Metal-Metal-to-Ligand Charge Transfer in Pt(II) Dimers Bridged by Pyridyl and Quinoline Thiols

The investigation of two distinct species of square planar dinuclear Pt(II) dimers based on anti-[Pt(C<^>N)(mu-N<^>S)](2), where C<^>N is either 2-phenylpyridine (ppy) or benzo(h)quinoline (bzq) and N<^>S is pyridine-2-thiol (pyt), 6-methylpyridine-2-thiol (Mpyt), or 2-quinolinethiol (2QT), is presented. Each molecule was thoroughly characterized with electronic structure calculations, static UV-vis and photoluminescence (PL) spectroscopy, and cyclic voltammetry, along with transient absorbance and time-gated PL experiments. These visible absorbing chromophores feature metal-metal-to-ligand charge-transfer (MMLCT) excited states that originate from intramolecular d(8)-d(8) metal-metal sigma-interactions and are manifested in the ground- and excited-state properties of these molecules. All five molecules reported (anti-[Pt(ppy)(mu-Mpyt)](2) could not be isolated), three of which are newly conceived here, possess electronic absorptions past 500 nm and high quantum yield PL emission with spectra extending into the far red (lambda(em) > 700 nm), originating from the charge-transfer state in each instance. Each chromophore displays excited-state decay kinetics adequately modeled by single exponentials as recorded using dynamic absorption and PL experiments; each technique yields similar decay kinetics. The combined data illustrate that pyridyl and quinoline-thiolates in conjunction with select cyclometalates represent classes of MMLCT chromophores that exhibit excited-state properties suitable for promoting light-energized chemical reactions and provide a molecular platform suitable for evaluating coherence phenomena in transient metal-metal bond-forming photochemistry.