Investigation of the photophysical properties & oxidation chemistry of cyclometalated bridged bis(phenylpyridine) platinum complexes

The development of new metal complexes and the investigation of their reactivity have been core tenets of coordination chemistry research since the late 1800s. In doing so, chemists have found classes of molecules that are suited for a variety of desirable applications, including anti-cancer drugs, bioimaging, sensing, and optoelectronics. Platinum complexes are especially interesting because their typical four-coordinate square planar geometry enables interesting intermolecular interactions and reactivity that can modulate the geometry, oxidation state, and photophysical properties for functional purposes. Combined with cyclometalating ligands, which are known to improve photophysical properties and thermostabilities, these complexes are attractive candidates for further exploration. Bidentate 2-phenylpyridine-based PtII complexes are of particular interest and can experience improved photophysical properties by incorporating a bridging atom to create a tetradentate complex. Although the choice of bridging atom is seemingly benign, there is no clear knowledge of its contribution to a complex’s overall photophysical properties. In addition, these complexes are known to undergo interesting redox chemistry to obtain complexes in the +3 and +4 oxidation states. In the case of PtIII complexes, dimers with metal-metal bonds are afforded. Recent efforts show these dimers can be used for reversible molecular capture or in OLEDs; however, these materials are relatively underexplored. This thesis examines the detailed photophysical properties and redox chemistry of bridged 2-phenylpyridine Pt complexes. Chapter 2 investigates how different bridging atoms affect the photophysical properties, comparing interesting phenomena such as aggregation-induced emission switching. Chapter 3 verifies the compatibility of known oxidation chemistry with N-bridged complexes and compares the photophysical properties of complexes in three different oxidation states. This chapter also describes how structural features of the PtIII dimers impact reactivity between two isomers. Chapter 4 examines how varying steric bulk on the N-bridging atom affects the photochemistry and stability of PtII and PtIII complexes. While the N-aryl dimers are sterically protected from disproportionation, N-alkyl dimers are easier to form through radical mediated photochemistry.