for this photoinduced process. The binding of 8 to the dendrimers is completely reversible: 8 can be exchanged with a competitive guest such as 7 and the emission of the HR-dendrimer is restored.
著名的未取代“汉密尔顿受体”用氨基进行单官能化，并通过活化酯连接在聚（丙胺）树枝状大分子的外围。合成了四代汉密尔顿受体功能化树枝状大分子（HR-树枝状大分子），并通过¹H和¹³C NMR光谱以及基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）进行表征。通过紫外可见光谱以及稳态和时间分辨荧光光谱研究了HR-树枝状大分子的光物理性质。这些树枝状大分子用作巴比妥酸盐客体巴比妥（7）和[Re(Br)(CO)₃(barbi-bpy)]（8；barbi-bpy = 5-[4-(4'-甲基)-2,2'-联吡啶]甲基-2,4,6-(1H,3H,5H)-嘧啶三酮）的多价主体。通过¹H NMR光谱和光物理方法研究了树枝状结构（主体）与巴比妥酸盐客体7和8之间形成的稳定加合物。发现巴比妥酸盐客体在氯仿中与参考化合物2（具有单个受体单元）结合的结合常数，对于7和8分别为1.4×10³ M⁻¹和1.5×10⁵ M⁻¹。7与树枝状大分子的结合增强了汉密尔顿受体的微弱发射。这种发射增加也与代数有关；发现对于第二代树枝状大分子2最为明显，而对于第四代树枝状大分子6最不明显。随着代数增加，HR-树枝状大分子发射量子产率意外增加可能是由于后期化合物中汉密尔顿受体相当刚性的构象，这是树枝状大分子外围分子内聚集和空间位阻的结果。利用从HR-树枝状大分子的激发态到客体8的较低激发态的光诱导能量转移来探测主体-客体复合物的形成。计算得出能量转移速率为3.6×10¹⁰ s⁻¹。2与8之间的能量转移仅在强碱存在下发生，这表明HR-树枝状大分子中的碱性胺核对于此光诱导过程至关重要。8与树枝状大分子的结合是完全可逆的：8可以与竞争性客体如7交换，并且HR-树枝状大分子的发射得以恢复。
