Synthesis of Pyrrole Functionalized Materials for Organic Electronic Applications

Pyrrole is a well-known class of blocks used for conductive polymers and semiconducting materials applied in organic electronics. Pyrroles were initially involved in developing conducting polymer-based materials and relevant applications due to their high electron-rich properties and doping ability. Lately, pyrroles got involved in the synthesis of organic semiconducting materials. However, due to their high electron richness and elevated highest occupied molecular orbitals (HOMO), pyrrole compounds were prone to oxidize in the air; Thus, it was hard to work with pyrrole chemistry initially. Recently, scientists started to demonstrate an effective way of using electron-rich pyrrole moieties in organic semiconductors by synthesizing pyrrole-fused aromatic heterocyclic ring systems. Fusing pyrrole moieties with other stable aromatic ring systems such as thiophene has assisted pyrroles with air stability by lowering HOMO and providing an opportunity to fine-tune the bandgap. Following this, several different pyrrole-fused heterocyclic aromatic blocks such as thienopyrrole, dithienopyrrole, and thienodipyrrole were introduced and incorporated in organic semiconductors to apply them in organic electronics later. Pyrrole moieties of these blocks paved the path to perform various structural modifications through N-functionalization, leading to the development of solution-processable semiconducting materials from insoluble fused blocks. Solubilizing unit modifications on pyrrole N atoms improved the solvent compatibility of fused-ring semiconducting materials, leading to a low-cost solvent processing of such organic semiconductors. Even though pyrrole-containing fused-ring blocks are advantageous in developing hole-transporting semiconductors due to their electron richness, there are still not many studies performed to identify various other potential fused-pyrrole blocks that can be used in the hole transporting semiconductors. Thus, it is necessary to systematically design various pyrrole-functionalized blocks and materials for applying them in organic electronics to fully understand their structure-property relationship with regards to the development of hole transporting solution processable materials. In this study, such pyrrole functionalized organic small molecular materials were systematically investigated to reveal their structure-property relationship and OFETs application potentials. In regards to this, Chapter 1 summarizes the evolution of organic semiconductors, pyrrole-based semiconducting materials applied in organic electronics, and other related potential donors & acceptor blocks. In Chapter 2, we have demonstrated synthesis and OFETs applications of thiophene or furan spacers flanked siloxane side-chain modified diketopyrrolopyrrole (DPP) acceptors and thienopyrrole donors containing small molecules. This is the first-time report of DPP and thienopyrrole containing small molecules applied in OFETs. In Chapter 3, understudied 1H-indole and pyrrolopyridine potential donor blocks were incorporated in thiophene spacers flanked benzothiadiazole-based donor-acceptor small molecules for applying them in OFETs to understand the potential of these pyrrole-based materials in OFETs. In Chapter 4, an extension to the study in chapter 3 was performed by systematically varying the chalcogenophehene spacer flanked to benzothiadiazole in 1H-indole-benzothiadiazole-based donor-acceptor small molecular design to further investigate the structure-property relationship of the fused-pyrrole containing small molecular systems and their OFETs application potentials.