Molecular Engineering of Stabilized Silicon-Rosindolizine Shortwave Infrared Fluorophores.

Fluorescence-based biological imaging in the shortwave infrared (SWIR, 1000-1700 nm) is an attractive replacement for modern imaging techniques currently employed in both medical and research settings. Xanthene-based fluorophores containing heterocycle donors have recently emerged as a way to access deep SWIR emitting fluorophores. A concern for xanthene-based SWIR fluorophores though is chemical stability toward ambient nucleophiles due to the high electrophilicity of the cationic fluorophore core.

Ion mobility-tandem mass spectrometry of bulky tert-butyl thiol ligated gold nanoparticles.

Gold nanoparticles (AuNPs) synthesized in the 1-3 nm range have a specific number of gold core atoms and outer protecting ligands. They have become one of the "hot topics" in recent decades because of their interesting physical and chemical properties. The characterization of their structures is usually achieved by crystal X-ray diffraction although the structures of some AuNPs remain unknown because they have not been successfully crystallized.

Crystal structure of bulky-ligand-protected Au(S-CH).

Atomically precise thiolate-protected gold nanomolecules have attracted interest due to their distinct electronic and chemical properties. The structure of these nanomolecules is important for understanding their peculiar properties. Here, we report the X-ray crystal structure of a 24-atom gold nanomolecule protected by 16 tert-butylthiolate ligands.

Laser-based temperature control to study the roles of entropy and enthalpy in polymer-nanopore interactions.

Single-molecule approaches for probing the free energy of confinement for polymers in a nanopore environment are critical for the development of nanopore biosensors. We developed a laser-based nanopore heating approach to monitor the free energy profiles of such a single-molecule sensor. Using this approach, we measure the free energy profiles of two distinct polymers, polyethylene glycol and water-soluble peptides, as they interact with the nanopore sensor.

Size Exclusion Chromatography: An Indispensable Tool for the Isolation of Monodisperse Gold Nanomolecules.

Highly monodisperse and pure samples of atomically precise gold nanomolecules (AuNMs) are essential to understand their properties and to develop applications using them. Unfortunately, the synthetic protocols that yield a single-sized nanomolecule in a single-step reaction are unavailable. Instead, we observe a polydisperse product with a mixture of core sizes.

Crystal Structure of AuAg(S-Bu) and Effect of the Ligand on Ag Alloying in Gold Nanomolecules.

We report the X-ray crystal structure of the AuAg(S-Bu) alloy and the effect of the ligand on alloying site preferences. Gold-silver nanoalloys prepared by co-reduction of metal salts are known to have only partial Ag occupancies. Interestingly, AuAg(S-Bu) has on the surface, capping, and staples sites.

Base Side of Noble Metal Clusters: Efficient Route to Captamino-Gold, Au (-S(CH)N(CH)) , n = 25-144.

Monolayer-protected clusters (MPCs), typified by the (Au, Ag)-thiolates, share dimensions and masses with aqueous globular proteins (enzymes), yet efficient bioanalytical methods have not proved applicable to MPC analytics. Here we demonstrate that direct facile ESI(+)MS analysis of MPCs succeeds, at the few-picomol level, for aqueous basic amino-terminated thiolates. Specifically, captamino-gold clusters, Au (SR) , wherein -R = -(CH)N(CH), are prepared quantitatively via a direct one-phase (aq/EtOH) method and are sprayed under weakly acidic conditions to yield intact 6.

Isolation of a 300 kDa, Au Gold Compound, the Standard 3.6 nm Capstone to a Series of Plasmonic Nanocrystals Protected by Aliphatic-like Thiolates.

Disclosed herein is a method to obtain the ∼300 kDa gold-hexanethiolate compound, extracted from the Faradaurate series of smaller (3) and larger (1) homologues, thereby permitting the first measurement of its distinctive properties by methods including mass spectrometry, optical spectroscopy, electron microscopy, X-ray scattering, and diffraction. The results suggest a monocrystalline metallic core (free of twinning planes) of ∼3.1 nm minimum dimension, which supports a clear plasmonic optical response, along with a diffuse exterior shell.

Ligand Structure Determines Nanoparticles' Atomic Structure, Metal-Ligand Interface and Properties.

The nature of the ligands dictates the composition, molecular formulae, atomic structure and the physical properties of thiolate protected gold nanomolecules, Au(SR). In this review, we describe the ligand effect for three classes of thiols namely, aliphatic, AL or aliphatic-like, aromatic, AR, or bulky, BU thiol ligands. The ligand effect is demonstrated using three experimental setups namely: (1) The nanomolecule series obtained by direct synthesis using AL, AR, and BU ligands; (2) Molecular conversion and interconversion between Au(S-AL), Au(S-AR), and Au(S-BU) nanomolecules; and (3) Synthesis of Au, Au, and Au nanomolecules from one precursor Au(S-glutathione) upon reacting with AL, AR, and BU ligands.

Aromatic Thiolate-Protected Series of Gold Nanomolecules and a Contrary Structural Trend in Size Evolution.

Thiolate-protected gold nanoparticles (AuNPs) are a special class of nanomaterials that form atomically precise NPs with distinct numbers of Au atoms ( n) and thiolate (-SR, R = hydrocarbon tail) ligands ( m) with molecular formula [Au (SR) ]. These are generally termed Au nanomolecules (AuNMs), nanoclusters, and nanocrystals. AuNMs offer atomic precision in size, which is desired to underpin the rules governing the nanoscale regime and factors affecting the unique properties conferred by quantum confinement.

Au(SePh) nanomolecules: synthesis, optical spectroscopy and theoretical analysis.

Here, we report the synthesis of selenophenol (HSePh) protected Au36(SePh)24 nanomolecules via a ligand-exchange reaction of 4-tert-butylbenzenethiol (HSPh-tBu) protected Au36(SPh-tBu)24 with selenophenol, and its spectroscopic and theoretical analysis. Matrix assisted laser desorption ionization (MALDI) mass spectrometry, electrospray ionization (ESI) mass spectrometry and optical characterization confirm that the composition of the as synthesized product is predominantly Au36(SePh)24 nanomolecules. Size exclusion chromatography (SEC) was employed to isolate the Au36(SePh)24 and temperature dependent optical absorption studies and theoretical analysis were performed.

Au(SR): The Smallest Gold Thiolate Nanocrystal That Is Metallic and the Birth of Plasmon.

We report a detailed study on the optical properties of Au(SR) using steady-state and transient absorption measurements to probe its metallic nature, time-dependent density functional theory (TDDFT) studies to correlate the optical spectra, and density of states (DOS) to reveal the factors governing the origin of the collective surface plasmon resonance (SPR) oscillation. Au is the smallest identified gold nanocrystal to exhibit SPR. Its optical absorption exhibits SPR at 510 nm.

Crystal Structure of Faradaurate-279: Au(SPh-tBu) Plasmonic Nanocrystal Molecules.

We report the discovery of an unprecedentedly large, 2.2 nm diameter, thiolate protected gold nanocrystal characterized by single crystal X-ray crystallography (sc-XRD), Au(SPh-tBu) named Faradaurate-279 (F-279) in honor of Michael Faraday's (1857) pioneering work on nanoparticles. F-279 nanocrystal has a core-shell structure containing a truncated octahedral core with bulk face-centered cubic-like arrangement, yet a nanomolecule with a precise number of metal atoms and thiolate ligands.

Synthesis of Au(SCHCHPh), Au(SPh-tBu), and Au(S-tBu) Nanomolecules from a Common Precursor Mixture.

Phenylethanethiol protected nanomolecules such as Au, Au, and Au are widely studied by a broad range of scientists in the community, owing primarily to the availability of simple synthetic protocols. However, synthetic methods are not available for other ligands, such as aromatic thiol and bulky ligands, impeding progress. Here we report the facile synthesis of three distinct nanomolecules, Au(SCHCHPh), Au(SPh-tBu), and Au(S-tBu), exclusively, starting from a common Au(glutathione) (where n and m are number of gold atoms and glutathiolate ligands) starting material upon reaction with HSCHCHPh, HSPh-tBu, and HStBu, respectively.

Single Molecule Nanopore Spectrometry for Peptide Detection.

Sensing and characterization of water-soluble peptides is of critical importance in a wide variety of bioapplications. Single molecule nanopore spectrometry (SMNS) is based on the idea that one can use biological protein nanopores to resolve different sized molecules down to limits set by the blockade duration and noise. Previous work has shown that this enables discrimination between polyethylene glycol (PEG) molecules that differ by a single monomer unit.

Synthesis of Aromatic Thiolate-Protected Gold Nanomolecules by Core Conversion: The Case of Au(SPh-tBu).

Ultrasmall nanomolecules (<2 nm) such as Au(SCHCHPh), Au(SCHCHPh), and Au(SCHCHPh) are well studied and can be prepared using established synthetic procedures. No such synthetic protocols that result in high yield products from commercially available starting materials exist for Au(SPh-X). Here, we report a synthetic procedure for the large-scale synthesis of highly stable Au(SPh-X) with a yield of ∼42%.

Indolizine-Squaraines: NIR Fluorescent Materials with Molecularly Engineered Stokes Shifts.

The development of deep red and near infrared emissive materials with high quantum yields is an important challenge. Several classes of squaraine dyes have demonstrated high quantum yields, but require significantly red-shifted absorptions to access the NIR window. Additionally, squaraine dyes have typically shown narrow Stokes shifts, which limits their use in living biological imaging applications due to dye emission interference with the light source.

Au(SPh): Au Protected with Aromatic Thiolate Ligands.

Au(SR) is one of the most extensively investigated gold nanomolecules along with Au(SR) and Au(SR). However, so far it has only been prepared using aliphatic-like ligands, where R = -SCH, -SCH and -SCHCHPh. Au(SCHCHPh) when reacted with HSPh undergoes core-size conversion to Au(SPh), and existing literature suggests that Au(SPh) cannot be synthesized.

AuS(SAdm): An Anisotropic Gold Nanomolecule. Optical and Photoluminescence Spectroscopy and First-Principles Theoretical Analysis.

We introduce a class of gold nanomolecules exhibiting anisotropy as a major feature by reporting steady-state and time-resolved photoluminescence and anisotropy measurements and in-depth theoretical analysis of energetics and optical response of a recently synthesized AuS(SAdm) nanomolecule (SAdm = adamantanethiol). Starting from single-crystal X-ray data showing that AuS(SAdm) exhibits a symmetry-broken structure, we unambiguously demonstrate how this translates into a striking anisotropy of its properties, for example, of its (chiro)optical absorption spectrum of great promise for sensing, optoelectronic, and electrochemical applications, and argue about the abundance and general significance of this class of compounds.

Symmetry breaking in ligand-protected gold clusters probed by nonlinear optics.

The first hyperpolarizabilities of [Au25(SR)18](-1/0) and Au38(SR)24 clusters were determined by Hyper-Rayleigh Scattering. A strong dependence on the molecular symmetry was observed, and we explore two strategies to destroy the center of inversion in [Au25(SR)18](-1/0), protection by chiral ligands and alloying of the cluster with silver. This may open new avenues to applications of Au : SR clusters in second-order nonlinear optics.

A Computational and Experimental Study of Thieno[3,4-b]thiophene as a Proaromatic π-Bridge in Dye-Sensitized Solar Cells.

Four D-π-A dyes (D=donor, A=accpetor) based on a 3,4-thienothiophene π-bridge were synthesized for use in dye-sensitized solar cells (DSCs). The proaromatic building block 3,4-thienothiophene is incorporated to stabilize dye excited-state oxidation potentials. This lowering of the excited-state energy levels allows for deeper absorption into the NIR region with relatively low molecular weight dyes.

Transformation of Au144(SCH2CH2Ph)60 to Au133(SPh-tBu)52 Nanomolecules: Theoretical and Experimental Study.

Ultrastable gold nanomolecule Au144(SCH2CH2Ph)60 upon etching with excess tert-butylbenzenethiol undergoes a core-size conversion and compositional change to form an entirely new core of Au133(SPh-tBu)52. This conversion was studied using high-resolution electrospray mass spectrometry which shows that the core size conversion is initiated after 22 ligand exchanges, suggesting a relatively high stability of the Au144(SCH2CH2Ph)38(SPh-tBu)22 intermediate. The Au144 → Au133 core size conversion is surprisingly different from the Au144 → Au99 core conversion reported in the case of thiophenol, -SPh.

X-ray Crystal Structure of Au38-xAgx(SCH2CH2Ph)24 Alloy Nanomolecules.

Herein, we report the X-ray crystallographic structure of a 38-metal atom Au-Ag alloy nanomolecule. The structure of monometallic Au38(SR)24 consists of 2 central Au atoms and 21 Au atoms forming a bi-icosahedral core protected by 6 dimeric and 3 monomeric units. In Au38-xAgx(SR)24,where x ranges from 1 to 5, the silver atoms are selectively incorporated into the Au21 bi-icosahedral core.