TY - JOUR
T1 - Ligand-and solvent-dependent electronic relaxation dynamics of Au25(SR)18 - Monolayer-protected clusters
AU - Yi, Chongyue
AU - Zheng, Hongjun
AU - Herbert, Patrick J.
AU - Chen, Yuxiang
AU - Jin, Rongchao
AU - Knappenberger, Kenneth L.
N1 - Funding Information:
KLK acknowledges financial support from an award from the National Science Foundation (CHE-1507550). RJ acknowledges the financial support from the Air Force Office of Scientific Research under AFOSR (FA9550-15-1-0154).
Publisher Copyright:
© XXXX American Chemical Society.
PY - 2017
Y1 - 2017
N2 - Electronic relaxation dynamics of Au25(PET)18-1 and Au25(PET∗)18-1 monolayer-protected clusters (MPCs) were examined using femtosecond time-resolved transient absorption spectroscopy (fsTA). The use of two different excitation wavelengths (400 and 800 nm) allowed for quantification of state-resolved and ligand-dependent carrier dynamics for gold MPCs. Specifically, one-photon 400 nm (3.1 eV) and two-photon 800 nm (1.55 eV) interband excitations promoted electrons from the MPC ligand band into gold superatom d states. Following rapid internal conversion, carriers generated by interband excitation exhibited picosecond relaxation dynamics that depended upon both ligand structure and the dielectric of the dispersing medium. These solvent-and ligand-dependent effects were attributed to charge-Transfer processes mediated by the manifold of ligand-based states. In contrast, one-photon intraband (gold sp-sp) excitation by 800 nm light resulted in solvent-and ligand-independent relaxation dynamics. The observed solvent independences of these data were attributed to internal relaxation via superatom p and d states localized to the MPC core. Effectively, these core-based transitions were screened from dielectric influences of the dispersing medium by the MPC gold- thiolate protecting units. Additionally, a low frequency (2.4 THz) modulation of TA signal amplitude was detected following intraband excitation. The 2.4 THz mode was consistent with Au-Au expansion in the MPC core. Based on these data, we conclude that intraband relaxation among the MPC Superatom states is mediated by low-frequency vibrations of the gold core. Structure-specific and state-resolved descriptions of MPC electron dynamics are necessary for integration of metal clusters as functional components in photonic materials.
AB - Electronic relaxation dynamics of Au25(PET)18-1 and Au25(PET∗)18-1 monolayer-protected clusters (MPCs) were examined using femtosecond time-resolved transient absorption spectroscopy (fsTA). The use of two different excitation wavelengths (400 and 800 nm) allowed for quantification of state-resolved and ligand-dependent carrier dynamics for gold MPCs. Specifically, one-photon 400 nm (3.1 eV) and two-photon 800 nm (1.55 eV) interband excitations promoted electrons from the MPC ligand band into gold superatom d states. Following rapid internal conversion, carriers generated by interband excitation exhibited picosecond relaxation dynamics that depended upon both ligand structure and the dielectric of the dispersing medium. These solvent-and ligand-dependent effects were attributed to charge-Transfer processes mediated by the manifold of ligand-based states. In contrast, one-photon intraband (gold sp-sp) excitation by 800 nm light resulted in solvent-and ligand-independent relaxation dynamics. The observed solvent independences of these data were attributed to internal relaxation via superatom p and d states localized to the MPC core. Effectively, these core-based transitions were screened from dielectric influences of the dispersing medium by the MPC gold- thiolate protecting units. Additionally, a low frequency (2.4 THz) modulation of TA signal amplitude was detected following intraband excitation. The 2.4 THz mode was consistent with Au-Au expansion in the MPC core. Based on these data, we conclude that intraband relaxation among the MPC Superatom states is mediated by low-frequency vibrations of the gold core. Structure-specific and state-resolved descriptions of MPC electron dynamics are necessary for integration of metal clusters as functional components in photonic materials.
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U2 - 10.1021/acs.jpcc.7b09347
DO - 10.1021/acs.jpcc.7b09347
M3 - Article
AN - SCOPUS:85032731416
SN - 1932-7447
VL - 121
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 39
ER -