Higher fluorescence in platinum(iv) orthometallated complexes of perylene imine compared with their platinum(ii) or palladium(ii) analogues?

Dalton Transactions Pub Date: 2015-08-05 DOI: 10.1039/C5DT02572A

Abstract

The reaction of 3-perylenylmethylen-4′-ethylaniline (1) with [Pt2Me4(μ-SMe2)2] (and subsequent addition of PPh3) or with [Pt2(η3-C4H7)2(μ-Cl)2] produced cyclometallated PtII complexes [Pt(C^N)Me(PPh3)] (2) and, respectively, [Pt2(C^N)2(μ-Cl)2] (3) (HC^N = 3-C20H11CH[double bond, length as m-dash]NC6H4-p-C2H5), with Pt bound to the ortho site of the perylenyl fragment. From 3 the mononuclear complexes [Pt(C^N)L2] (L2 = acac (4); S2COMe (5); S2CNEt2 (6) are easily formed. Oxidative addition of methyl iodide to the square-planar PtII complexes 2, 4, and 6 gave the corresponding cyclometallated PtIV compounds [Pt(C^N)L2MeI] 7, 8 and 9. The X-ray structures of 4, 6, and 7 show that the perylenyl fragment remains essentially flat in 4 and 6 and slightly twisted in 7. Comparison of the optical properties of these PtII complexes with those reported for similar PdII derivatives reveals that the change of metal exerts a notable influence on the UV-vis spectra. In solution at room temperature, all the Pt complexes exhibit fluorescence associated with the perylene fragment with low emission quantum yields for the PtII complexes (<1%) and remarkably higher emission values for the PtIV complexes: up to 29%, with emission lifetimes of 1–5 ns. Time-dependent density functional theory (TD-DFT) calculations were performed on the perylene imine and on representative complexes [M(C^N)(acac)] (M = Pd, Pt) and [Pt(C^N)(acac)MeI] to analyse the absorption spectra. These calculations support a perylene-dominated intraligand π–π*emissive state based on the HOMO and LUMO orbitals of the perylene chromophore, and a ligand-to-ligand charge-transfer (more intense for the PtII complex) that explains the observed influence of the metal on the absorption properties.

Graphical abstract: Higher fluorescence in platinum(iv) orthometallated complexes of perylene imine compared with their platinum(ii) or palladium(ii) analogues
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