Luminescent platinum complexes: tuning and using the excited state

Abstract

The focus of recent research on square planar Pt(II) diimine dithiolate complexes has been to understand molecular factors that influence their excited state properties and to develop diad and triad systems based on them for use in light-driven reactions. Regarding the former, two series of Pt(diimine)(dithiolate) complexes have been synthesized and studied. All of the compounds display solvatochromic absorption bands and solution luminescence attributable to metal/dithiolate-to-diimine charge transfer excited states of the same orbital parentage. The excited-state energies can be tuned by approximately 1 eV through ligand variation. Excited-state redox potentials have been estimated for all of the complexes from spectroscopic and electrochemical data, and electron transfer quenching rate constants show the expected driving force dependence. Analogous Au(III) systems have been synthesized and characterized including molecular structure determinations of a cationic diimine dithiolate system and a neutral C-deprotonated-2-phenylpyridine derivative. Striking differences exist in the electronic structures of these Au(III) complexes from those of the Pt(II) systems, underscoring the key role of the metal in the excited state structure of the latter. The creation of diads and triads is being undertaken with ligand bridges capable of connecting the Pt(diimine)(dithiolate) moiety with other metal centers. Toward that end, complexes of dipyridocatecholate (dpcat) have been synthesized and characterized. These complexes may serve as models for the linking of chromophore and quencher components of a possible photosynthetic system. The dpcat complexes have been characterized by absorption and steady-state emission spectroscopies. Luminescence and redox properties of these and a related system containing a tetrapyridophenazine (tppz) bridge are described.