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Title: Theoretical Insights into the Origin of Photoluminescence of Au 25(SR) 18 Nanoparticles

Understanding fundamental behavior of luminescent nanomaterials upon photoexcitation is necessary to expand photocatalytic and biological imaging applications. Despite the significant amount of experimental work into the luminescence of Au 25(SR) 18 clusters, the origin of photoluminescence in these clusters still remains unclear. In this study, the geometric and electronic structural changes of the Au 25(SR) 18 (R = H, CH 3, CH 2CH 3, CH 2CH 2CH 3) nanoclusters upon photoexcitation are discussed using time-dependent density functional theory (TD-DFT) methods. Geometric relaxations in the optimized excited states of up to 0.33 Å impart remarkable effects on the energy levels of the frontier orbitals of Au 25(SR) 18 nanoclusters. This gives rise to a Stokes shift of 0.49 eV for Au 25(SH) 18 in agreement with experiments. Even larger Stokes shifts are predicted for longer ligands. Vibrational frequencies in the 75–80 cm –1 range are calculated for the nuclear motion involved in the excited-state nuclear relaxation; this value is in excellent agreement with vibrational beating observed in time-resolved spectroscopy experiments. Several excited states around 0.8, 1.15, and 1.25 eV are calculated for the Au 25(SH) 18 nanocluster. Considering the typical underestimation of DFT excitation energies, thesemore » states are likely responsible for the emission observed experimentally in the 1.15–1.55 eV range. In conclusion, all excited states arise from core-based orbitals; charge-transfer states or other “semi-ring” or ligand-based states are not implicated.« less
Authors:
 [1] ;  [1]
  1. Kansas State Univ., Manhattan, KS (United States)
Publication Date:
Grant/Contract Number:
SC0012273
Type:
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 138; Journal Issue: 35; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Kansas State Univ., Manhattan, KS (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1366552
Alternate Identifier(s):
OSTI ID: 1436125

Weerawardene, K. L. Dimuthu M., and Aikens, Christine M.. Theoretical Insights into the Origin of Photoluminescence of Au25(SR)18– Nanoparticles. United States: N. p., Web. doi:10.1021/jacs.6b05293.
Weerawardene, K. L. Dimuthu M., & Aikens, Christine M.. Theoretical Insights into the Origin of Photoluminescence of Au25(SR)18– Nanoparticles. United States. doi:10.1021/jacs.6b05293.
Weerawardene, K. L. Dimuthu M., and Aikens, Christine M.. 2016. "Theoretical Insights into the Origin of Photoluminescence of Au25(SR)18– Nanoparticles". United States. doi:10.1021/jacs.6b05293.
@article{osti_1366552,
title = {Theoretical Insights into the Origin of Photoluminescence of Au25(SR)18– Nanoparticles},
author = {Weerawardene, K. L. Dimuthu M. and Aikens, Christine M.},
abstractNote = {Understanding fundamental behavior of luminescent nanomaterials upon photoexcitation is necessary to expand photocatalytic and biological imaging applications. Despite the significant amount of experimental work into the luminescence of Au25(SR)18– clusters, the origin of photoluminescence in these clusters still remains unclear. In this study, the geometric and electronic structural changes of the Au25(SR)18– (R = H, CH3, CH2CH3, CH2CH2CH3) nanoclusters upon photoexcitation are discussed using time-dependent density functional theory (TD-DFT) methods. Geometric relaxations in the optimized excited states of up to 0.33 Å impart remarkable effects on the energy levels of the frontier orbitals of Au25(SR)18– nanoclusters. This gives rise to a Stokes shift of 0.49 eV for Au25(SH)18– in agreement with experiments. Even larger Stokes shifts are predicted for longer ligands. Vibrational frequencies in the 75–80 cm–1 range are calculated for the nuclear motion involved in the excited-state nuclear relaxation; this value is in excellent agreement with vibrational beating observed in time-resolved spectroscopy experiments. Several excited states around 0.8, 1.15, and 1.25 eV are calculated for the Au25(SH)18– nanocluster. Considering the typical underestimation of DFT excitation energies, these states are likely responsible for the emission observed experimentally in the 1.15–1.55 eV range. In conclusion, all excited states arise from core-based orbitals; charge-transfer states or other “semi-ring” or ligand-based states are not implicated.},
doi = {10.1021/jacs.6b05293},
journal = {Journal of the American Chemical Society},
number = 35,
volume = 138,
place = {United States},
year = {2016},
month = {8}
}