A research group including Doctoral Student Takumi Nawata and Professor Masanori Sakamoto at the Institute of Scientific and Industrial Research, the University of Osaka, along with Program-Specific Assistant Professor Wataru Ota and Professor Tohru Sato at the Fukui Institute for Fundamental Chemistry, Kyoto University, has discovered that the luminescent properties of gold nanoclusters can be controlled by utilizing their interaction with the ligands that cap their surfaces. The findings were published in The Journal of Physical Chemistry C.
Provided by the University of Osaka
Gold nanoclusters are ultra-small particles composed of an aggregate of anywhere from a few to several hundred gold atoms. Because they exhibit minimal biological toxicity and emit near-infrared light, which easily penetrates bodily tissues, they are anticipated for application as bioprobes for internal medical imaging.
Additionally, these clusters form multiple excited states that are energetically close to one another, resulting in unique luminescent behaviors. However, guidelines for intentionally designing these excited states and controlling their luminescent properties had not yet been established.
The research group prepared gold nanoclusters with an identical core structure consisting of 36 gold atoms (Au36) and introduced three types of ligands with different electronic properties. They then analyzed the samples using a combination of luminescence measurements, theoretical calculations, and time-resolved spectroscopy to track state changes following light irradiation.
The analysis revealed that the luminescence mechanisms varied depending on the ligand type. In particular, in the Au36 clusters protected by 2-naphthalenethiol ligands, the ligands formed a novel emissive state, resulting in the observation of a three-component luminescence lifetime. This result demonstrates that multiple-emission properties can be intentionally controlled through the molecular design of the ligands.
The study clarifies that the luminescent properties of gold nanoclusters can be systematically engineered using ligands. Gold nanoclusters possessing thermally activated delayed fluorescence (TADF) and multiple-emission characteristics are expected to find applications in high-sensitivity sensing and bioimaging. This research provides a new design framework to freely express and control these luminescent properties via ligand molecular design. It is anticipated to accelerate the development of highly functional luminescent and photosensing materials, further expanding the scope of gold nanocluster applications.
Nawata commented: "Gold nanoclusters are organic-inorganic hybrid materials composed of gold atoms and organic ligands. To control their luminescent properties, we must actively leverage the characteristics of the ligands, rather than focusing solely on the atom count and structure of the gold core. In this study, we demonstrated that the orbital levels of the ligands play a crucial role in determining the luminescent properties of the gold nanoclusters. Because ligands can be designed and modified more flexibly than the gold core itself, being able to control the physical properties of gold nanoclusters through ligands will allow us to expand their potential further than ever before."
Journal Information
Publication: The Journal of Physical Chemistry C
Title: Orbitals of Molecular Ligands Control the Luminescent Excited States of Gold Clusters
DOI: 10.1021/acs.jpcc.6c02745
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