Platinum(II) Charge Transfer Chromophores: Electrochemistry, Photophysics, and Vapochromic Sensing Applications

Square planar platinum(II) complexes have demonstrated promise in a range of applications due to their interesting ground and excited state properties. It is therefore vital to understand how to control the physical and chemical properties of such metal-organic chromophores in order to be able to tune their photophysical properties according to application-specific requirements. Hence, this dissertation research focuses on the photophysical, electrochemical, and spectroelectrochemical properties of a variety of organometallic platinum(II) complexes which possess accessible ligand-centered and charge transfer excited states. In addition to these interesting solution phase properties, metal-metal interactions in the solid state can be profoundly perturbed by vapor adsorption, rendering significant changes to both sample color and photoluminescence in the solid state. This process of vapochromism was systematically investigated in this dissertation. All molecules investigated herein are composed of a Pt(II) metal center, a single substituted diimine or triimine ligand, and the remaining coordination site generally bears systematically altered alkyl- and arylacetylides. The most successful vapochromic materials are terpyridyl-based cationic complexes where the ancillary ligand is chloride. The first part of this dissertation describes the electrochemical and photophysical properties of novel Pt(II) complexes with systematically varied polyimine and acetylide ligands. The photophysical properties have been investigated by a variety of instrumentation techniques, including absorption spectrophotometry, steady-state and time-resolved photoluminescence spectroscopy, and nanosecond laser flash photolysis/transient absorption spectroscopy. The electrochemical and spectroelectrochemical properties were studied by cyclic, pulse and wave voltammetry techniques, controlled potential electrolysis, and chronoamperometry. Chapter 2 describes the details of the instrumentation and methods employed for the compilation of this study. In the following chapter, two Pt(II) polyimine complexes that possess peryleneylacetylide ligand(s) are reported. Near-IR phosphorescence at room temperature in fluid solution is observed from these chromophores where the singlet metal-to-ligand charge transfer (MLCT) transitions are utilized to sensitize the perylenylacetylide-localized triplet excited states (3π-π*). These long-lived triplet states possess characteristic excited state absorption properties and have been shown to photochemically sensitize singlet oxygen, which was identified by its unique emission spectrum centered near 1270 nm in the near-IR. The final chapter focuses on the synthesis, characterization and the vapochromic sensing applications of mononuclear Pt(II) salts in addition to other Pt(II) complexes synthesized in our laboratory. A novel approach taken here involved the utilization of alkoxy-substituted terpyridine ligands known to facilitate π-stacking in the solid state. It was anticipated that ligand-based π-π interactions would help promote d8-d8 metal-metal interactions resulting in a new generation of vapochromic sensors based on synthetically facile materials. The development of chemical sensors that detect volatile organic compounds (VOCs) by unique and reversible color and luminescence changes were demonstrated by developing cross-responsive microarrays that are composed of various Pt(II) polyimine chromophores. These “artificial noses” were successful in rapidly detecting a variety of chemical analytes and in several instances the processes are completely reversible suggesting re-useable sensor arrays based on these Pt(II) materials