Time-Dependent Density Functional Theory Study on Higher Low-Lying Excited States of Au25(SR)18–
2018
Ebina, Masanori | Iwasa, Takeshi | Harabuchi, Yu | Taketsugu, Tetsuya
Gold–thiolate clusters of [Au₂₅(SR)₁₈]⁻ are known to show multiple photoluminescence below and above 2.0 eV. Although recent theoretical studies have clarified the lowest energy emission from the S₁ state originating from the Au₁₃ core, the relaxation mechanism responsible for the higher-energy emissions remains unclear. Here, we present a theoretical study on the higher low-lying excited states of [Au₂₅(SR)₁₈]⁻ (R = Me, EtPh: methyl, phenylethyl) using time-dependent density functional theory computations to gain further insights. In particular, we focused on the S₇ state because there is a large energy gap between S₆ and S₇ at the ground state geometry. Two minimum structures that are found for the S₇ state of [Au₂₅(SMe)₁₈]⁻ show different natures, namely, the Au sp-intraband and d-sp interband transitions. The intraband excited state has an energy close to the lower excited state, whereas the interband excited state has a substantial energy gap. Considering the underestimation of the excitation energy, the calculated emission energy originating from the S₇ interband excited state is reasonably assigned to the highest-energy emission.
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