Self-Assembling C_3h Star-Shaped Supramolecular Polymers

Kenneth Ko, Ajeet Kumar, and Ronald K. Castellano

Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, FL 32611-7200, USA

Interest in C_3h-symmetric ‘star-shaped’ heteroaromatic molecules has emerged from the discovery of optoelectronic and self-assembly properties unique to this class of compounds. A well-studied portion of this group is the family of benzotrithiophene (BTT)-based materials, recognized for their applications such as liquid crystals with high charge carrier mobilities, mesoporous polymers, as photoactive layers in organic photovoltaic devices, hole-transporting materials for perovskite solar cells with power conversion efficiencies up to 18.2%, and metal-organic-frameworks with molecular adsorption and sensing properties. The oxygen-based analogues of this core have been the focus of this research. Compared to oligothiophenes, furan-based systems have shown potential to be well-suited for certain applications due to more rigid planar structures, superior solubility and processability, and tighter packing as a solid despite facing challenges inherent to the group 16 analogue such as the threat of oxidation to air and a higher energy highest occupied molecular orbital (HOMO). To probe the utility of the furan-based comparator to BTTs, the benzotrifuran (BTF) core was previously synthesized and characterized by our group. To investigate the effects of supramolecular assembly on the BTF core, carboxamides were outfitted. Retaining the C_3h symmetry, a new class of BTF amides (BTFAs) were synthesized, expected to be susceptible to self-assembly analogous to the ubiquitous 1,3,5-benzotricarboxamides. Variable concentration NMR, diffusion-ordered spectroscopy (DOSY), and variable temperature UV-VIS have been used to characterize this assembly. Calling back to the BTT-based materials, a comparator C_3h symmetric tris-carboxamide has been synthesized to understand changes in nature based on self-assembly of known optoelectronic compounds.