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Ligand-dependent aggregation-enhanced photoacoustic of atomically precise metal nanocluster
Aggregate ( IF 13.9 ) Pub Date : 2023-08-03 , DOI: 10.1002/agt2.401
Changlin Zhou ₁ , Meng Wang ₁ , Qiaofeng Yao ₂ , Yu Zhou ₁ , Chuantao Hou ₁ , Jianfei Xia ₁ , Zonghua Wang ₁ , Jishi Chen _{1,

3} , Jianping Xie _{4,

5}

Affiliation

Atomically precise metal nanoclusters (MNCs), as a potential type of photoacoustic (PA) contrast agent, are limited in application due to their low PA conversion efficiency (PACE). Here, with hydrophilic Au₂₅SR₁₈ (SR = thiolate) as model NCs, we present a result that weakly polar solvent induces aggregation, which effectively enhances PA intensity and PACE. The PA intensity and PACE are highly dependent on the degree of aggregation, while the aggregation-enhanced PA intensity (AEPA) positively correlates to the protected ligands. Such an AEPA phenomenon indicates that aggregation actually accelerates the intramolecular motion of Au NCs, and enlarges the proportion of excited state energy dissipated through vibrational relaxation. This result conflicts with the restriction of intramolecular motion mechanism of aggregation-induced emission. Further experiments show that the increased energy of AEPA originates from the aggregation inhibiting the intermolecular energy transfer from excited Au NCs to their surrounding medium molecules, including solvent molecule and dissolved oxygen, rather than restricting radiative relaxations. This study develops a new strategy for enhancing the PA intensity of Au NCs, and contributes to a deeper understanding of the origin of the PA signal and the excited state energy dissipation processes for MNCs.

中文翻译：

原子级精确金属纳米团簇的配体依赖性聚集增强光声

原子精确金属纳米团簇（MNC）作为一种潜在的光声（PA）造影剂，由于其低PA转换效率（PACE）而限制了其应用。在这里，我们以亲水性 Au ₂₅ SR ₁₈ (SR = 硫醇盐) 作为模型 NC，得出弱极性溶剂诱导聚集的结果，从而有效增强 PA 强度和 PACE。PA 强度和 PACE 高度依赖于聚集程度，而聚集增强 PA 强度 (AEPA) 与受保护的配体呈正相关。这种AEPA现象表明，聚集实际上加速了Au NCs的分子内运动，并扩大了通过振动弛豫耗散的激发态能量的比例。这一结果与聚集诱导发射的分子内运动机制的限制相冲突。进一步的实验表明，AEPA能量的增加源于聚集抑制从激发的Au NCs到其周围介质分子（包括溶剂分子和溶解氧）的分子间能量转移，而不是限制辐射弛豫。这项研究开发了一种增强Au NCs PA强度的新策略，有助于更深入地了解PA信号的起源和MNCs的激发态能量耗散过程。

更新日期：2023-08-03

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