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Issue 43, 2010
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Tuning the emission properties of cyclometalated platinum(II) complexes by intramolecular electron-sink/arylethynylated ligands and its application for enhanced luminescent oxygen sensing

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Abstract

We have synthesized five novel cyclometalated Pt(II) complexes (aryl-ppy)Pt(acac) (ppy = 2-phenyl pyridine, aryl = N-butyl naphthalimide (NI) ethynylene for Pt-1, N-butyl naphthalimide (NI)–CH2 –CO– for Pt-2, 4-cyanophenyl – CH2 – CO– for Pt-3, naphthal ethynylene for Pt-4 and naphthal-diketo for Pt-5). For the first time, π-conjugation of the ppy ligands was extended via the C[triple bond, length as m-dash]C bond. Deep red/near IR emission (638 nm–700 nm) was observed for the complex containing naphthalimide ethynylene subunit (Pt-1), whereas the close analogue Pt-2 (in which the linker between the NI and the ppy subunit is a –CH2CO– group) shows a relatively blue-shifted emission (540 nm–570 nm) but much longer luminescent lifetime (τ = 25.5 μs) than Pt-1 (τ = 6.6 μs). Simultaneous fluorescence/phosphorescence emissions were observed for Pt-1 and Pt-2, but other complexes show sole phosphorescent emission. The red-shifted phosphorescence of the complexes compared to the model complex ppyPt(acac) (486 nm) was attributed to either the significant electron-sink effect of the NI fragment (Pt-1) (for which the electron withdrawing effect is stronger than the previously reported fluoren-9-one), or the extended π-conjugation of the ppy ligand (via C[triple bond, length as m-dash]C bond) (e.g.Pt-4). The substantial tuning of the emission color and the luminescent lifetimes (0.86 μs–25.5 μs) of the complexes were rationalized by theoretical calculations (DFT/TDDFT), i.e. the emissive triplet excited states were assigned as the normal 3MLCT state (give smaller τ values) or the novel ligand-localized 3IL emissive state (give larger τ values). With tuning the luminescent lifetimes, the luminescent O2 sensitivity of the complexes was improved by 117-fold (Stern–Volmer quenching constants KSV = 0.234 Torr−1 for Pt-2vs. KSV = 0.002 Torr−1 for Pt-5).

Graphical abstract: Tuning the emission properties of cyclometalated platinum(II) complexes by intramolecular electron-sink/arylethynylated ligands and its application for enhanced luminescent oxygen sensing

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Supplementary files

Article information


Submitted
07 Jun 2010
Accepted
26 Jul 2010
First published
24 Sep 2010

J. Mater. Chem., 2010,20, 9775-9786
Article type
Paper

Tuning the emission properties of cyclometalated platinum(II) complexes by intramolecular electron-sink/arylethynylated ligands and its application for enhanced luminescent oxygen sensing

W. Wu, W. Wu, S. Ji, H. Guo, P. Song, K. Han, L. Chi, J. Shao and J. Zhao, J. Mater. Chem., 2010, 20, 9775
DOI: 10.1039/C0JM01794A

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