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

Abstract

A series of luminescent branched platinum(II) alkynyl complexes, [1,3,5-{RC≡C(PEt3)2PtC≡C-C6H 4C≡C}3C6H3] (R = C 6H5, C6H4OMe, C6H 4Me, C6H4CF3, C5H 4N, C6H4SAc, 1-napthyl (Np), 1-pyrenyl (Pyr), 1-anthryl-8-ethynyl (HC≡CAn)), [1,3-{PYrC≡C(PEt3) 2PtC≡CC6H4C≡C}2-5-{(iPr) 3SiC≡C}C6H3], and [1,3- {PyrC≡C(PEt3)2PtC≡CC6H 4C≡C}2-5-(HC≡C)-C6H3], was successfully synthesized by using the precursors [1,3,5-{Cl(PEt 3)2PtC≡CC6H4C≡C} 3C6H3] or [1,3-{Cl(PEt3) 2PtC≡CC6H4C≡C}2-5-{(iPr) 3SiC≡C}C6H3]. The X-ray crystal structures of [1,3,5-{MeOC6H4C≡C-(PEt 3)2PtC≡CC6H4C≡C} 3C6H3] and [1,8-{Cl(PEt3) 2PtC≡C}2An] 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≡C(PEt3)2PtC≡CC6H 4C≡C}3C6H3] with R = C 6H5, C6H4OMe, C6H 4Me, C6H4CF3, C5H 4N, and C6H4SAc was tentatively assigned to be derived from triplet states of predominantly intra-ligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) (dπ(Pt) →π*(C≡CR)) character, while the emission origin of the branched complexes with polyaromatic alkynyl ligands, [1,3,5-{RC≡C- (PEt3)2PtC≡CC6H4C≡C} 3C6H3] with R = Np, Pyr, or HC≡CAn, [1,3-{PyrC≡C-(PEt3)2PtC≡CC6H 4C≡C}2-5-{(iPr)3SiC≡ C}C 6H3], [1,3-{PyrC≡C(PEt3) 2PtC≡CC6H4C≡C}2-5- (HC≡C)C6H3], and [1,8-{Cl(PEt3) 2PtC≡C}2An], was tentatively assigned to be derived from the predominantly 3IL states of the respective polyaromatic alkynyl ligands, mixed with some 3MLCT (dπ(Pt)→π *(C≡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. © 2005 Wiley-VCH Verlag GmbH & Co.