Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, United Kingdom.
J Am Chem Soc. 2011 Dec 7;133(48):19442-7. doi: 10.1021/ja2067115. Epub 2011 Nov 10.
The different triplet sequences in high molecular weight aromatic copolyimides comprising pyromellitimide units ("I") flanked by either ether-ketone ("K") or ether-sulfone residues ("S") show different binding strengths for pyrene-based tweezer-molecules. Such molecules bind primarily to the diimide unit through complementary π-π-stacking and hydrogen bonding. However, as shown by the magnitudes of (1)H NMR complexation shifts and tweezer-polymer binding constants, the triplet "SIS" binds tweezer-molecules more strongly than "KIS" which in turn binds such molecules more strongly than "KIK". Computational models for tweezer-polymer binding, together with single-crystal X-ray analyses of tweezer-complexes with macrocyclic ether-imides, reveal that the variations in binding strength between the different triplet sequences arise from the different conformational preferences of aromatic rings at diarylketone and diarylsulfone linkages. These preferences determine whether or not chain-folding and secondary π-π-stacking occurs between the arms of the tweezer-molecule and the 4,4'-biphenylene units which flank the central diimide residue.
包含均苯二酰亚胺单元("I")的高分子量芳香族共聚酰亚胺的不同三联体序列，两侧为醚-酮("K")或醚-砜残基("S")，对基于芘的钳形分子表现出不同的结合强度。这些分子主要通过互补的π-π堆积和氢键与二酰亚胺单元结合。然而，正如（1）H NMR 络合位移和钳形聚合物结合常数的大小所示，三联体"SIS"比"KIS"更能结合钳形分子，而"KIS"又比"KIK"更能结合这种分子。钳形聚合物结合的计算模型，以及大环醚酰亚胺与钳形复合物的单晶 X 射线分析，揭示了不同三联体序列之间结合强度的变化源于二芳基酮和二芳基砜键合处芳环的不同构象偏好。这些偏好决定了钳形分子的臂与位于中心二酰亚胺残基两侧的 4,4'-联苯二酚单元之间是否发生链折叠和二级π-π堆积。
