Tuning Ag₂₉ nanocluster light emission from red to blue with one and two-photon excitation

Abstract

We demonstrate that the tuning of the light emission from red to blue in dihydrolipoic acid (DHLA) capped Ag29 nanoclusters can be trigged with one and two photon excitations. The cluster stoichiometry was determined with mass spectrometry and found to be Ag29(DHLA)12. In a detailed optical investigation, we show that these silver nanoclusters exhibit a strong red photoluminescence visible to the naked eye and characterized by a quantum yield of nearly ∼2% upon one-photon excitation. In the nonlinear optical (NLO) study of the properties of the clusters, the two-photon excited fluorescence spectra were recorded and their first hyperpolarizability obtained. The two-photon absorption cross-section at ∼800 nm for Ag29(DHLA)12 is higher than 10(4) GM and the hyperpolarizability is 106 × 10(-30) esu at the same excitation wavelength. The two-photon excited fluorescence spectrum appears strongly blue-shifted as compared to the one-photon excited spectrum, displaying a broad band between 400 and 700 nm. The density functional theory (DFT) provides insight into the structural and electronic properties of Ag29(DHLA)12 as well as into interplay between metallic subunit or core and ligands which is responsible for unique optical properties.

Bulky Counterions: Enhancing the Two‐Photon Excited Fluorescence of Gold Nanoclusters

“…Of note is that TPEF spectra of bulky cations‐Au 15 NCs, exhibiting emission bands in the blue and the red, contrast with linear photoluminescence (OPEF) spectra where emission is only observed in the red (compare Figure a and Figure b). Such a difference between emission resulting from absorption of one or two photons was already reported on DNA‐protected and thiolate‐protected silver clusters . This behavior might be accounted for the different nature of the metal‐to‐metal excitations within the gold cluster core (blue emission) and the ligand‐metal and ligand‐metal‐metal charge transfer excitations (red emission) …”

“…Such ad ifference between emissionr esulting from absorption of one or two photonsw as already reported on DNA-protected [6] and thiolate-protected silver clusters. [19] This behavior might be accounted for the different nature of the metal-to-metale xcitations within the gold cluster core (blue emission) and the ligand-metal and ligand-metal-metal charget ransfer excitations (red emission). [8,9,19] We also explored the solvent dependence of TPEF.T he TPEF intensity of both paired bulky cations,A u 15 and Au 18 NCs, significantly increases with decreasing dielectric constant of the solvent( methanol:d ielectric constant e = 32.7 versus DCM:d ielectric constant e = 8.9, see Figure 2).…”

Controlling magnetism of Au133(TBBT)52 nanoclusters at single electron level and implication for nonmetal to metal transition

“…1 Recent advances in solution-phase synthesis of atomically precise metal nanoclusters and their total structure determination by X-ray crystallography have opened up exciting opportunities for exploring the precise structure-property correlations. [1][2][3][4][5] Signicant progress has been achieved in controlling the size and structure of gold, 6-12 silver, [13][14][15][16][17][18][19][20][21] copper, [22][23][24] and alloy nanoclusters. [25][26][27][28][29][30] Such new materials hold potential in a wide range of applications, such as catalysis, chemical and biological detection, drug delivery, to name a few.…”

“…[52][53][54][55][56][57] Maran and coworkers have done a series of work on the magnetism of nanoclusters. 41 Using Au 25 (SR) 18 as an example, controlling its charge states has led to the observation of paramagnetism (e.g. neutral Au 25 ) and diamagnetism (e.g.…”

“…AE1 states of Au 25 ) probed by electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) measurements. In a simplied picture, neutral [Au 25 (SR) 18 ] 0 has an electron count of 7e (i.e. 25 À 18 ¼ 7); note that each monovalent thiolate covalently localizes one 6s 1 electron from gold.…”