Yousefalizadeh Goonay, Ahmadi Shideh, Mosey Nicholas J, Stamplecoskie Kevin G
Department of Chemistry, Queen's University, 90 Bader Lane, Kingston, Ontario K7L 3N6, Canada.
Nanoscale. 2021 Jan 7;13(1):242-252. doi: 10.1039/d0nr06493a. Epub 2020 Dec 17.
Noble metal clusters have unique photophysical properties, especially as a new class of materials for multiphoton biomedical imaging. The previously studied AuSR exhibits "giant" two-photon absorbance cross sections. Herein, we investigate the origins of the large two photon absorption for AuSR, as well as 10 other Au and Ag clusters using femtosecond pump/probe transient absorption spectroscopy (fsTAS). Excited state absorbance (ESA) ubiquitous to thiolated Au and Ag clusters is used herein as an optical signature of two-photon absorbances of the 11 different Au and Ag clusters, which does not require high quantum yields of emission. The large selection of clusters, studied with a single laser system, allows us to draw conclusions on the role of the particular metal, cluster size/structure, and the effects of the ligands on the ability to absorb multiple NIR photons. The use of a laser with a 1028 nm excitation also allows us to investigate the dramatic effect of excitation wavelength and explain why laser wavelength has led to large variances in the non-linear responses reported for clusters to date. We discuss the double resonance mechanism, responsible for giant two photon absorbance cross-sections, helping match properties of metal clusters with experimental conditions for maximizing signal/response in multiphoton applications.
贵金属簇具有独特的光物理性质，尤其是作为一类新型的多光子生物医学成像材料。先前研究的AuSR表现出“巨大”的双光子吸收截面。在此，我们使用飞秒泵浦/探测瞬态吸收光谱法（fsTAS）研究了AuSR以及其他10种金和银簇的大二光子吸收的起源。本文将硫醇化金和银簇普遍存在的激发态吸收（ESA）用作11种不同金和银簇双光子吸收的光学特征，这不需要高量子产率的发射。使用单一激光系统研究大量的簇，使我们能够得出关于特定金属的作用、簇的大小/结构以及配体对吸收多个近红外光子能力的影响的结论。使用1028 nm激发的激光还使我们能够研究激发波长的显著影响，并解释为什么激光波长导致了迄今为止报道的簇的非线性响应的巨大差异。我们讨论了负责巨大双光子吸收截面的双共振机制，有助于使金属簇的性质与实验条件相匹配，以在多光子应用中最大化信号/响应。
