Long-Lived Room Temperature Deep-Red/Near-IR Emissive Intraligand Triplet Excited State (3IL) of Naphthalimide in Cyclometalated Platinum(II) Complexes and Its Application in Upconversion

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• 作者：Wenting Wu ; Huimin Guo ; Wanhua Wu ; Shaomin Ji ; Jianzhang Zhao
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：November 21, 2011
• 年：2011
• 卷：50
• 期：22
• 页码：11446-11460
• 全文大小：973K
• 年卷期：v.50,no.22(November 21, 2011)
• ISSN：1520-510X

文摘

[CNPt(acac)] (CN = cyclometalating ligand; acac = acetylacetonato) complexes in which the naphthalimide (NI) moiety is directly cyclometalated (NI as the C donor of the C鈥揚t bond) were synthesized. With 4-pyrazolylnaphthalimide, isomers with five-membered (Pt-2) and six-membered (Pt-3) chelate rings were obtained. With 4-pyridinylnaphthalimide, only the complex with a five-membered chelate ring (Pt-4) was isolated. A model complex with 1-phenylpyrazole as the CN ligand was prepared (Pt-1). Strong absorption of visible light (蔚 = 21鈥?00 M^鈥? cm^鈥? at 443 nm for Pt-3) and room temperature (RT) phosphorescence at 630 nm (Pt-2 and Pt-3) or 674 nm (Pt-4) were observed. Long-lived phosphorescences were observed for Pt-2 (蟿_P = 12.8 渭s) and Pt-3 (蟿_P = 61.9 渭s). Pt-1 is nonphosphorescent at RT in solution because of the acac-localized T₁ excited state [based on density functional theory (DFT) calculations and spin density analysis], but a structured emission band centered at 415 nm was observed at 77 K. Time-resolved transient absorption spectra and spin density analysis indicated a NI-localized intraligand triplet excited state (³IL) for complexes Pt-2, Pt-3, and Pt-4. DFT calculations on the transient absorption spectra (T₁ 鈫?T_n transitions, n > 1) also support the ³IL assignment of the T₁ excited states of Pt-2, Pt-3, and Pt-4. The complexes were used as triplet sensitizers for triplet鈥搕riplet-annihilation (TTA) based upconversion, and the results show that Pt-3 is an efficient sensitizer with an upconversion quantum yield of up to 14.1%, despite its low phosphorescence quantum yield of 5.2%. Thus, we propose that the sensitizer molecules at the triplet excited state that are otherwise nonphosphorescent were involved in the TTA upconversion process, indicating that weakly phosphorescent or nonphosphorescent transition-metal complexes can be used as triplet sensitizers for TTA upconversion.