DESIGN, SYNTHESIS, AND DEVICE APPLICATIONS OF CHARGE TRANSPORT IN DISCOTICS

Abstract

Discotic liquid crystals (DLCs) are garnering attention as a promising class of one-dimensional organic semiconductors due to their unique structural and electronic properties. Despite the considerable promise that DLCs offer, the exploration of their application as hole transport layers (HTLs) remains limited. To date, there is only a single reported study investigating the use of DLCs in this context. This lack of extensive research highlights a substantial gap in understanding and utilizing DLCs for HTL applications. This detailed study will provide insights into the alignment, packing, and interaction of DLC molecules, which are critical factors influencing their performance as HTLs. To address this gap and facilitate broader acceptance and application of DLCs in photovoltaics technology, it is imperative to conduct a thorough investigation of their supramolecular morphology at the nanoscale. The primary objective of this thesis is to synthesize novel DLCs using diverse methodologies and thoroughly characterize them with a focus on their potential applications. We initially focused on synthesizing chiral supramolecular columnar assemblies by employing hydrogen bonding to a fluorescent core (heptazine) through two distinct strategies. One approach provided us with the insight needed to successfully synthesize fluorescent chiral DLCs. Subsequently, we synthesized unsymmetrical thiophene-fused phenazine (TFP) based-DLCs that exhibited significantly reduced polarization voltage (~ 0 V) due to the asymmetric contribution of their frontier orbitals. These DLCs exhibited outstanding hole-transporting properties without the need for additives, as well as autonomous healing properties, surpassing spiro-based systems. Next, we synthesized Tetrathiafulvalene (TTF)-based DLC which has a very low oxidation potential, making it easily oxidizable by iodine vapor. A stable diradical dication was synthesized with room-temperature DLC properties, demonstrating excellent conductivity and structural conformation changes upon oxidation. Following this, we synthesized a new diketopyrrolopyrrole (DPP) derivative. In the solid state, the DPP scaffold does not exhibit fluorescence. However, in the LC phase, the mixture displays a strong red color and demonstrates a very good average lifetime in the nanosecond range. An extraordinary change in the dielectric properties of the DPP scaffold and 4-Cyano-4' pentylbiphenyl (5CB) mixture was observed when an AC current was applied.