Surface Chemistry-Mediated Near-Infrared Emission of Small Coinage Metal Nanoparticles

Abstract

Conspectus From size-dependent luminescence to localized surface plasmon resonances, the optical properties that emerge from common materials with nanoscale dimensions have been revolutionary. As nanomaterials get smaller, they approach molecular electronic structures, and this transition from bulk to molecular electronic properties is a subject of far-reaching impact. One class of nanomaterials that exhibit particularly interesting optoelectronic features at this size transition are coinage metal (i.e., group 11 elements copper, silver, and gold) nanoparticles with core diameters between approximately 1 to 3 nm (∼25–200 atoms). Coinage metal nanoparticles can exhibit red or near-infrared photoluminescence features that are not seen in either their molecular or larger nanoscale counterparts. This emission has been exploited both as a probe of electronic behavior at the nanoscale as well as in critical applications such as biological imaging and chemical sensing. Interestingly, it has been demonstrated that their photoluminescence figures of merit such as emission quantum yield, energy, and lifetime are largely independent of particle diameter. Instead, emission from particles at this size range depends heavily on the particle surface chemistry, which includes both its metallic composition and the capping ligand architecture. The strong influence of surface chemistry on these emergent optoelectronic phenomena has powerful implications for both the study and use of these particles, primarily due to the theoretically limitless possible surface ligand architectures and metallic compositions. In this Account, we highlight recent work that studies and uses surface chemistry-mediated photoluminescence from coinage metal nanoparticles. Specifically, we emphasize the distinct, as well as synergistic, roles of the nanoparticle capping ligand and the nanoparticle core for controlling and/or enhancing their near-infrared photoluminescence. We then discuss the implications of surface chemistry-mediated photoluminescence as it relates to downstream applications such as energy transfer, sensing, and biological imaging. We conclude by discussing current challenges that remain in the field, including opportunities to develop new particle synthetic routes, analytical tools, and physical frameworks with which to understand small nanoparticle emission. Taken together, we anticipate that these materials will be foundational both in understanding the unique transition from molecular to bulk electronic structures and in the development of nanomaterials that leverage this transition.

Bright NIR‐II Photoluminescence in Rod‐Shaped Icosahedral Gold Nanoclusters

“…This "central lock-atom" strategy for the suppression of non-radiative transitions and the enhancement of PL is different from the previous strategy for the PL enhancement of gold nanoclusters which is based on surface engineering. [9,11,38,39] It should be noted that very recently, Yamamoto et al [40] reported that the central Ag atom could enhance the phosphorescence of platinum nanoclusters.…”

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial

“…Stabilizing agents (SAs) used for the preparation of nanoparticles in solution are of tremendous importance for the control of their size and shape [1–7] as well as for their colloidal stability [8–11] . Their role on the nanomaterial's properties is also established for magnetic, [8,12] optical, [13–15] thermoelectric, [16] catalytic properties, [17–21] and biocompatibility [22–24] . However, so far, their role on the physical state of bulk hybrid organic‐inorganic materials ( i. e .…”

Atomic‐Precision Gold Clusters for NIR‐II Imaging

“…Compared with Au atom, Cu and Zn atoms possess significantly less d orbital energy level, and doping can introduce the empty band and increase the efficiency of radiative recombination, although no obvious energy level shift at HOMO is found. Therefore, the NIR‐II fluorescence could be optimized by adjusting the ligand and metal doping separately, and the two factors are intertwined as different metal doping inevitably changes the electron transfer between surface ligands and metal cores …”