期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：18
页码：5597-5601
DOI：10.1073/pnas.1500489112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceIn this study, the preparation of organometallic rotaxane dendrimers with a well-defined topological structure and enhanced rigidity was developed. Starting from a simple rotaxane building block, high-generation rotaxane branched dendrimers were synthesized and characterized. The fourth-generation structure described is among the highest-generation organometallic rotaxane dendrimers reported to date. The introduction of pillar[5]arene rotaxane units activates dynamic features in the dendrimer and enhances the rigidity of each branch of the supermolecules. This research offers a facile approach to the construction of high-generation rotaxane branched dendrimer, which not only enriches the library of rotaxne dendrimer but also provides the further insight into their applications as supramolecular dynamic materials. Mechanically interlocked molecules, such as catenanes, rotaxanes, and knots, have applications in information storage, switching devices, and chemical catalysis. Rotaxanes are dumbbell-shaped molecules that are threaded through a large ring, and the relative motion of the two components along each other can respond to external stimuli. Multiple rotaxane units can amplify responsiveness, and repetitively branched molecules--dendrimers--can serve as vehicles for assembly of many rotaxanes on single, monodisperse compounds. Here, we report the synthesis of higher-generation rotaxane dendrimers by a divergent approach. Linkages were introduced as spacer elements to reduce crowding and to facilitate rotaxane motion, even at the congested periphery of the compounds up to the fourth generation. The structures were characterized by 1D multinuclear (1H, 13C, and 31P) and 2D NMR spectroscopy, MALDI-TOF-MS, gel permeation chromatography (GPC), and microscopy-based methods including atomic force microscopy (AFM) and transmission electron microscopy (TEM). AFM and TEM studies of rotaxane dendrimers vs. model dendrimers show that the rotaxane units enhance the rigidity and reduce the tendency of these assemblies to collapse by self-folding. Surface functionalization of the dendrimers with ferrocenes as termini produced electrochemically active assemblies. The preparation of dendrimers with a well-defined topological structure, enhanced rigidity, and diverse functional groups opens previously unidentified avenues for the application of these materials in molecular electronics and materials science.
