Zhou Meng, Qian Huifeng, Sfeir Matthew Y, Nobusada Katsuyuki, Jin Rongchao
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA.
Nanoscale. 2016 Apr 7;8(13):7163-71. doi: 10.1039/c6nr01008c.
Atomically precise, doped metal clusters are receiving wide research interest due to their synergistic properties dependent on the metal composition. To understand the electronic properties of doped clusters, it is highly desirable to probe the excited state behavior. Here, we report the ultrafast relaxation dynamics of doped M1@Au24(SR)18 (M = Pd, Pt; R = CH2CH2Ph) clusters using femtosecond visible and near infrared transient absorption spectroscopy. Three relaxation components are identified for both mono-doped clusters: (1) sub-picosecond relaxation within the M1Au12 core states; (2) core to shell relaxation in a few picoseconds; and (3) relaxation back to the ground state in more than one nanosecond. Despite similar relaxation pathways for the two doped nanoclusters, the coupling between the metal core and surface ligands is accelerated by over 30% in the case of the Pt dopant compared with the Pd dopant. Compared to Pd doping, the case of Pt doping leads to much more drastic changes in the steady state and transient absorption of the clusters, which indicates that the 5d orbitals of the Pt atom are more strongly mixed with Au 5d and 6s orbitals than the 4d orbitals of the Pd dopant. These results demonstrate that a single foreign atom can lead to entirely different excited state spectral features of the whole cluster compared to the parent Au25(SR)18 cluster. The detailed excited state dynamics of atomically precise Pd/Pt doped gold clusters help further understand their properties and benefit the development of energy-related applications.
原子精确的掺杂金属簇因其依赖于金属组成的协同性质而受到广泛的研究关注。为了理解掺杂簇的电子性质，探究其激发态行为是非常有必要的。在此，我们使用飞秒可见和近红外瞬态吸收光谱法报道了掺杂的M1@Au24(SR)18（M = Pd，Pt；R = CH2CH2Ph）簇的超快弛豫动力学。对于两种单掺杂簇都识别出了三个弛豫成分：（1）M1Au12核态内的亚皮秒弛豫；（2）几皮秒内的核到壳弛豫；以及（3）超过一纳秒的弛豫回到基态。尽管两种掺杂纳米簇的弛豫途径相似，但与Pd掺杂剂相比，Pt掺杂剂情况下金属核与表面配体之间的耦合加速了30%以上。与Pd掺杂相比，Pt掺杂的情况导致簇的稳态和瞬态吸收发生更为剧烈的变化，这表明Pt原子的5d轨道比Pd掺杂剂的4d轨道与Au 5d和6s轨道的混合更强。这些结果表明，与母体Au25(SR)18簇相比，单个外来原子可导致整个簇的激发态光谱特征完全不同。原子精确的Pd/Pt掺杂金簇的详细激发态动力学有助于进一步理解其性质，并有利于与能量相关应用的发展。
