Room-temperature phosphorescence and energy transfer in luminescent multinuclear platinum(II) complexes of branched alkynyls

A series of luminescent branched platinum(II) alkynyl complexes, [1,3,5-{RC equivalent to C(PEt3)(2)PtC equivalent to C-C6H4C equivalent to C}(3)C6H3] (R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, C6H4SAc, 1-napthyl (Np), 1-pyrenyl (Pyr), 1-anthryl-8-ethynyl (HC equivalent to CAn)), [1,3-{PyrC equivalent to C(PEt3)(2)PtC equivalent to CC6H4C equivalent to C}(2)-5-{(iPr)(3)SiC equivalent to C}C6H3], and [1,3-{PyrC equivalent to C-(PEt3)(2)PtC equivalent to CC6H4C equivalent to C}(2)-5-(HC equivalent to C)-C6H3], was successfully synthesized by using the precursors [1,3,5-{Cl(PEt3)(2)PtC equivalent to CC6H4C equivalent to C}(3)C6H3] or [1,3-{Cl(PEt3)(2)PtC equivalent to CC6H4C equivalent to C}(2)-5-{(iPr)(3)SiC equivalent to C}C6H3]. The X-ray crystal structures of [1,3,5-{MeOC6H4C equivalent to C-(PEt3)(2)PtC equivalent to CC6H4 equivalent to C}(3)C6H3] and [1,8-{Cl(PEt3)(2)PtC equivalent to C}(2)An] have been determined. These complexes were found to show long-lived emission in both solution and solid-state phases at room temperature. The emission origin of the branched complexes [1,3,5-{RC equivalent to C(PEt3)(2)PtC equivalent to CC6H4C equivalent to C}(3)C6H3] with R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, and C6H4SAc was tentatively assigned to be derived from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) (d pi(Pt)->pi*(C equivalent to CR)) character, while the emission origin of the branched complexes with polyaromatic alkynyl ligands, [1,3,5-{RC equivalent to C-(PEt3)(2)PtC equivalent to CC6H4C equivalent to C}(3)C6H3] with R=Np, Pyr, or HC equivalent to CAn, [1,3-{PyrC equivalent to C-(PEt3)(2)PtC equivalent to CC6H4C equivalent to C}(2)-5-{(iPr)(3)SiC equivalent to C}C6H3], [1,3-{PyrC equivalent to C(PEt3)(2)PtC equivalent to C-C6H4C equivalent to C}(2)-5-(HC equivalent to C)C6H3], and [1,8{Cl(PEt3)(2)PtC equivalent to C}(2)An], was tentatively assigned to be derived from the predominantly (IL)-I-3 states of the respective polyaromatic alkynyl ligands, mixed with some (MLCT)-M-3 (d pi T(Pt)->pi*(C equivalent to C-R)) character. By incorporating different alkynyl ligands into the periphery of these branched complexes, one could readily tune the nature of the lowest energy emissive state and the direction of the excitation energy transfer.