Manipulation of Self-Assembled Nanostructure Dimensions in Molecular Janus Particles

Abstract

The ability to manipulate self-assembly of molecular building blocks is the key to achieving precise "bottom-up" fabrications of desired nanostructures. Herein, we report a rational design, facile synthesis, and self-assembly of a series of molecular Janus particles (MJPs) constructed by chemically linking α-Keggin-type polyoxometalate (POM) nanoclusters with functionalized polyhedral oligomeric silsesquioxane (POSS) cages. Diverse nanostructures were obtained by tuning secondary interactions among the building blocks and solvents via three factors: solvent polarity, surface functionality of POSS derivatives, and molecular topology. Self-assembled morphologies of KPOM-BPOSS (B denotes isobutyl groups) were found dependent on solvent polarity. In acetonitrile/water mixtures with a high dielectric constant, colloidal nanoparticles with nanophase-separated internal lamellar structures quickly formed, which gradually turned into one-dimensional nanobelt crystals upon aging, while stacked crystalline lamellae were dominantly observed in less polar methanol/chloroform solutions. When the crystallizable BPOSS was replaced with noncrystallizable cyclohexyl-functionalized CPOSS, the resulting KPOM-CPOSS also formed colloidal spheres; however, it failed to further evolve into crystalline nanobelt structures. In less polar solvents, KPOM-CPOSS crystallized into isolated two-dimensional nanosheets, which were composed of two inner crystalline layers of Keggin POM covered by two monolayers of amorphous CPOSS. In contrast, self-assembly of KPOM-2BPOSS was dominated by crystallization of the BPOSS cages, which was hardly sensitive to solvent polarity. The BPOSS cages formed the crystalline inner bilayer, sandwiched by two outer layers of Keggin POM clusters. These results illustrate a rational strategy to purposely fabricate self-assembled nanostructures with diverse dimensionality from MJPs with controlled molecular composition and topology.

Asymmetric Fullerene Nanosurfactant: Interface Engineering for Automatic Molecular Alignments

“…We expect the utilization of site‐selective functionalized nanoparticles to be helpful for predicting the collective interaction of surface functions of LC media and solid substrates to achieve the automatic molecular alignment. An example of this strategy is the utilization of nanoparticles with a well‐defined molecular structure and specific symmetry, e.g., fullerenes, polyhedral oligomeric silsesquioxanes, and polyoxometalates . Among them, [60]fullerene (C 60 ) is an intriguing nanoparticle, being small, stable, and readily available with its stoichiometry‐controlled Bingel–Hirsch and Retro‐Prato reactions allowing the preparation of monoadducts …”

A few rediscovered and challenging topics in polymer crystals and crystallization

“…We reason that by replacing a flexible polymeric block by these nano‐sized MNPs, the resulting self‐assembled supramolecular structures should possess feature sizes similar to the building blocks. Following this idea of molecular design, we have demonstrated several types of novel macromolecules, such as giant surfactants (MNPs tethered with polymer chains), shape amphiphiles (conjugates of MNPs through short linkers), and giant polyhedra (nano‐sized conjugates of MNPs with rigid shaped linkers), as articulated in our recent Perspective Paper . So far, widely used MNPs are derivatives of polyhedral oligomeric silsesquioxanes (POSS) and [60]fullerenes (C 60 ) …”

Scattering functions of carved-ellipsoid-shaped particles

“…With the aid of these well developed models, SAS has been broadly applied in chemical, biological and materials sciences to reveal microstructures and hierarchical structures of complex systems (Nyman, 2017;Yin, Wu, Mamontov et al, 2016;Hammouda, 2010;Zheng et al, 2017;Chu & Hsiao, 2001). However, models with more complicated topologies and fine structural details are now urgently needed because of the increasing numbers of molecules, assemblies and aggregates of various morphologies across multiple length scales that are now being investigated (Liu et al, 2016;Mü ller et al, 1995;Mü ller, Krickemeyer et al, 1999;Mü ller, Shah et al, 1999;Mü ller, Das et al, 2000;Kortz, 2000;Liu et al, 2003;Li et al, 2016). In particular, polyoxometalates (POMs), a group of nano-scaled well defined metal oxide molecular clusters from early transition metal ions, possess different shapes ranging from sphere, cylinder, core-shell, wheel and rod to lemon shaped (Mü ller et al, 2001(Mü ller et al, , 1995(Mü ller et al, , 2002Mü ller & Kö gerler, 1999;Mü ller & Gouzerh, 2012;Cronin & Mü ller, 2012;Kortz, 2000;Mü ller, Das et al, 2000).…”