Ultrafast Electronic Relaxation and Vibrational Cooling Dynamics of Au₁₄₄(SC₂H₄Ph)₆₀ Nanocluster Probed by Transient Mid-IR Spectroscopy

Abstract

Energy relaxation dynamics of a gold nanocluster with atomically precise composition, Au144(SC2H4Ph)60, is studied by transient mid-IR spectroscopy. The experiment is designed to simultaneously probe electronic and vibrational dynamics by using excitation at 652 nm to prepare an electronic state localized on the gold core (as shown by high level DFT calculations) and by probing a stretching vibration localized on phenyl ring of the ligand molecules. We found that electronic relaxation proceeds with a time constant of 1.5 ps simultaneously heating the phonon bath of the cluster. The heat is further dissipated to solvent with a time constant of 29 ps. The electronic relaxation time increases with increasing pump power. Absence of long-lived electronic states and power dependence of relaxation time indicate metallic behavior. The metal–ligand interface modes are strongly anharmonically coupled to the probed mode which provides connection between the cluster core temperature and the vibrational shift of the ligand molecules. The obtained results are relevant for understanding energy relaxation dynamics of nanoclusters and together with the measured absolute molar absorption coefficient of the cluster allow designing experiments for controlled heating of the cluster by continuous wave irradiation.

MicroED Structure of Au146(p-MBA)57 at Subatomic Resolution Reveals a Twinned FCC Cluster

“…Thus, Au 146 (p-MBA) 57 does not constitute an artifact of crystallization. Samples without ammonium acetate formed poorly-diffracting hexagonal plate crystals similar to those previously reported (20,26,27), whereas samples co-precipitated with ammonium acetate crystallized as needles and plates in the presence of 25% polyethylene glycol 8000 and 50mM sodium potassium phosphate (Table S2). Large crystals as well as fragmented nanocrystals (measuring less than 5µm, Fig.…”

Optical Properties of Monolayer-Protected Aluminum Clusters: Time-Dependent Density Functional Theory Study

“…In Au 102 (p-MBA) 44 , transitions below 1.0 eV are localized inside the core, transitions between ligands and core take place at ≥1.2 eV, and interband transitions from Au(5d) to Au(6sp) begin to contribute at ≥1.7 eV. 49,50,55 Photodynamics studies show that excitations of the Au 102 (p-MBA) 44 cluster relax like a molecule, whereas the Au 144 (2-PET) 60 cluster already behaves like a metal. The spectrum of the Au 144 (2-PET) 60 cluster shows hints of a localized surface plasmon resonance (LSPR), a feature that dominates spectra of large metal nanoparticles and indicates bulk behavior.…”

Evolution from the plasmon to exciton state in ligand-protected atomically precise gold nanoparticles

“…For ultrasmall non-metallic nanoclusters such as Au 25 , the emergence of discrete states and HOMO-LUMO gap gives rise to single-electron excitations (that is, excitons) and thus long-lived excited states151617. The transition from metallic to excitonic state is reflected in steady-state optical spectra of nanoparticles/nanoclusters7818, excited state lifetime1920, electron and phonon dynamics21222324, and nonlinear optical properties2125. A characteristic feature of the metallic-state particles is that the initial electron temperature is highly dependent on the pump laser intensity, and the electron–phonon coupling time exhibits high sensitivity to the pump power42627.…”