Two-Photon\nand Three-Photon Circular Dichroism of\nAu<sub>38</sub> Gold Nanoclusters Enantiomers

While\ncircular dichroism (CD) and optical activity (OA) are well\nestablished as optical effects used in characterization of chiral\nmedia, harmonic generation and multiphoton circular dichroism are\nincreasingly seen as new, convenient ways of exploring chirality thanks\nto their operation in the near-infrared range of wavelengths. However,\nquantitative data about two-photon circular dichroism (2PCD) of organic\nand inorganic materials are scarce, and even less can be found about\nthree-photon circular dichroism (3PCD). Here, we show that both 2PCD\nand 3PCD can be readily detected in chiral atomically precise gold\nnanoclusters via polarimetric Z-scan technique. We provide quantitative\ndata on 2PCD and 3PCD of both enantiomers of Au<sub>38</sub>(PET)<sub>24</sub> nanoclusters, which exhibit extraordinary chiroptical properties\narising from the interplay of several levels of molecular organization.\nInterestingly, the corresponding two- and three-photon dissymmetry\nfactors of Au<sub>38</sub>(PET)<sub>24</sub> enantiomers are significantly\nenhanced in comparison to the one-photon CD by factors of 178 and\n217, respectively.