Magnetic Bistability in an Organic Radical-Based Charge Transfer Cocrystal.

We report herein an organic charge transfer cocrystal complex, consisting of a stable radical TPVr and an electron acceptor TCNQF4, as a rare sort of all-organic-based magnetic bistable materials with a thermally activated magnetic hysteresis loop over the temperature range from 170 to 260 K. Detailed X-ray crystallographic studies and theoretical calculations revealed that while a π-associated radical anion dimer was formed upon an integer charge transfer process from TPVr to the TCNQF4 molecules within the cocrystal lattice, the resulting TCNQF4·- π-dimers were found to exhibit varied intradimer π-stacking distances and singly occupied molecular orbital overlaps at different temperatures, thus yielding two different singlet states with distinct singlet-triplet gaps above and below the loop, which eventually contributed to the thermally excited molecular magnetic bistability.

Seedless Synthesis of Monodispersed Gold Nanorods with Remarkably High Yield: Synergistic Effect of Template Modification and Growth Kinetics Regulation.

Gold nanorods (AuNRs) are versatile materials due to their broadly tunable optical properties associated with their anisotropic feature. Conventional seed-mediated synthesis is, however, not only limited by the operational complexity and over-sensitivity towards subtle changes of experimental conditions but also suffers from low yield (≈15 %). A facile seedless method is reported to overcome these challenges. Monodispersed AuNRs with high yield (≈100 %) and highly adjustable longitudinal surface plasmon resonance (LSPR) are reproducibly synthesized. The parameters that influence the AuNRs growth were thoroughly investigated in terms of growth kinetics and soft-template regulation, offering a better understanding of the template-based mechanism. The facile synthesis, broad tunability of LSRP, high reproducibility, high yield, and ease of scale-up make this method promising for the future mass production of monodispersed AuNRs for applications in catalysis, sensing, and biomedicine.

The characteristic Ag(core)Au(shell) nanoparticles as SERS substrates in detecting dopamine molecules at various pH ranges.

AgcoreAushell nanoparticles (NPs) are a promising surface-enhanced Raman scattering (SERS) substrate, which can offer a high enhancement factor through the combined effect of the high SERS activity of the Ag core and the biocompatibility of the Au shell. In this study, AgcoreAushell NPs were examined as SERS substrates for the sensitive detection of dopamine (DA) molecules in an aqueous solution. The SERS activity of the AgcoreAushell NPs was strongly dependent on the pH of the solution. When the pH of the solution was acidic (pH <5) or basic (pH >9), the AgcoreAushell NPs exhibited negligible SERS activity toward the DA molecules, due to the weakened interactions (or repulsive forces) between the DA molecules and the core-shell NPs. On the other hand, the AgcoreAushell NPs exhibited a high SERS activity in the intermediate pH ranges (pH 7-9), due to the molecular bridging effect of DA molecules, which allows probe molecules to be located at the interstitial junctions (so-called hot spots) between the core-shell NPs. The results of this study highlight the importance of probe-induced clustering of core-shell NPs in the SERS measurements at physiological pH.

Optical properties of dopamine molecules with silver nanoparticles as surface-enhanced raman scattering (SERS) substrates at different pH conditions.

Silver nanoparticles (Ag NPs) prepared by the citrate reduction method were examined as surface-enhanced Raman scattering (SERS) substrates in the detection of dopamine (DA) molecules at different hydrogen ion concentrations. The aggregation of Ag NPs was influenced by the crosslinking effect of DA molecules as the function of pH of colloidal solution. Somewhat clustering of Ag NPs in a limited pH range (pH 7-9) exhibited the strong red-shift of absorption peak and maximal SERS activity to DA molecules, highlighting the importance of strong electrostatic adsorption and cross-linking effect that allowed DA molecules to reside in the junctions (hot spots) between aggregated Ag NPs. Furthermore, Ag NPs with DA molecules at strongly basic condition (> pH 9) exhibited the relatively high SERS activity as compared to negligible SERS activity at acidic condition (< or = pH 5), indicating the important role of oxidized surface of silver NPs which can interact with hydroxyl groups of DA molecules.

The optical properties of gold nanoparticles with dopamine at different hydrogen ion concentration.

In this work, gold nanoparticles (Au NPs) were prepared by citrate reduction method, and the Surface-Enhanced Raman Scattering (SERS) intensities of these colloidal solutions with dopamine (DA) were compared at different hydrogen ion concentration (pH). The charged states of Au NPs and DA molecules at different pH were critical factors for the SERS intensity by affecting NPs aggregation degree via DA bridging-effect. The results showed that the SERS enhancement was strongest at intermediate pH ranges (pH 7-9), in which the Au NPs was sufficiently stable and the electrostatic interaction between the Au NPs and the DA molecules was appropriate, together with a slightly aggregating.

Influence of dopamine concentration and surface coverage of Au shell on the optical properties of Au, Ag, and Ag(core)Au(shell) nanoparticles.

Gold (Au), silver (Ag), and Ag(core)Au(shell) nanoparticles (NPs) were explored as optical sensing agents for the sensitive detection of dopamine (DA) neurotransmitters in surface-enhanced Raman scattering (SERS) measurements. In these colloidal systems, dopamine (DA) molecules played as a cross-linker between M NPs (Au or Ag NPs), allowing them to reside in the confined junctions (i.e., hot spots) between aggregated NPs. The progressive addition of DA molecules (from 1 × 10(-6) to 1 × 10(-3) M) consequently decreased a primary absorption peak attributed to the characteristic M NPs and generated a secondary absorption peak at longer wavelengths attributed to heavily aggregated M NPs formed by molecular bridging effects of DA molecules at high concentrations. The aggregation degree of M NPs was also dependent on the surface states of Au and Ag NPs, i.e., DA molecules with positive amine groups induced more aggregations of Au NPs in comparison to Ag NPs with less negative charges. As the final outcome, Au NPs demonstrated higher sensitivity in SERS detection of DA at low concentrations (1 × 10(-7) to 1 × 10(-5) M), whereas Ag NPs exhibited the stronger Raman signals of DA molecules at high concentrations (1 × 10(-4) to 1 × 10(-3) M). Besides, Ag(core)Au(shell) NPs with the lowest surface coverage of Au shell exhibited more sensitive and stronger SERS activity for DA molecules than that of singular Au NPs, probably due to the combined contribution by Ag core with strong SERS intensity and Au shell with high SERS sensitivity.