Oliveras-González Cristina, Linares Mathieu, Amabilino David B, Avarvari Narcis
MOLTECH-Anjou, UMR 6200, CNRS, Univ. Angers, 2bd Lavoisier, 49045 Angers Cedex, France.
Laboratory of Organic Electronics, ITN, Campus Norrköping, Scientific Visualization Group, ITN, Campus Norrköping, and Swedish e-Science Research Centre (SeRC), Linköping University, SE-581 83 Linköping, Sweden.
ACS Omega. 2019 Jun 11;4(6):10108-10120. doi: 10.1021/acsomega.9b01050. eCollection 2019 Jun 30.
Weak noncovalent interactions between large disclike molecules in poorly solvating media generally lead to the formation of fibers where the molecules stack atop one another. Here, we show that a particular chiral spacing group between large aromatic moieties, which usually lead to columnar stacks, in this case gives rise to an intramolecularly folded structure in relatively polar solvents, but in very apolar solvents forms finite aggregates. The molecule that displays this behavior has a symmetric benzene-1,3,5-tris(3,3'-diamido-2,2'-bipyridine) (BTAB) core with three metalloporphyrin units appended to it through short chiral spacers. Quite well-defined chromophore arrangements are evident by circular dichroism (CD) spectroscopy of this compound in solution, where clear exciton coupled bands of porphyrins are observed. In more polar solvents where the molecules are dispersed, a relatively weak CD signal is observed as a result of intramolecular folding, a feature confirmed by molecular modeling. The intramolecular folding was confirmed by measuring the CD of a symmetric analogue. The symmetric BTAB cores that would normally be expected to stack in a chiral arrangement in apolar solvents show no indication of CD, suggesting that there is no transfer of chirality through it (although the expected planar conformation of the 2,2'-bipyridine unit is confirmed by NMR spectroscopy). The incorporation of the porphyrins on the 3,3'-diamino-2,2'-bipyridine moiety spaced by a chiral unit leaves the latter incapable of assembling through supramolecular π-π stacking. Rather, modeling indicates that the three metalloporphyrin units interact, thanks to van der Waals interactions, favoring their close interactions over that of the BTAB units. Atomic force microscopy shows that, in contrast to other examples of molecules with the same core, disclike aggregates (rather than fibrillar one dimensional aggregates) are favored by the symmetric molecule. The closed structures are formed through nondirectional interlocking of porphyrin rings. The chiral spacer between the rigid core and the porphyrin moieties is undoubtedly important in determining the outcome in polar or less polar solvents, as modeling shows that this joint in the molecule has two favored conformations that render the molecule relatively flat or convex.
在溶解性较差的介质中，大的盘状分子之间微弱的非共价相互作用通常会导致分子彼此堆叠形成纤维。在此，我们表明，通常会导致柱状堆叠的大的芳香基团之间的特定手性间隔基团，在这种情况下，在相对极性的溶剂中会产生分子内折叠结构，但在非常非极性的溶剂中会形成有限聚集体。表现出这种行为的分子具有一个对称的苯 - 1,3,5 - 三（3,3'-二氨基 - 2,2'-联吡啶）（BTAB）核心，通过短的手性间隔基团连接有三个金属卟啉单元。通过该化合物在溶液中的圆二色性（CD）光谱可以明显看出相当明确的发色团排列，其中观察到了卟啉清晰的激子耦合带。在分子分散的极性更大的溶剂中，由于分子内折叠观察到相对较弱的CD信号，这一特征通过分子建模得到证实。通过测量对称类似物的CD证实了分子内折叠。通常预期在非极性溶剂中以手性排列堆叠的对称BTAB核心没有显示出CD迹象，这表明没有通过它传递手性（尽管通过核磁共振光谱证实了2,2'-联吡啶单元的预期平面构象）。通过手性单元间隔的3,3'-二氨基 - 2,2'-联吡啶部分上卟啉的并入使得后者无法通过超分子π - π堆叠进行组装。相反，建模表明，由于范德华相互作用，三个金属卟啉单元相互作用，相比于BTAB单元，更有利于它们紧密相互作用。原子力显微镜显示，与具有相同核心的其他分子例子相比，对称分子更倾向于形成盘状聚集体（而不是纤维状一维聚集体）。封闭结构是通过卟啉环的非定向互锁形成的。刚性核心和卟啉部分之间的手性间隔基团在决定在极性或极性较小的溶剂中的结果方面无疑很重要，因为建模表明分子中的这个连接点有两种有利的构象，使分子相对扁平或凸起。
