Mechanism of Multiple Emission in Gold Quantum Boxes and Design Rules for Strong Near-Infrared Luminescence.
- 1Department of Chemistry, Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University, Xiangtan, Hunan411105, China.
- 2Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania15213, United States.
- 3College of Chemistry & Chemical Engineering, Hunan Normal University, Changsha, Hunan410081, China.
Abstract
Ligand-protected gold nanoclusters (Au NCs) hold great promise for near-infrared photonics and bioimaging, but their low photoluminescence quantum yields (PLQYs) and unclear emission mechanisms have limited the rational design of highly luminescent NCs. Here, we report a comprehensive theoretical investigation of the representative Au8n+4(SR)4n+8 quantum-box series (n = 3, 4, 5, 6) using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to elucidate the structure-photophysics relationship. We reveal that high structural symmetry and small aspect ratios (AR) severely limit transition dipole moments and radiative decay rates in these face-centered-cubic (FCC)-type NCs, in contrast to highly emissive hexagonal close-packed (HCP) quantum-rod analogues. On the other hand, the quantum-box NCs exhibit unusually small singlet-triplet energy gaps (ΔEST) and strong spin-orbit coupling, enabling ultrafast intersystem crossing (ISC) and reverse intersystem crossing (RISC), giving rise to simultaneous prompt fluorescence (PF), thermally activated delayed fluorescence (TADF), and phosphorescence. The small gaps arise from spatially decoupled electron-hole distributions distinct from those in organic TADF materials. Moreover, low-frequency ligand (the -R group) torsional and librational motions dominate internal conversion via large reorganization energies, while one-dimensional cluster growth modulates staple-motif packing and induces nonmonotonic, ligand-dominated nonradiative relaxation. Collectively, weak radiative transitions due to symmetry constraints and efficient nonradiative decay via unconstrained ligand vibrations account for the universally low PLQY of quantum-box Au NCs. This work clarifies the fundamental roles of symmetry, anisotropy, and ligand dynamics in luminescence, offering critical design rules for developing high-efficiency near-infrared-emissive Au NCs.
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BibTeX
@article{li2026mechanism,
title = {{Mechanism of Multiple Emission in Gold Quantum Boxes and Design Rules for Strong Near-Infrared Luminescence.}},
author = {Kang Li and Yitong Wang and Pu Wang and Rongchao Jin and Yong Pei},
journal = {ACS nano},
year = {2026},
month = oct,
doi = {10.1021/acsnano.6c13094},
url = {https://europepmc.org/article/MED/42915653},
note = {CC BY},
}
RIS
TY - JOUR
TI - Mechanism of Multiple Emission in Gold Quantum Boxes and Design Rules for Strong Near-Infrared Luminescence.
AU - Kang Li
AU - Yitong Wang
AU - Pu Wang
AU - Rongchao Jin
AU - Yong Pei
PY - 2026
DA - 2026/10/01
JO - ACS nano
DO - 10.1021/acsnano.6c13094
UR - https://europepmc.org/article/MED/42915653
AB - Ligand-protected gold nanoclusters (Au NCs) hold great promise for near-infrared photonics and bioimaging, but their low photoluminescence quantum yields (PLQYs) and unclear emission mechanisms have limited the rational design of highly luminescent NCs. Here, we report a comprehensive theoretical investigation of the representative Au8n+4(SR)4n+8 quantum-box series (n = 3, 4, 5, 6) using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to elucidate the structure-photophysics relationship. We reveal that high structural symmetry and small aspect ratios (AR) severely limit transition dipole moments and radiative decay rates in these face-centered-cubic (FCC)-type NCs, in contrast to highly emissive hexagonal close-packed (HCP) quantum-rod analogues. On the other hand, the quantum-box NCs exhibit unusually small singlet-triplet energy gaps (ΔEST) and strong spin-orbit coupling, enabling ultrafast intersystem crossing (ISC) and reverse intersystem crossing (RISC), giving rise to simultaneous prompt fluorescence (PF), thermally activated delayed fluorescence (TADF), and phosphorescence. The small gaps arise from spatially decoupled electron-hole distributions distinct from those in organic TADF materials. Moreover, low-frequency ligand (the -R group) torsional and librational motions dominate internal conversion via large reorganization energies, while one-dimensional cluster growth modulates staple-motif packing and induces nonmonotonic, ligand-dominated nonradiative relaxation. Collectively, weak radiative transitions due to symmetry constraints and efficient nonradiative decay via unconstrained ligand vibrations account for the universally low PLQY of quantum-box Au NCs. This work clarifies the fundamental roles of symmetry, anisotropy, and ligand dynamics in luminescence, offering critical design rules for developing high-efficiency near-infrared-emissive Au NCs.
SN - 1936-0851
SN - 1936-086X
ER -