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Study of phosphorescent organic EL materials on single-molecule level

单分子水平磷光有机EL材料的研究

基本信息

批准号：
16550155
负责人：
VACHA Martin
金额：
$ 2.18万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

项目摘要

Single-molecule spectroscopy has been used to characterize optical properties of phosphorescent iridium complexes. For the most typical complex of Ir(ppy)_3, distributions of single molecule emission intensities show profiles asymmetrical towards higher intensities and photobleaching times depend non-linearly on the single molecule emission intensities. These characteristics can be explained as a result of modified optical properties of the complexes, either due to the inhomogeneous environment or due to partial photoreaction of individual ligands. To clarify this point, an iridium complex with one ligand modified, Irfppy(ppy)_2 has been prepared and studied in the same manner. The results indicate that Irfppy(ppy)_2 which emits light via only the aldehyde-modified ligand shows the same wide distribution of emission intensities and that in the case of Ir(ppy)_3 molecular distortion due to the surrounding matrix causes localization of the excitation on and emission from a single ligand. … More Further, picosecond laser diode and time-correlated single-photon counting have been used to study excited state relaxation of Ir(ppy)_3 on ensemble and single molecule level. While the ensemble sample emission decays with the expected 1.2 μs lifetime, decreasing sample concentration is accompanied by the appearance of a short component of 3 ns next to the long 1.2 μs component. Laser repetition frequency dependence reveals that with increasing pulse separation the relative ratio of the short component increases, pointing to the ground-state absorption as its origin. Further, the short component depends on the second power of the excitation laser intensity while for the long component the intensity dependence is linear. This fact points to two-photon absorption as the probable origin of the short component. This is confirmed by one-photon and two-photon excited single-molecule imaging, where the image excited at 488 nm and detected between 370 and 450 nm is very similar to the usual one-photon excited image. The two-photon absorption is a π-π* ligand-centered transition. After excitation, the energy is transferred via internal conversion to the ^1MLCT state from where the short-lived fluorescence is emitted. Less

单分子光谱已被用来表征磷光铱配合物的光学性质。对于最典型的Ir（ppy）_3配合物，其单分子发光强度的分布呈现出向高强度方向不对称的分布，光漂白时间与单分子发光强度呈非线性关系。这些特性可以解释为由于不均匀的环境或由于个别配体的部分光反应而导致的复合物的改性光学性质的结果。为了阐明这一点，我们用同样的方法合成并研究了一个配体修饰的铱配合物Irfppy（ppy）_2。结果表明，Irfppy（ppy）_2仅通过修饰的配体发光时，其发光强度分布也很宽，而Ir（ppy）_3由于周围基质的影响，其发光强度分布也很宽，从而导致了激发和发射的局部化。 ...更多信息利用皮秒半导体激光器和时间相关单光子计数技术，在系综和单分子水平上研究了Ir（ppy）_3的激发态弛豫。虽然总体样品发射以预期的1.2 μs寿命衰减，但随着样品浓度的降低，在长的1.2 μs分量旁边出现了3 ns的短分量。激光重复频率的依赖性表明，随着脉冲间隔的增加，短分量的相对比例增加，指向基态吸收作为其起源。此外，短分量取决于激发激光强度的二次幂，而对于长分量，强度依赖性是线性的。这一事实表明，双光子吸收可能是短分量的起源。这通过单光子和双光子激发的单分子成像来证实，其中在488 nm处激发并在370 nm和450 nm之间检测到的图像与通常的单光子激发图像非常相似。双光子吸收是π-π* 配体中心跃迁。激发后，能量通过内部转换转移到^1MLCT态，从那里发出短暂的荧光。少