Fluorene as π-conjugation linker in N^N Pt(ii) bisacetylide complexes and their applications for triplet–triplet annihilation based upconversion
作者:Huimin Guo、Qiuting Li、Lihua Ma、Jianzhang Zhao
DOI:10.1039/c2jm32074f
日期:——
Fluorene-containing N^N Pt(II) bisacetylide complexes were prepared, in which the fluorene moieties were connected to the Pt(II) center via acetylide bonds (âCCâ). Different aryl groups were attached to the fluorene moiety, such as phenylacetylide (Pt-4), naphthalimide-4-acetylide (Pt-1) and in Pt-2, the fluorene moiety was changed to carbozale moiety. We found that with the fluorene linker between the arylacetylide and the Pt(II) center, the absorption of complexes in the visible range were intensified. All the complexes show room temperature (RT) phosphorescence. Furthermore, Pt-1 shows much longer triplet excited state lifetime (Ï = 138.1 μs) than the analogue Pt-3 (Ï = 47.4 μs). For Pt-2, with changing the fluorene moiety to carbazole moiety, the T1 state lifetime becomes much shorter (Ï = 23.0 μs). Thus the one-atom (N vs. C) difference is crucial for the photophysical properties. The triplet excited state of Pt-1 was proved to be the intraligand excited state (3IL) by nanosecond time-resolved transient absorption spectroscopy, spin density analysis and emission at 77 K. The complexes were used as triplet sensitizers for tripletâtriplet annihilation (TTA) upconversion. Upconversion quantum yield (ΦUC) up to 24.3% was observed for Pt-1. Under the same conditions the model complex Pt-4 shows no upconversion. The overall upconversion efficiency (η) of the new complexes are improved compared to the model complexes, such as Pt-2, Pt-3 and Pt-4. The improved upconversion efficiency was attributed to either the prolonged T1 excited state lifetime or the intensified absorption in the visible range. Our study on the fluorene-containing N^N Pt(II) bisacetylide complexes will be useful for designing new phosphorescent Pt(II) complexes and for their applications.
我们制备了含芴的 N^N Pt(II)双乙酰络合物,其中芴分子通过乙酰键(âCCâ)与 Pt(II)中心相连。芴基上连接了不同的芳基,如苯基乙酰化物(Pt-4)、萘二甲酰亚胺-4-乙酰化物(Pt-1),而在 Pt-2 中,芴基变成了羧基。我们发现,在芳基乙酰化物和铂(II)中心之间添加芴连接物后,配合物在可见光范围内的吸收增强。所有复合物都显示出室温磷光。此外,Pt-1 的三重激发态寿命(Ï = 138.1 δ¼s)比类似物 Pt-3 的三重激发态寿命(Ï = 47.4 δ¼s)长得多。对于 Pt-2,当芴基变为咔唑基时,T1 态寿命会变得更短(Ï = 23.0 δ¼s)。因此,一个原子(N 与 C)的差异对于光物理特性至关重要。通过纳秒时间分辨瞬态吸收光谱、自旋密度分析以及在 77 K 下的发射,证明了 Pt-1 的三重激发态是配体内激发态(3IL)。Pt-1 的上转换量子产率(δUC)高达 24.3%。在相同条件下,模型复合物 Pt-4 没有出现上转换现象。与 Pt-2、Pt-3 和 Pt-4 等模型配合物相比,新配合物的整体上转换效率(δ-)有所提高。上转换效率的提高可归因于 T1 激发态寿命的延长或可见光范围内吸收的增强。我们对含芴 N^N Pt(II)双乙酰络合物的研究将有助于设计新的磷光铂(II)络合物及其应用。