Ultrafast Relaxation Dynamics of Au₃₈(SC₂H₄Ph)₂₄ Nanoclusters and Effects of Structural Isomerism

Abstract

Structural isomerism in nanoparticle has recently emerged as a new topic and stimulated research interest because the atomic structures of ultrasmall nanoparticles may have great impact on their fundamental properties and applications. Here we report the correlation between ultrafast relaxation dynamics and atomic structures of two isomers of thiolate-protected Au 38 (SC 2 H 4 Ph) 24. The biicosahedral Au 38 (denoted as Au 38Q) with an Au 23 inner core in its atomic structure shows rapid decay (1.5 ps) followed by nanosecond relaxation to the ground state, whereas its structural isomer (Au 38T) exhibits similar relaxation processes but the rapid decay is accelerated by ~50% (1.0 ps). The fast relaxations in both cases can be assigned to core-shell charge transfer or electronic rearrangement within the metal core. The acceleration of the fast decay in Au 38T is ascribed to its unique core structure which is made up of a mono-icosahedral Au 13 capped by an Au 12 tri-tetrahedron by sharing two atoms. Interestingly, coherent phonon emissions (25 cm-1 for Au 38Q , whereas 27 and 60 cm-1 for Au 38T) are observed in both isomers with pumping in the NIR region. Our results illustrate for the first time the importance of atomic structures in the photophysics of the same sized gold nanoclusters.

Isomerization-induced enhancement of luminescence in Au28(SR)20 nanoclusters

“…69 These results are distinctly different from the coreshell relaxation mode previously observed in Au 25 (SR) 18 and Au 38 (SR) 24 nanoclusters. [57][58][59]69 Based on the femtosecond and nanosecond transient absorption measurements, the relaxation pathway for both Au 28 (SR) 20 isomers is summarized in Scheme 1 with respective time constants. Such a relaxation pathway is completely different from the previously observed two-state relaxation for Au 25 (SR) 18 and Au 38 (SR) 24 nanoclusters.…”

“…Such a relaxation pathway is completely different from the previously observed two-state relaxation for Au 25 (SR) 18 and Au 38 (SR) 24 nanoclusters. 59,60,69 The absence of core-shell electronic relaxation in both Au 28 (SR) 20 nanoclusters suggests that the electrons are mostly localized in the metal core where the TA signals originated. Therefore, the inner metal core is the key and constitutes the structural origin for the distinct differences in the PL intensity and excited state lifetime between the two Au 28 (SR) 20 nanoclusters.…”

Gold Nanoclusters: Bridging Gold Complexes and Plasmonic Nanoparticles in Photophysical Properties

“…Nanoclusters (Au 25 (SR) 18 as the example): Unlike homoleptic gold complexes, thiolate-protected gold nanoclusters are composed of a well-defined metal core and surface staple motifs (e.g., -S-Au-S-) [11]. The relaxation dynamics of gold nanoclusters of different structures have been investigated by several groups and the relaxation model is more complicated as a result of multiple contributions of both Au and S atoms to the orbitals [27,28,49,50]. Here, Au 25 (SR) 18 was chosen as an example to illustrate the photophysics.…”

“…The Au 25 (SR) 18 structure consisted of an icosahedral Au 13 core and six Au 2 (SR) 3 dimeric staple motifs for surface protection (Figure 1) [10]. With excitation at 490 nm, one can observe broad ESA overlapped with GSB peaks at 510 nm, 550 nm, and 675 nm ( Figure 6A), which is a typical feature of gold nanoclusters [2,50,51]. During the first picosecond, one can observe a broad ESA band between 500 nm and 620 nm decaying rapidly and the time constant was~600 fs ( Figure 6B).…”

“…Compared with the dynamics of the Au 10 complex, the excited state dynamics of the Au 25 nanoclusters behaved more like that of small molecules. of multiple contributions of both Au and S atoms to the orbitals [27,28,49,50]. Here, Au25(SR)18 was chosen as an example to illustrate the photophysics.…”