Long-Range Plasmophore Rulers

Using on-wire lithography, we studied the emission properties of nanostructures made of a polythiophene disk separated by fixed nanoscopic distances from a plasmonic gold nanorod. The intense plasmonic field generated by the nanorod modifies the shape of the polythiophene emission spectrum, and the strong distance dependence of this modulation forms the basis for a new type of “plasmophore ruler”. Simulations using the discrete dipole approximation (DDA) quantitatively support our experimental results. Importantly, this plasmophore ruler is independent of signal intensity and is effective up to 100 nm, which is more than two times larger than any reported value for rulers based on photoluminescence processes

A Postsynthetic Modification of II–VI Semiconductor Nanoparticles to Create Tb³⁺ and Eu³⁺ Luminophores

We describe a novel method for creating luminescent lanthanide-containing nanoparticles in which the lanthanide cations are sensitized by the semiconductor nanoparticle’s electronic excitation. In contrast to previous strategies, this new approach creates such materials by addition of external salt to a solution of fully formed nanoparticles. We demonstrate this postsynthetic modification for the lanthanide luminescence sensitization of two visible emitting lanthanides (Ln), Tb³⁺ and Eu³⁺ ions, through ZnS nanoparticles in which the cations were added postsynthetically as external Ln­(NO₃)₃·<i>x</i>H₂O salt to solutions of ZnS nanoparticles. The postsynthetically treated ZnS nanoparticle systems display Tb³⁺ and Eu³⁺ luminescence intensities that are comparable to those of doped Zn­(Ln)S nanoparticles, which we reported previously (<i>J. Phys. Chem. A</i>, <b>2011</b>, <i>115</i>, 4031–4041). A comparison with the synthetically doped systems is used to contrast the spatial distribution of the lanthanide ions, bulk versus surface localized. The postsynthetic strategy described in this work is fundamentally different from the synthetic incorporation (doping) approach and offers a rapid and less synthetically demanding protocol for Tb³⁺:ZnS and Eu³⁺:ZnS luminophores, thereby facilitating their use in a broad range of applications

Modulating the Bond Strength of DNA–Nanoparticle Superlattices

A method is introduced for modulating the bond strength in DNA–programmable nanoparticle (NP) superlattice crystals. This method utilizes noncovalent interactions between a family of [Ru­(dipyrido­[2,3-<i>a</i>:3′,2′-<i>c</i>]­phenazine)­(N–N)₂]²⁺-based small molecule intercalators and DNA duplexes to postsynthetically modify DNA–NP superlattices. This dramatically increases the strength of the DNA bonds that hold the nanoparticles together, thereby making the superlattices more resistant to thermal degradation. In this work, we systematically investigate the relationship between the structure of the intercalator and its binding affinity for DNA duplexes and determine how this translates to the increased thermal stability of the intercalated superlattices. We find that intercalator charge and steric profile serve as handles that give us a wide range of tunability and control over DNA–NP bond strength, with the resulting crystal lattices retaining their structure at temperatures more than 50 °C above what nonintercalated structures can withstand. This allows us to subject DNA–NP superlattice crystals to conditions under which they would normally melt, enabling the construction of a core–shell (gold NP-quantum dot NP) superlattice crystal

Boron-Dipyrromethene-Functionalized Hemilabile Ligands as “Turn-On” Fluorescent Probes for Coordination Changes in Weak-Link Approach Complexes

Herein we report a new class of hemilabile ligands with boron-dipyrromethene (Bodipy) fluorophores that, when complexed to Pt­(II), can signal changes in coordination mode through changes in their fluorescence. The ligands consist of phosphino-amine or phosphino-thioether coordinating moieties linked to the Bodipy’s meso carbon via a phenylene spacer. Interestingly, this new class of ligands can be used to signal both ligand displacement and chelation reactions in a fluorescence “turn-on” fashion through the choice of weakly binding heteroatom in the hemilabile moiety, generating up to 10-fold fluorescence intensity increases. The Pt­(II) center influences the Bodipy emission efficiency by regulating photoinduced electron transfer between the fluorophore and its meso substituent. The rates at which the excited Bodipy-species generate singlet oxygen upon excitation suggest that the heavy Pt­(II) center also influences Bodipy’s emission efficiency by affecting intersystem crossing from the Bodipy excited singlet to excited triplet states. This signaling strategy provides a quantitative read-out for changes in coordination mode and potentially will enable the design of new molecular systems for sensing and signal amplification

OWL-Based Nanomasks for Preparing Graphene Ribbons with Sub-10 nm Gaps

We report a simple and highly efficient method for creating graphene nanostructures with gaps that can be controlled on the sub-10 nm length scale by utilizing etch masks comprised of electrochemically synthesized multisegmented metal nanowires. This method involves depositing striped nanowires with Au and Ni segments on a graphene-coated substrate, chemically etching the Ni segments, and using a reactive ion etch to remove the graphene not protected by the remaining Au segments. Graphene nanoribbons with gaps as small as 6 nm are fabricated and characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The high level of control afforded by electrochemical synthesis of the nanowires allows us to specify the dimensions of the nanoribbon, as well as the number, location, and size of nanogaps within the nanoribbon. In addition, the generality of this technique is demonstrated by creating silicon nanostructures with nanogaps