Samanta Samaresh, Raval Parth, Manjunatha Reddy G N, Chaudhuri Debangshu
Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur 741246, India.
Univ. Lille, CNRS, Centrale Lille Institut, Univ. Artois, UMR 8181, Unité de Catalyse et Chimie du Solide, F-59000 Lille, France.
ACS Cent Sci. 2021 Aug 25;7(8):1391-1399. doi: 10.1021/acscentsci.1c00604. Epub 2021 Jul 22.
Cooperative interactions play a pivotal role in programmable supramolecular assembly. Emerging from a complex interplay of multiple noncovalent interactions, achieving cooperativity has largely relied on empirical knowledge. Its development as a rational design tool in molecular self-assembly requires a detailed characterization of the underlying interactions, which has hitherto been a challenge for assemblies that lack long-range order. We employ extensive one- and two-dimensional magic-angle-spinning (MAS) solid-state NMR spectroscopy to elucidate key structure-directing interactions in cooperatively bound aggregates of a perylene bisimide (PBI) chromophore. Analysis of H-C cross-polarization heteronuclear correlation (CP-HETCOR) and H-H double-quantum single-quantum (DQ-SQ) correlation spectra allow the identification of through-space H···C and H···H proximities in the assembled state and reveals the nature of molecular organization in the solid aggregates. Emergence of cooperativity from the synergistic interaction between a stronger π-stacking and a weaker interstack hydrogen-bonding is elucidated. Finally, using a combination of optical absorption, circular dichroism, and high-resolution MAS NMR spectroscopy based titration experiments, we investigate the anomalous solvent-induced disassembly of aggregates. Our results highlight the disparity between two well-established approaches of characterizing cooperativity, using thermal and good solvent-induced disassembly. The anomaly is explained by elucidating the difference between two disassembly pathways.
协同相互作用在可编程超分子组装中起着关键作用。协同作用源于多种非共价相互作用的复杂相互影响，其实现很大程度上依赖于经验知识。作为分子自组装中的一种合理设计工具，其发展需要对潜在相互作用进行详细表征，而对于缺乏长程有序性的组装体而言，这一直是一项挑战。我们采用广泛的一维和二维魔角旋转（MAS）固态核磁共振光谱来阐明苝二酰亚胺（PBI）发色团协同结合聚集体中的关键结构导向相互作用。对H-C交叉极化异核相关（CP-HETCOR）和H-H双量子单量子（DQ-SQ）相关光谱的分析，能够识别组装状态下的空间H···C和H···H接近度，并揭示固体聚集体中的分子组织性质。阐明了较强的π堆积和较弱的层间氢键之间的协同相互作用所产生的协同性。最后，结合光吸收、圆二色性和基于高分辨率MAS NMR光谱的滴定实验，我们研究了聚集体异常的溶剂诱导解聚。我们的结果突出了两种成熟的表征协同性方法（利用热解聚和良溶剂诱导解聚）之间的差异。通过阐明两种解聚途径之间的差异来解释这种异常现象。
