The magneto-optical absorption properties of colloidal metal nanoclusters spanning nonmetallic to metallic regimes were examined using variable-temperature variable-field magnetic circular dichroism (VTVH-MCD) spectroscopy. Charge neutral Au₂₅(SC₈H₉)₁₈ exhibited MCD spectra dominated by Faraday C-terms, consistent with expectations for a nonmetallic paramagnetic nanocluster. This response is reconciled by the open-shell superatom configuration of Au₂₅(SC₈H₉)₁₈. Metallic and plasmon-supporting Au₄₅₉(pMBA)₁₇₀ exhibited temperature-independent VTVH-MCD spectra dominated by Faraday A-terms. Au₁₄₄(SC₈H₉)₆₀, which is intermediate to the metallic and nonmetallic limits, showed the most complex VTVH-MCD response of the three nanoclusters, consisting of 19 distinguishable peaks spanning the visible and near-infrared (3.0–1.4 eV). Variable-temperature analysis suggested that none of these transitions originated from plasmon excitation. However, evidence for both paramagnetic and mixed (i.e., nondiscrete) transitions of Au₁₄₄(SC₈H₉)₆₀ was observed. These results highlight the complexity of gold nanocluster electronic transitions that emerge as sizes approach metallic length scales. Nanoclusters in this regime may provide opportunities for tailoring the magneto-optical properties of colloidal nanostructures.

中文翻译：

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跨越非金属到金属极限的胶体金属纳米粒子中从超原子到等离子体介导的磁圆二色性的演变

使用变温变场磁圆二色性 (VTVH-MCD) 光谱检查了跨越非金属到金属体系的胶体金属纳米团簇的磁光吸收特性。电中性 Au ₂₅ (SC ₈ H ₉ ) ₁₈展示了法拉第 C 项主导的 MCD 光谱，与非金属顺磁纳米团簇的预期一致。_{此响应与 Au 25} (SC ₈ H ₉ ) ₁₈的开壳层超原子构型相协调。金属和等离子体支持 Au ₄₅₉ (pMBA) ₁₇₀展示了由法拉第 A 项主导的与温度无关的 VTVH-MCD 光谱。Au ₁₄₄ (SC ₈ H ₉ ) ₆₀介于金属和非金属极限之间，显示出三个纳米团簇中最复杂的 VTVH-MCD 响应，由 19 个可区分的峰组成，跨越可见光和近红外 (3.0–1.4 eV) ). 变温分析表明，这些转变都不是源自等离子体激元激发。_{然而，Au 144} (SC ₈ H ₉ ) ₆₀的顺磁和混合（即非离散）跃迁的证据被观测到。这些结果突出了随着尺寸接近金属长度尺度而出现的金纳米团簇电子跃迁的复杂性。这种状态下的纳米团簇可以为定制胶体纳米结构的磁光特性提供机会。