Reversible Tuning of the Plasmoelectric Effect in Noble Metal Nanostructures Through Manipulation of Organic Ligand Energy Levels

Thakshila Liyanage; Malpuri Nagaraju; Merrell Johnson; Barry B Muhoberac; Rajesh Sardar

doi:10.1021/acs.nanolett.9b03588

Reversible Tuning of the Plasmoelectric Effect in Noble Metal Nanostructures Through Manipulation of Organic Ligand Energy Levels

Nano Lett. 2020 Jan 8;20(1):192-200. doi: 10.1021/acs.nanolett.9b03588. Epub 2019 Dec 3.

Authors

Thakshila Liyanage¹, Malpuri Nagaraju¹, Merrell Johnson², Barry B Muhoberac¹, Rajesh Sardar¹

Affiliations

¹ Department of Chemistry and Chemical Biology and §Integrated Nanosystems Development Institute , Indiana University-Purdue University Indianapolis , 402 N. Blackford Street, LD326 , Indianapolis , Indiana 46202 , United States.
² Department of Physics , Purdue University Fort Wayne , 2101 E. Coliseum Boulevard , Fort Wayne , Indiana 46805 , United States.

PMID: 31765167
DOI: 10.1021/acs.nanolett.9b03588

Abstract

Ligand-controlled tuning of localized surface plasmon resonance (LSPR) properties of noble metal nanostructures is fundamentally important for various optoelectronic applications such as photocatalysis, photovoltaics, and sensing. Here we demonstrate that the free carrier concentration of gold triangular nanoprisms (Au TNPs) can be tuned up to 12% upon functionalization of their surface with different para-substituted thiophenolate (X-Ph-S-) ligands. We achieve this unprecedentedly large optical response (plasmoelectric effect) in TNPs through the selective manipulation of electronic processes at the Au-thiolate interface. Interestingly, thiophenolates with electron withdrawing (donating) groups (X) produce λ_LSPR blue (red) shifts with broadening (narrowing) of localized surface plasmon resonance peak (λ_LSPR) line widths. Surprisingly, these experimental results are opposite to a straightforward application of the Drude model. Utilizing density functional theory calculations, we develop here a frontier molecular orbital approach of Au-thiophenolate interactions in the solid-state to delineate the observed spectral response. Importantly, all the spectroscopic properties are fully reversible by exchanging thiophenolates containing electron withdrawing groups with thiophenolates having electron donating groups, and vice versa. On the basis of the experimental data and calculations, we propose that the delocalization of electrons wave function controls the free carrier concentration of Au and thus the LSPR properties rather than simple electronic properties (inductive and/or resonance effects) of thiophenolates. This is further supported by the experimentally determined work functions, which are tunable over 1.9 eV in the X-Ph-S-passivated Au TNPs. We believe that our unexpected finding has great potential to guide in developing unique noble metal nanostructure-organic ligand hybrid nanoconjugates, which could allow us to bypass the complications associated with off-resonance LSPR activation of noble metal-doped semiconductor nanocrystals for various surface plasmon-driven applications.

Keywords: Metal nanostructures; gold triangular nanoprisms; localized surface plasmon resonance; plasmoelectric effect; plasmon electron density; spectral reversibility; work function.