title: Effect of Atomic-Scale Differences on the Self-Assembly of Thiophene-based Polycatenars in Liquid Crystalline and Organogel States.
abstract: Two series of polycatenars are reported that contain a central thiophene moiety connected to two substituted oxadiazole or thiadiazole units. The number, position, and length of the peripheral chains connected to these molecules were varied. The oxadiazole-based polycatenars exhibited columnar phases with rectangular and hexagonal or oblique symmetry, whereas the thiadiazole-based polycatenars exhibited columnar phases with rectangular and/or hexagonal symmetry. All of the compounds exhibited bright emission in the solution and thin-film states. Two oxadiazole-based molecules and one thiadiazole-based molecule exhibited supergelation ability in hydrocarbon solvents, which is mainly supported by attractive π-π interactions. These gels showed aggregation-induced enhanced emission, which is of high technological importance for applications in solid-state emissive displays. X-ray diffraction studies of the xerogel fibers of oxadiazole-based polycatenars revealed a columnar rectangular organization, whereas a hexagonal columnar arrangement was observed for thiadiazole-based polycatenars. Rheological measurements carried out on the samples quantitatively confirmed the formation of gels and showed that these gels are mechanically robust. The impact of an atomic-scale difference (oxygen to sulfur, <2 % of the molecular weight) on the self-assembly and the macroscopic properties of those self-assembled structures are clearly visualized.
authors: Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.
authors: Balaram
authors: B
authors: Pradhan
authors: Centre for Nano and Soft Matter Sciences, Bangalore, India.
authors: V M
authors: VM
authors: Vaisakh
authors: Centre for Nano and Soft Matter Sciences, Bangalore, India.
authors: Geetha G
authors: GG
authors: Nair
authors: Centre for Nano and Soft Matter Sciences, Bangalore, India.
authors: D S Shankar
authors: DS
authors: Rao
authors: Centre for Nano and Soft Matter Sciences, Bangalore, India.
authors: S Krishna
authors: SK
authors: Prasad
authors: Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India.
authors: Achalkumar Ammathnadu
authors: AA
authors: Sudhakar
keywords: columnar phases; gels; liquid crystals; polycatenars; self-assembly