Bäumer Nils, Kartha Kalathil K, Palakkal Jasnamol P, Fernández Gustavo
Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany.
Soft Matter. 2020 Aug 7;16(29):6834-6840. doi: 10.1039/d0sm00537a. Epub 2020 Jul 7.
Controlling the supramolecular self-assembly of π-conjugated systems into defined morphologies is a prerequisite for the preparation of functional materials. In recent years, the development of sophisticated sample preparation protocols and modulation of various experimental conditions (solvent, concentration, temperature, etc.) have enabled precise control over aggregation pathways of different types of monomer units. A common method to achieve pathway control consists in the combination of two miscible solvents in defined proportions - a "poor" and "good" solvent. However, the role of solvents of opposed polarity in the self-assembly of a given building block still remains an open question. Herein, we unravel the effect of aggregation-inducing solvent systems of opposed polarity (aqueous vs. non-polar media) on the supramolecular assembly of a new bolaamphiphilic Pt(ii) complex. A number of experimental methods show a comparable molecular packing in both media driven by a synergy of solvophobic, aromatic and weak hydrogen-bonding interactions. However, morphological analysis of the respective aggregates in aqueous and non-polar media reveals a restricted aggregate growth in aqueous media into spherical nanoparticles and a non-restricted 2D-nanosheet formation in non-polar media. These findings are attributed to a considerably more efficient solvation and, in turn, increased steric demand of the hydrophilic chains in aqueous media than in nonpolar media, which can be explained by the entrapment of water molecules in the hydrophilic aggregate shell via hydrogen bonds. Our findings reveal that the different solvation of peripheral solubilizing groups in solvents of opposed polarity is an efficient method for morphology control in self-assembly.
将π共轭体系的超分子自组装控制为特定形态是制备功能材料的前提条件。近年来，先进的样品制备方案的发展以及各种实验条件（溶剂、浓度、温度等）的调节使得能够精确控制不同类型单体单元的聚集途径。实现途径控制的一种常见方法是按特定比例混合两种可混溶的溶剂——一种“不良”溶剂和一种“良”溶剂。然而，极性相反的溶剂在给定结构单元自组装中的作用仍然是一个悬而未决的问题。在此，我们揭示了极性相反的聚集诱导溶剂体系（水性与非极性介质）对一种新型双极性两亲性Pt(ii)配合物超分子组装的影响。多种实验方法表明，在疏溶剂、芳香和弱氢键相互作用的协同作用下，两种介质中的分子堆积具有可比性。然而，对水性和非极性介质中各自聚集体的形态分析表明，水性介质中聚集体生长受限形成球形纳米颗粒，而非极性介质中则形成不受限的二维纳米片。这些发现归因于与非极性介质相比，水性介质中溶剂化效率显著更高，进而亲水性链的空间需求增加，这可以通过水分子通过氢键被困在亲水性聚集体壳中来解释。我们的研究结果表明，极性相反的溶剂中周边增溶基团的不同溶剂化作用是自组装中形态控制的一种有效方法。
