Syntheses of Building Blocks for Organic Magnetic Materials with Enhanced Stability

This dissertation is primarily concerned with the development of unique, open-shell organic materials. Of primary interest are π-conjugated organic diradicals with high-spin (S = 1) ground states, as well as S = ½ monoradicals with engineered properties for certain applications (e.g. the fabrication of multilayer paramagnetic films with increased morphological/chemical stability). Multistep syntheses, chemical structure elucidation, and properties of these materials are described using a host of analytical techniques (including various spectroscopies, magnetic measurements, X-ray crystallography, thermogravimetric analysis, etc.). In the first project, we describe the syntheses of several high-spin organic diradicals incorporating the 1,2,4-benzotriazinyl (Blatter) radical. High-spin organic diradicals comprise an interesting class or organic materials with potential applications in spintronics and as building blocks for novel magnetic materials. However, such applications are frequently limited by the chemical stability of the high spin assembly. By attaching an auxiliary stable radical (a nitronyl or imino nitroxide) to various positions of the 1,2,4-benzotriazinyl skeleton, we are able to create high spin diradicals with singlet-triplet energy gaps (ΔEST) on the order of RT (∼0.6 kcal mol−1) and very robust stability. For instance, high-spin diradical 1 possesses suitable stability to undergo sublimation at 140°C with no significant decomposition. [diagrams omitted] In the second/third projects, we describe the synthesis of a novel aminyl diradical precursor 4-H2, which was anticipated to generate an aminyl diradical 4 with enhanced stability and very strong ferromagnetic interactions (ΔEST ∼ an order of magnitude greater than RT). Although aminyl diradical 4 has proven difficult to generate/study, an interesting nitroxide diradical 4-O2 can be synthesized in low yield and is preliminarily evidenced to possess persistent stability. Finally, we discuss the synthesis and characterization of a monoradical, Pyr-Blatt, as well as collaborative efforts with Dr. Benedetta Casu’s group at the University of Tübingen to investigate its properties for applications in stable organic thin films. [diagrams omitted