Room temperature photoluminescence from [Pt(4′-CCR-tpy)Cl]+ complexes

Abstract

The synthesis, photophysics, electronic structure, and electrochemical characterization of 4′-tert-butylacetylene-2,2′:6′,2″-terpyridineplatinum(II) chloride (1), 4′-phenylacetylene-2,2′:6′,2″-terpyridineplatinum(II) chloride (2), and their Zn^II analogs are described. The Pt^II complexes display interesting photophysical properties, showing vibronically resolved emission spectra at room temperature in CH₂Cl₂, resembling a ligand localized emission profile. The photophysics and ¹O₂ sensitization experiments support a triplet state assignment for these emissions which are best described as an admixture of charge transfer and ligand localized components, which decay symmetrically with time as evidenced by time resolved emission spectra. Room temperature ligand-localized fluorescence emission is observed from the zinc complexes whereas phosphorescence emission from the ³π–π* manifold was obtained at 77 K in 4 : 1 EtOH/MeOH matrices doped with 10% ethyliodide. Compounds 1 and 2 display long-lived emission at room temperature, the latter possessing a longer lifetime, higher quantum yield, and longer wavelength emission. Lowering the temperature from 298 K to 77 K induces an increase in the excited state lifetime of both platinum systems together with a blue shift in their respective emission maxima, concomitant with more pronounced vibronic structure. The data are consistent with configurationally mixed triplet excited states at room temperature which persists in 77 K glasses. The corresponding Zn(II) complexes display significantly higher energy ligand-localized phosphorescence at 77 K. This latter result suggests that the nature of the metal and/or coordination environment imparts a significant electronic pertubation into the ligand-localized triplet states of these conjugated terpyridyl structures.