Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
CNR-ICCOM and IPCF, Consiglio Nazionale delle Ricerche, Via G. Moruzzi, 1-56124 Pisa, Italy.
J Chem Phys. 2017 Aug 21;147(7):074301. doi: 10.1063/1.4996687.
Ligand-protected Au clusters are non-bleaching fluorescence markers in bio- and medical applications. Here we show that their fluorescence can be an intrinsic property of the Au cluster itself. We find a very intense and sharp fluorescence peak located at λ=739.2 nm (1.68 eV) for Au clusters in a Ne matrix held at 6 K. The fluorescence reflects the Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital (HOMO-LUMO) diabatic bandgap of the cluster. Au shows a very rich absorption fine structure reminiscent of well defined molecule-like quantum levels. These levels are resolved since Au has only one stable isomer (tetrahedral); therefore our sample is mono-disperse in cluster size and conformation. Density-functional theory (DFT) and time-dependent DFT calculations clarify the nature of optical absorption and predict both main absorption peaks and intrinsic fluorescence in fair agreement with experiment.
配体保护的金纳米团簇是生物和医学应用中无荧光漂白的荧光标记物。在这里，我们证明它们的荧光可以是金纳米团簇本身的固有特性。我们发现，在 6 K 的 Ne 基质中，金纳米团簇具有非常强烈和尖锐的荧光峰，位于 λ=739.2nm（1.68eV）处。该荧光反映了团簇的最高占据分子轨道-最低未占据分子轨道（HOMO-LUMO）离域能隙。金显示出非常丰富的吸收精细结构，类似于明确定义的类分子量子能级。由于金只有一种稳定的异构体（四面体），因此这些能级得以分辨；因此，我们的样品在团簇尺寸和构象上是单分散的。密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）计算阐明了光吸收的性质，并与实验相当吻合地预测了主要吸收峰和本征荧光。
