Thiazole-Flanked Para-Azaquinodimethane-Based Organic Polymer Semiconductors: Synthesis and Optoelectronic Properties

Modifying the polymer backbone through N⋯S non-covalent interactions is an effective approach to enhance the properties of organic semiconducting polymers. Following this strategy, we designed and synthesized two new quinoidal polymers based on asymmetric and symmetric thiazole-flanked para-azaquinodimethane (p-AQM), named PAQM-TTTz and PAQM-TzTTz. To assess the impact of the thiazole unit, we also synthesized a reference polymer, PAQM-TTT, and compared its optoelectronic, thermal, and polymer backbone planarity properties with those of PAQM-TTTz and PAQM-TzTTz. Both PAQM-TTTz and PAQM-TzTTz exhibited dual-band absorption in solution, indicating pre-aggregation due to enhanced intermolecular interactions. Both polymers exhibited a low band gap. Density functional theory (DFT) studies revealed that while the thiazole unit does not alter the bond lengths of adjacent thiophenes, but it reduces torsional disorder by forming N⋯S non-covalent interactions with adjacent thiophenes in PAQM-TTTz and PAQM-TzTTz. However, due to the reduced electron richness of the conjugated backbone, a lower charge carrier mobility was observed in field-effect transistors for PAQM-TTTz and PAQM-TzTTz in comparison to PAQM-TTT. Our results highlighted the interest of non-covalent interactions in quinoidal polymers and present an alternative design strategy to control the properties of p-AQM-based quinoidal semiconducting polymers.