Anti-Kasha emissions of single molecules in a plasmonic nanocavity
Anti-Kasha emissions of single molecules in a plasmonic nanocavity
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DOI：
10.1063/5.0102087
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发表时间：
2022-09-14
影响因子：
4.4
通讯作者：
Kim, Yousoo
中科院分区：
文献类型：
--
作者：
Imada, Hiroshi;Imai-Imada, Miyabi;Kim, Yousoo
卡莎规则通常适用于固态分子系统，其中内部转换率和振动弛豫率远远高于发光率。相比之下，在等离子体激元和物质相互作用强烈的系统中，发光速率显着增强，导致出现不遵守卡莎规则的发光。在这项工作中，我们研究了在扫描隧道显微镜 (STM) 尖端和金属基底之间形成的等离子体纳米腔中单分子、游离碱和萘酞菁镁 (H(2)Nc 和 MgNc) 的反 Kasha 发射。采用窄线可调谐激光精确揭示位于尖端下方的单个分子的激发态能级，并选择性地将其激发到特定的激发态，然后获得STM光致发光（STM-PL）光谱以揭示该状态的能量弛豫。 H(2)Nc高位态的激发引起了发射光谱的各种变化，例如展宽和新峰的出现，这意味着卡莎规则的崩溃。这些观察表明第一单重激发态 (S-1) 和第二单重激发态 (S-2) 中振动激发态的发射，以及从 S-2 到 S-1 的内部转换。此外，我们从 MgNc 的 STM-PL 测量中获得了振动激发态电子和电子振动跃迁的直接证据。本文获得的结果揭示了等离激元场下分子系统的能量动力学，并强调了使用反卡莎过程获得各种能量转换功能的可能性。由 AIP Publishing 独家许可出版。
Kasha's rule generally holds true for solid-state molecular systems, where the rates of internal conversion and vibrational relaxation are sufficiently higher than the luminescence rate. In contrast, in systems where plasmons and matter interact strongly, the luminescence rate is significantly enhanced, leading to the emergence of luminescence that does not obey Kasha's rule. In this work, we investigate the anti-Kasha emissions of single molecules, free-base and magnesium naphthalocyanine (H(2)Nc and MgNc), in a plasmonic nanocavity formed between the tip of a scanning tunneling microscope (STM) and metal substrate. A narrow-line tunable laser was employed to precisely reveal the excited-state levels of a single molecule located under the tip and to selectively excite it into a specific excited state, followed by obtaining a STM-photoluminescence (STM-PL) spectrum to reveal the energy relaxation from the state. The excitation to higher-lying states of H(2)Nc caused various changes in the emission spectrum, such as broadening and the appearance of new peaks, implying the breakdown of Kasha's rule. These observations indicate emissions from the vibrationally excited states in the first singlet excited state (S-1) and second singlet excited state (S-2), as well as internal conversion from S-2 to S-1. Moreover, we obtained direct evidence of electronic and vibronic transitions from the vibrationally excited states, from the STM-PL measurements of MgNc. The results obtained herein shed light on the energy dynamics of molecular systems under a plasmonic field and highlight the possibility of obtaining various energy-converting functions using anti-Kasha processes. Published under an exclusive license by AIP Publishing.