Excited-State Dynamics of Photoluminescent Gold Nanoclusters and Their Assemblies with Quantum Dot Donors

Abstract

Gold nanoclusters (AuNCs) are a recently developed class of photoluminescent nanomaterial with potential for detection and imaging applications in both chemistry and biology. The AuNC small size (Au104NC) in combination with their long-lived, near-infrared (NIR) emission suggests that they could be applied as a biological label directly and also as a potential acceptor for energy transfer-based biosensing. Previous studies have shown that functionalized AuNCs can act as energy-transfer acceptors; however, the underlying mechanism appears to be complex and does not necessarily follow a classical Förster process with a (1/R)6 distance dependence. Here, we report a femtosecond and nanosecond time-resolved spectroscopy study to examine the energy dissipation and transfer processes of photoluminescent AuNC acceptors displaying different functionalized end groups and coupled with 625 nm emitting semiconductor quantum dot (QD) donors. Examination of AuNCs alone on the femtosecond timescale show coherent vibrational oscillations within the first 15 ps after excitation in the visible and NIR region. Fourier transform of the kinetic data reveal ∼0.18 and 0.40 THz low-frequency vibrations in aqueous AuNC solutions, with the latter attributed to coherent vibrations following hot electronic relaxation. A biphasic decay of the AuNC excited state on the microsecond timescales confirm their exceptionally long-lived lifetimes and that the photophysics is largely unaffected by the functional end group on the ligand. Finally, ultrafast studies of AuNCs coupled to the 625 QD donors reveal excited-state quenching and wavelength shifts of the QD’s ground-state bleach and the appearance of the excited state of the AuNC resulting from energy transfer occurring on the ∼200 ps timescale.

Synergy Between LSPR and Energy Transfer in Ultrasmall Au Nanoclusters Stabilized on Plasmonic Ag@SiO2 Nanoantenna Supports: Implication for Photocatalysis

“…In all cases, we observed an obvious distance-dependent PL quenching with a prominent quenching beyond ∼20 nm. Similar results were observed by many groups (Table S2) when plasmonic nanoparticles were used as either donors or acceptors. ,− Generally, FRET occurs by dipole–dipole coupling between donor and acceptor, and the FRET radius is typically referred to as the distance between these two dipoles. , Since the acceptor here is plasmonic nanoparticles, unlike a semiconductor, they exhibit SPR (plasmon oscillations). Therefore, the mechanism was explained by a combination of nanosurface energy transfer (NSET) and nanovolume energy transfer (NVET) processes.…”

Systematic Conversion of Photoinduced Intramolecular Electron Transfer in Trinuclear M-Ir-M (M = Re, Ir) Complexes to Intersystem Charge Transfer by Coupling to Gold Nanoclusters

“…The LMCT state of the AuNCs, characteristically, has a lifetime of around 6–7 ns, which is corroborated in our study. Although AuNCs themselves show TAS signals due to PET, but it occurs in <1 ps time scale and hence could not be observed in the specified delay time in the present experiment, which is also redundant in the present study …”

“…Although AuNCs themselves show TAS signals due to PET, but it occurs in <1 ps time scale and hence could not be observed in the specified delay time in the present experiment, which is also redundant in the present study. 63…”

Plasmonic quenching and enhancement: metal–quantum dot nanohybrids for fluorescence biosensing

“…18 Energy transfer to fluorescent Au nanoclusters was also characterized in detail and in addition to NSET, nanovolume energy transfer (NVET) was proposed as a possible mechanism. 85,86 Considering that numerous biosensing This journal is © The Royal Society of Chemistry 2023 applications using QD-to-AuNP NSET have already been reviewed in detail (cf. review papers cited above), we limit this section to the discussion of a few representative and interesting recent examples, in which metal-QD nanohybrids were used for NSET biosensing.…”