AMBIPOLAR RADICAL POLYMERS AND THEIR APPLICATION IN ORGANIC ELECTROMAGNETIC DEVICES

  

Radical polymers have received increased attention due to their scalable synthesis, ambient stability, optical transparency, and the ease of tuning their electronic properties. Radical polymers based on 2,2,6,6-tetramethyl-piperidin-1-yl-oxidanyl (TEMPO) have been widely synthesized and utilized in various organic-based devices. These polymers are exclusively p-type (i.e., hole-transporting) and recent interest has shifted to a search for other optoelectronic materials that can provide electron-transporting (n-type) and ambipolar properties. This would afford opportunities for advanced complementary circuitry. 

This dissertation describes the design, synthesis, optoelectronic, electrochemical and spin properties of radical polymers based on verdazyl and nitronyl-nitroxide pendant groups. Furthermore, it succinctly portrays how electronic and magnetic properties from these materials have been used to address fundamental challenges in advanced electromagnetic systems.

Chapter 1 provides a deeper understanding of the device systems that were addressed in the subsequent chapters of this work. The working principles, efficiency, and limitations of three device systems are well-described and these include electrochromic devices, spintronic devices, and organic electrochemical transistors.

Chapter 2 provides fundamental knowledge into the pendant groups that have been employed in this work. The history, synthetic routes, and modern-day chemistries of verdazyl and nitronyl nitroxide compounds are well-elucidated. This chapter also reveals approaches that can be employed in transferring spin density present in the small molecules of these pendant groups into much-larger, polymeric frameworks.

Chapter 3 provides a full description of a verdazyl polymer, polyoxo-3-(2-mercapto ethyl)-1,4-dihydro-1,2,4,5-tetrazin-6-one (PVEO) whose exciting properties have afforded it the opportunity to be employed as a counter electrode (i.e., the ion storage layer) in a high-performance electrochromic device. PVEO is viable alternative to inorganic-based materials that are presently being used in these systems.

Chapter 4 delves more into the magnetic properties of radical polymers and effectively describes how a nitronyl nitroxide polymer, poly-3-(4-(1-(3-methoxy-2-methylpropyl)-1,2,3-triazol-4-yl)phenyl)-4,4,5,5-tetramethyl-1-oxidaneyl-imidazole-3-oxide (PTNN) have been used to operate a spintronic device. The utilized spin-valve architectures, observed organic magnetoresistances, and opportunities for advanced applications are well described.

Chapter 5 provides both future perspectives and preliminary research work that have been done on how a verdazyl polymer, poly-3-(4-(1-(3-methoxy-2-methylpropyl)-1,2,3-triazol-4-yl)phenyl)-1,2,4,5-tetrazin-6-one (TA-PVEO) could serve as active layers in organic electrochemical transistors (OECTs).