Hydrogen-Bonded Small Molecules and Polymers in Organic Electronics

Organic semiconductors are important components for applications in different fields of technology, as their advantages include the possibility of low-temperature processing as well as low-cost, large-area manufacturing based on solution-based processes, compared with inorganic counterparts. These organic materials are based on pi-conjugated molecules whose arrangements across different length scales in bulk materials are an important factor that determines their macroscopic optoelectronic properties. However, the control of their complex microstructure and morphology at the nanoscale remains challenging. In the present thesis, we investigated the use of amide hydrogen bonding as an additional structural motif to control the arrangement of pi-conjugated molecules in bulk across different length scales. In the first part, we prepared a series of hydrogen-bonded, amide-functionalized oligothiophenes together with their non-hydrogen-bonded ester analogues and studied in detail the resulting structure-property relationships. Our results showed that hydrogen-bonded bithiophenes and quaterthiophenes induced a tighter packing of the molecules as compared to their non-hydrogen-bonded analogues, resulting in a larger pi-overlap. Moreover, hydrogen bonding provided an additional driving force for a preferred formation of layered structures resulting in crystalline thin films with large domain sizes. Both of these factors resulted in an excellent performance of the thin films in field-effect transistors that is on par with that of single-crystals of related quaterthiophene derivatives. In the second part, we extended the scope to polymer semiconductors. To this end, we designed and synthesized a series of polyamides that make use of bithiophene and perylene bisimide cores as model repeat units to provide optoelectronic functionality. We have studied in detail the synergistic interplay of hydrogen bonding and pi-pi interactions and their role for the resulting materials' microstructure. As a result, we found that these materials exhibited microscopic structures similar to those of industrial-grade polyamides, providing comparable thermoplastic properties. In addition, these materials showed significant charge carrier mobility. This study may, therefore, pave the way towards polyamide-based semiconductors, with a synergistic interplay of interchain hydrogen bonding and pi-pi stacking rendering them suitable for applications in which both mechanical and optoelectronic properties play an important role.