Radboud University Nijmegen, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
Phys Chem Chem Phys. 2011 Jul 28;13(28):13082-95. doi: 10.1039/c1cp20304e. Epub 2011 Jun 15.
Carbazole functionalized polyisocyanides are known to exhibit excellent electronic properties (E. Schwartz, et al., Chemistry of Materials, 2010, 22, 2597). The functionalities and properties of such materials crucially depend on the organization and stability of the polymer structure. We combine solid-state Nuclear Magnetic Resonance (NMR) experiments with first-principles calculations of isotropic chemical shifts, within the recently developed converse approach, to rationalize the origin of isotropic chemical shifts in the crystalline monomer l-isocyanoalanine 2-(9H-carbazol-9-yl) ethyl amide (monomer 1) and thereby gain insight into the structural organization of its polymer (polymer 2). The use of state-of-the-art solid-state NMR experiments combined with Density Functional Theory (DFT) based calculations allows an unambiguous assignment of all proton and carbon resonances of the monomer. We were able to identify the structure stabilising interactions in the crystal and understand the influence of the molecular packing in the crystal structure on the chemical shift data observed in the NMR spectra. Here the Nuclear Independent Chemical Shift (NICS) approach allows discriminating between 'physical' interactions amongst neighboring molecules such as ring-current effects and 'chemical' interactions such as hydrogen bonding. This analysis reveals that the isocyanide monomer is stabilized by multiple hydrogen bonds such as a bifurcated hydrogen bond involving -N-H, -C-H and O=C- moieties and Ar-H···C≡N- hydrogen bonding (Ar = aromatic group). Based on the geometrical arrangement it is postulated that the carbazole units are involved in the weak σ-π interactions giving rise to a Herringbone packing of the molecules. The chemical shift analysis of the polymer spectra readily establishes the existence of N-H···O=C hydrogen bonds despite the limited resolution exhibited by the polymer spectra. It is also elucidated that the relative arrangement of the carbazole units in the polymer differs significantly from that of the monomer.
咔唑功能化聚异氰化物以具有优异的电子性质而闻名（E. Schwartz 等人，《化学材料》，2010 年，22，2597）。此类材料的功能和性质主要取决于聚合物结构的组织和稳定性。我们结合固态核磁共振（NMR）实验和各向同性化学位移的第一性原理计算，在最近发展的逆方法中，对晶体单体 l-异氰酸基丙氨酸 2-(9H-咔唑-9-基)乙基酰胺（单体 1）中各向同性化学位移的起源进行了合理化，并深入了解其聚合物（聚合物 2）的结构组织。使用最先进的固态 NMR 实验与基于密度泛函理论（DFT）的计算相结合，可以对单体的所有质子和碳共振进行明确的分配。我们能够确定晶体中的结构稳定相互作用，并了解分子堆积在晶体结构中对 NMR 光谱中观察到的化学位移数据的影响。在这里，核独立化学位移（NICS）方法可以区分相邻分子之间的“物理”相互作用，例如环电流效应和“化学”相互作用，例如氢键。该分析表明，异氰化物单体通过多个氢键稳定，例如涉及-N-H、-C-H 和 O=C-部分的分叉氢键和 Ar-H···C≡N-氢键（Ar = 芳基）。基于几何排列，推测咔唑单元参与了弱 σ-π 相互作用，导致分子的鱼骨状堆积。聚合物光谱的化学位移分析很容易确定 N-H···O=C 氢键的存在，尽管聚合物光谱的分辨率有限。还阐明了聚合物中咔唑单元的相对排列与单体显著不同。
