A new study reported fcc-structured gold nanoclusters have stronger photoluminescence than non-fcc structured gold nanoclusters for structural isomerism.
This work was done by WU Zhikun and his team with Institute of Solid State Physics (ISSP).
It is well known that structural isomerism is common in organic chemistry due to the diversity of carbon bonding. There are also some theoretical studies on the structural isomerism of clusters.
However, for solid/liquid metal nanoclusters (ultra-small metal nanoparticles), it was not until 2015 that WU¡¯s group discovered the phenomenon (Nature Commun., 2015, 6, 9667).
Subsequently, some new structural isomers of metal nanoclusters have been obtained without considering the difference of ligands.
However, the second genuine structural isomers had not yet been reported, and it was a question whether there were other structural isomers in the strict sense, especially the structural isomers with significantly different atom packing of kernel (such as fcc vs non-fcc, in which the core atoms in the first pair of structural isomers are all non-fcc arrangement).
The effect of atom packing of kernel on photoluminescence is also a fundamental and interesting topic.
On the basis of the previous work (Nature Commun., 2015, 6, 9667; Nanoscale, 2017, 9, 14809), WU¡¯s group investigated the above mentioned issues.
They developed a novel ion induction method to synthesize a unique gold nanocluster, which has the same composition and different kernel atom packing as the existing Au42(TBBT) 26 cluster (Chem. Sci. 2018, 9, 2437, TBBT = 4-tert-butylbenzeniolate).
The existing Au42 cluster has a fcc arrangement for the kernel atoms, while the newly synthesized cluster has a twist mirror symmetry structure which has not been previously reported (Fig. 1a), therefore they are genuine structural isomers with significantly different kernel atom packing (fcc vs non-fcc, see Fig. 1b).
There are few reports regarding photoluminescent gold nanoparticles with fcc-structure (the nanoparticles with photoluminescent ligands are not considered herein); thus, it is anticipated that the fcc structure may be not beneficial to the emission.
Unexpectedly, experiments conducted by WU¡¯s group illustrated that fcc-Au42 has stronger emission than that of non-fcc-Au42 (see Fig. 1c), indicating that the fcc structure might NOT actually inhibit the emission compared with the non-fcc structure.
In addition, they further compared the photoluminescence intensity of another three pairs of gold nanoclusters with similar compositions (sizes) but different kernel atom packings and the experimental results showed that in all cases fcc-structured gold nanoclusters have stronger photoluminescence than non-fcc structured gold nanoclusters (see Fig. 1d-f).
This work is supported by the National Natural Science Foundation of China, Key Program of 13th Five-Year Plan, CASHIPS, Director Foundation of ISSP, etc.
Figure 1. a) The kernel structure of non-fcc Au42; b) Comparison of structural isomerism between
non-fcc and fcc Au42(TBB)26; c) Comparison of photoluminescence properties between non-fcc
and fcc Au42(TBB)26; d) Comparison of structure and photoluminescence properties between
non-fcc Au38(2,4-DMBT)24 and fcc-Au34(2,4-DMBT)22; e) Comparison of structure and
photoluminescence properties between non-fcc-Au44(TBBT)26 and fcc-Au44(TBBT)28; f)
Comparison of structure and photoluminescence properties between non-fcc Au48(TBBT)28 and
fcc Au52(TBBT)32.(Image by ZHUANG Shengli)