Ligand Localized Triplet Excited States in Platinum(II) Bipyridyl and Terpyridyl Peryleneacetylides

Abstract

An investigation of the photophysics of two complexes, [Pt(^tBu₃tpy)(C≡C-perylene)]BF₄ (1) and Pt(^tBu₂bpy)(C≡C-perylene)₂ (2), where ^tBu₃tpy is 4,4′,4′′-tri(tert-butyl)-2,2′:6′,2′′-terpyridine, ^tBu₂bpy is 4,4′-di(tert-butyl)-2,2′-bipyridine, and C≡C-perylene is 3-ethynylperylene, reveals that they both exhibit perylene-centered ligand localized excited triplet states (³IL) upon excitation with visible light. These complexes do not display any significant photoluminescence at room temperature but readily sensitize ¹O₂ in aerated CH₂Cl₂ solutions, as evidenced by its characteristic emission near 1270 nm. The transient absorption difference spectra were compared to bi- and tridentate phosphine peryleneacetylides intended to model the ³IL peryleneacetylide excited states in addition to the related phenylacetylide-bearing polyimine analogues, with the latter model being the respective triplet charge-transfer (³CT) excited states. The transient difference spectra of the two title compounds display excited-state absorptions largely attributable to perylene localized ³IL states yet exhibit somewhat attenuated excited-state lifetimes relative to those of the phosphine model chromophores. The abbreviated lifetimes in 1 and 2 may suggest the involvement of the energetically proximate ³CT triplet state exerting an influence on excited-state decay, and the effect appears to be stronger in 1 relative to 2, consistent with the energies of their respective ³CT states.