Synthesis, characterization, and photophysical properties of platinum(ii) terpyridyl-based multi-component systems

Abstract

Four new Pt(II) terpyridyl acetylide complexes are reported which possess either a viologen or nicotinamide unit attached as an electron acceptor via the benzylic carbon of the tolyl-terpyridine ligand. Specifically, the donor–chromophore–acceptor (D–C–A) triads prepared are [Pt(ttpy-MV)C≡C–C₆H₄–NH–CO–C₆H₂(OMe)₃](PF₆)₃ [1], where ttpy-MV = 4′-([4-methyl-4,4′-bipyridin]-ylmethyl-phenyl)-[2,2′;6′,2″]terpyridine and C≡C–C₆H₄–NH–CO–C₆H₂(OMe)₃ = N-(4-ethynylphenyl)-3,4,5-trimethoxybenzamide and [Pt(ttpy-Nd)C≡C–C₆H₄–NH–CO–C₆H₂(OMe)₃](PF₆)2 [2], where ttpy-Nd = 4′-([3-carboxamide-pyridin]-ylmethyl-phenyl)-[2,2′;6′,2″]terpyridine. The related chromophore–acceptor (C–A) dyads, [Pt(ttpy-MV)C≡CPh](PF₆)₃ [3], where C≡CPh = phenylacetylide and [Pt(ttpy-Nd)C≡CPh](PF₆)2 [4], were also prepared. The syntheses of the above compounds are achieved by the reaction of a prepared cuprous phenylacetylide compound with the appropriate platinum terpyridyl chloride complex. This change from the CuI-catalyzed acetylide coordination, which requires basic conditions, results from the observed sensitivity of the pyridinium type acceptors to base. While the parent chromophore, [Pt(ttpy)C≡CPh]PF₆ [5], where ttpy = 4′-p-tolyl-[2,2′;6′,2″]terpyridine, is brightly emissive in fluid solution, both of the aforementioned D–C–A triads 1 and 2 are nonemissive at room temperature. Of the related C–A dyads, 4 is emissive and 3 is very weakly emissive. Transient absorption studies reveal that the nicotinamide acceptor does not function as an oxidative quencher of the excited state. In contrast, the viologen acceptor appears to function as an oxidative quencher.