Edis Kasëmi

Frustrated self-assembly of dendron and dendrimer-based supramolecular liquid crystals

A new “inverted” topological configuration is demonstrated both experimentally and theoretically for self-assembled dendron and dendrimer-based supramolecular liquid crystals in which the dendrons/dendrimers occupy the continuous domain and the ionically attached pendant chains are confined in discrete domains. All previous studies on dendrimer and dendron-based liquid crystals have reported “normal” liquid crystalline configurations in which the dendritic templates occupy discrete domains (in spherical or columnar phases) or continuous struts (in bicontinuous cubic phases), while the pendant chains occupy the continuous space-filling domain. These surprising results mandate a re-examination of the packing mechanisms for this important class of materials and open new routes to unique nanostructures of possible use in existing and emerging technologies.

Self-Assembly and Induced Circular Dichroism in Dendritic Supramolecules with Cholesteric Pendant Groups

We report on the solid-state structural features of self-assembled chiral supramolecules based on ionic complexation of chiral cholesteric pendant groups with achiral dendritic macromolecules and show that their optical activity exhibits a systematic change in the ultraviolet/visible light (UV-vis) absorption and enhancement in the circular dichroism (CD) signal, indicating the occurrence of supramolecular chirality, also referred to as induced circular dichroism (ICD). We construct a homologous series of complexes by varying systematically from 1 to 3 the generation of dendritic units contained in dendrons, dendrimers, and dendronized polymers. The structural properties of the complexes are investigated by means of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Depending on the class of dendritic molecule and the generation, lamellar, columnar hexagonal, oblique columnar, and rectangular columnar phases can be found, with a direct correlation among the degrees of freedom of the dendritic macromolecules used and the level of order achieved in the self-assembled solid-state structures. The enhancement of the optical signals of these mesoscopic structures appears to be correlated with their order in the solid state. Complexes with the longest lattice correlation lengths also show the most enhanced CD signals. These results show the unique versatility of dendritic macromolecules as supramolecular templates capable of organizing low molecular weight chiral pendant units into a variety of solid-state structures with amplified optical properties.

Photoinduced surface patterning of azobenzene-containing supramolecular dendrons, dendrimers and dendronized polymers

Ionic complexes of azobenzenes and dendritic structures are shown to exhibit efficient light-induced mass transport upon irradiation with a light interference pattern. Surface-relief gratings (SRGs) with modulation depths of up to 550 nm were successfully inscribed. We compare the SRG formation in three generations of supramolecular dendrons, dendrimers, and dendronized polymers and demonstrate that the grating formation process is destructed by the existence of self-assembled structures as well as by overly large size of the dendronic complexes.