Department of Chemistry, University of Pittsburgh , Pittsburgh, Pennsylvania 15260, United States.
J Am Chem Soc. 2015 Nov 18;137(45):14423-9. doi: 10.1021/jacs.5b09408. Epub 2015 Nov 6.
Small gold nanoparticles (∼1.4-2.2 nm core diameters) exist at an exciting interface between molecular and metallic electronic structures. These particles have the potential to elucidate fundamental physical principles driving nanoscale phenomena and to be useful in a wide range of applications. Here, we study the optoelectronic properties of aqueous, phosphine-terminated gold nanoparticles (core diameter = 1.7 ± 0.4 nm) after ligand exchange with a variety of sulfur-containing molecules. No emission is observed from these particles prior to ligand exchange, however the introduction of sulfur-containing ligands initiates photoluminescence. Further, small changes in sulfur substituents produce significant changes in nanoparticle photoluminescence features including quantum yield, which ranges from 0.13 to 3.65% depending on substituent. Interestingly, smaller ligands produce the most intense, highest energy, narrowest, and longest-lived emissions. Radiative lifetime measurements for these gold nanoparticle conjugates range from 59 to 2590 μs, indicating that even minor changes to the ligand substituent fundamentally alter the electronic properties of the luminophore itself. These results isolate the critical role of surface chemistry in the photoluminescence of small metal nanoparticles and largely rule out other mechanisms such as discrete (Au(I)-S-R)n impurities, differences in ligand densities, and/or core diameters. Taken together, these experiments provide important mechanistic insight into the relationship between gold nanoparticle near-infrared emission and pendant ligand architectures, as well as demonstrate the pivotal role of metal nanoparticle surface chemistry in tuning and optimizing emergent optoelectronic features from these nanostructures.
小尺寸的金纳米粒子（约 1.4-2.2nm 的核心直径）存在于分子和金属电子结构之间的令人兴奋的界面上。这些粒子具有阐明驱动纳米尺度现象的基本物理原理的潜力，并在广泛的应用中具有实用性。在这里，我们研究了经过各种含硫分子配体交换后的水相膦封端金纳米粒子（核心直径=1.7±0.4nm）的光电性质。在配体交换之前，这些粒子没有观察到发射，但引入含硫配体后会引发光致发光。此外，硫取代基的微小变化会导致纳米粒子光致发光特征发生显著变化，包括量子产率，其范围从 0.13%到 3.65%，具体取决于取代基。有趣的是，较小的配体产生最强、最高能量、最窄和最长寿命的发射。这些金纳米粒子缀合物的辐射寿命测量范围从 59 到 2590μs，这表明即使配体取代基发生微小变化，也会从根本上改变发光体本身的电子性质。这些结果分离了表面化学在小金属纳米粒子光致发光中的关键作用，并在很大程度上排除了其他机制，如离散的（Au（I）-S-R）n 杂质、配体密度和/或核心直径的差异。总的来说，这些实验为金纳米粒子近红外发射与悬垂配体结构之间的关系提供了重要的机制见解，并证明了金属纳米粒子表面化学在调节和优化这些纳米结构中新兴光电特性方面的关键作用。
