Abstract
The nonlinear optical phenomenon of two-photon absorption (TPA) has numerous applications across scientific fields. However, designing TPA materials that meet the technical requirements is challenging. The fundamental optical properties of a material depend on its density of states (DOS). Herein, we achieved efficient TPA via DOS control by tuning the orbital energy levels of gold clusters and molecular ligands. Au36(NP)24 with an atomically precise Au36 core and 24 naphtalenethiol (NP) ligands was synthesised, and the orbital hybridisation effect on the TPA cross-section, σ(2), of 6000 GM at 800 nm excitation was evaluated. Au36(NP)24 exhibited a considerably large σ(2) originated from the density of states (DOS) suitable for near-double resonance enhancement because of the hybridisation between Au36 and (NP)24 orbitals. This orbital hybridisation approach between functional molecules and a metal kernel provides a versatile design strategy for tuning the DOS of materials for various purposes including nonlinear optics.
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The data supporting the findings of this study are available within the paper and its Supplementary Information (experimental procedures, theoretical calculations and characterization data).
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