Synthesis and characterization of new heterocycle-based discotic mesogens for optoelectronic applications

Abstract

Organic π-conjugated molecules are gaining significant attention because of their substantial capability of producing low-cost, eco-friendly, flexible and large-area plastic electronics. Certainly, discotic liquid crystals (DLCs) are renowned soft selfassembled one-dimensional (1-D) organic nanostructures as they possess robust cofacial π-π stacking in the longer columnar axis, which provides a significant channel for effective anisotropic charge mobility. These LC materials are recognized to possess superior potential to be utilized as active semiconducting layers in organic electronic devices in comparison to the organic single crystals or amorphous polymers in terms of several aspects. At present, a significant number of researchers are keenly working on this class of materials for their applications in future optoelectronic devices. In this context, it was planned to design, synthesize optically dynamic unconventional discotic molecules based on various heterocyclic moieties (HT1-35) and to study the structureproperty relationships. Also, it was contemplated to employ the selected LC materials in optoelectronic devices and to evaluate their performance. Based on the thorough literature survey, six series of molecules, i.e. Series-1 to 6 carrying important heterocycles appended with variety of substituted aryl motifs were designed by following different designing strategies. They were successfully synthesized using appropriate synthetic protocols and their chemical structures were confirmed by means of routine spectral techniques. Further, their liquid crystalline properties were investigated by set of standard methods. Most of the newly prepared materials were found to be rich in mesomorphism, dominated with columnar (Col) selfassembly. Furthermore, they were subjected to detailed photophysical as well as electrochemical characterizations and the obtained optoelectronic results were corroborated with theoretical simulations (DFT). Majority of them were shown to be superior light absorption and emitting materials. Finally, the columnar LC materials owning essential properties were employed as emissive layer in the fabrication of multilayer OLED devices; the attained results were promising. Conclusively, by improving the molecular design, prospective DLCs with plausible applications in molecular electronics, can be achieved.