Chi-Chun Tsai

Hierarchical structure and polymorphism of a sphere-cubic shape amphiphile based on a polyhedral oligomeric silsesquioxane–[60]fullerene conjugate

A shape amphiphile composed of covalently linked spherical and cubic nanoparticles with distinct symmetry ([60]fullerene (C60) and polyhedral oligomeric silsesquioxane (POSS)) was synthesized and its solid state structures were characterized. The two types of nanoparticles are known to be generally immiscible, but they were connected with a short covalent linkage forming an organic–inorganic dyad (POSS–C60) which exhibited interesting crystallization characteristics. Crystals of the dyad exhibited polymorphism with two different crystal structures: an orthorhombic and a hexagonal unit cell with symmetry groups of P21212 and P6, respectively, both of which formed an alternating bi-layered structure of POSS and C60. The different symmetry groups in the polymorphs were attributed to the different packing orientations of the POSS within each layer. In the orthorhombic unit cell, one set of the edges of the POSS moieties is parallel to the c-axis; while in the hexagonal unit cells the body-diagonal is parallel to the c-axis of the crystal. Based on the crystal packing structure and density differential, it has been determined that the hexagonal unit cell structure is the more thermodynamically stable phase. This type of bi-layered structure with an alternating conductive fullerene and insulating POSS layer structure is of great interest for various potential applications such as nano-capacitors.

Phase behaviour and Janus hierarchical supramolecular structures based on asymmetric tapered bisamide

A precisely defined molecular Janus compound based on asymmetric tapered 1,4-bis[3,4,5-tris(alkan-1-yloxy)benzamido] benzene bisamide (abbreviated as C22PhBAEO3) was designed and synthesized, and its phase behavior was fully investigated. The C22PhBAEO3 compound possesses a rigid core with three aromatic rings connected with amide bonds which possess the ability to form hydrogen (H) bonds. Three hydrophobic alkyl flexible tails and three hydrophilic flexible methyl terminated triethylene glycol tails are located at the other end. Major phase transitions and their origins in C22PhBAEO3 were studied via DSC and 1D WAXD techniques. Its hierarchical supramolecular crystal structure was further identified through combined techniques of 2D WAXD and SAXS as well as SAED. Results based on computer simulations confirmed the structure determination. It was found that the C22PhBAEO3 possesses three phases through various thermal treatments including a micro-phase separated columnar liquid crystal (col.) phase, a metastable crystal I phase and a stable crystal II phase. Among them, the crystal II phase showed that the columnar structure possesses 3D inter-column order and highly crystalline alkyl tails with a long-range overall orientational order. Four C22PhBAEO3 molecules self-assembled into a phase-separated disc with an ellipsoidal shape having a C2 symmetry along the disc normal. These discs then stacked on top of each other to generate a 1D asymmetric column through H-bonding, and further packed into a 3D long-range ordered monoclinic lattice. The unit cell parameters of this lattice were determined to be a = 5.08 nm, b = 2.41 nm, c = 0.98 nm, α = 90°, β = 90°, and γ = 70.5°. The alkyl chain tails crystallize within the hydrophobic layers and possess a relatively fixed orientation with respect to the column packing due to the selective interactions based on the hydrophobic/hydrophilic microphase separation. Both phase behaviour and unit cell structure showed significant difference compared with the symmetrically tapered counterparts. The results provided a new approach of fine-tuning not only in the Janus supramolecular structures but also in the formation pathway of the self-assembling process in order to meet the specific requirements for optical and biological applications.

Evidence of formation of site-selective inclusion complexation between β-cyclodextrin and poly(ethylene oxide)-block-poly(propylene oxide)- block-poly(ethylene oxide) copolymers

A series of inclusion complexes of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO) with beta-cyclodextrin (beta-CD) was prepared. Their formation, structure, and dynamics were investigated by solution two-dimensional rotating-frame Overhauser effect spectroscopy (2D ROESY) and one-dimensional (1D) and 2D solid-state (13)C NMR. The inclusion complexes between the PEO-b-PPO-b-PEO copolymers and the beta-CDs were formed in aqueous solution and detected by 2D ROESY. The high efficiency of cross polarization and spin diffusion experiments in (13)C solid-state NMR showed that the mobility of the PPO blocks dramatically decreases after beta-CD complexation, indicating that they are selectively incorporated onto the PPO blocks. The hydrophobic cavities of beta-CD restrict the PPO block mobility, which is evidence of the formation of inclusion complexes in the solid state. The 2D wide-line separation NMR experiments suggested that beta-CDs only thread onto the PPO blocks while forming the inclusion complexes. The stoichiometry of inclusion complexes was studied using (1)H NMR, and a 3:1 (PO unit to beta-CD) was found for all inclusion complexes, which indicated that the number of threaded beta-CDs was only dependent on the molecular weight of the PPO blocks. 1D wide angle x-ray diffraction studies demonstrated that the beta-CD in the inclusion complex formed a channel-like structure that is different from the pure beta-CD crystal structure.