Carbon Dioxide-Derived <i>Immortal</i> Brush Macromolecules with Poly(propylene carbonate) Side Chains

Brush macromolecules (BMs) are unique because of their distinct properties from linear or other nonlinear polymers, relying on side chain steric repulsions and backbone stiffness. BMs with densely grafted side chains have been synthesized either by cationic, anionic, or controlled radical polymerization, yet CO₂–epoxide <i>immortal</i> alternating copolymerization has rarely been applied for the synthesis of BMs via the “grafting-from” approach. Here we report synthesis of BMs by alternating copolymerization of CO₂ and propylene oxide (PO) initiated from poly­(acrylic acid) as a multifunctional macroinitiator. The copolymerization afforded ultrahigh-molecular-weight BMs with poly­(propylene carbonate) (PPC) side chains (molecular weight >10⁶), and the side chain length was tunable via further CO₂–PO alternating copolymerization initiated from hydroxy end groups of the resulting side chain PPCs. These BMs were directly observed by atomic force microscopy, demonstrating that the BMs have ellipsoidal morphologies with 20–50 nm. Furthermore, the BMs were thermally decomposable at around 240 °C

Broadband Dielectric–Metal Hybrid Nanoantenna: Silicon Nanoparticle on a Mirror

We developed a broadband dielectric–metal hybrid nanogap resonator composed of a silicon nanoparticle (Si NP) and gold (Au) flat surface. We fabricate the nanogap resonator by depositing a monolayer of colloidal quantum dots (QDs) (∼2.8 nm in diameter) on a Au surface followed by dropping a diluted colloidal solution of Si NPs (∼150 nm in diameter). The QD monolayer acts as a precisely length-controlled nanogap as well as a light emitter to monitor the radiative properties of the nanogap resonator. We investigate the light-scattering properties of single-nanogap resonators experimentally and theoretically and found that the coupling of the Mie resonance of Si NPs with a Au surface effectively confines the electromagnetic field into the nanogap in a wider wavelength range than an all-metal nanogap resonator with a comparable size. Furthermore, we show that the resonance wavelength of the hybrid nanogap resonator is less sensitive to the gap length than that of the all-metal one. We demonstrate that the broadband hybrid nanogap resonator enhances photoluminescence of a QD monolayer integrated in the nanogap by a factor of 786

Absolute Scattering Cross Sections of Titanium Nitride Nanoparticles Determined by Single-Particle Spectroscopy: Implications for Plasmonic Nanoantennas

Titanium nitride (TiN) nanostructures are promising building blocks for photothermal applications because of the surface plasmon-induced light absorption. However, compared to noble metal nanostructures, detailed analyses of the plasmonic responses of TiN nanostructures have been limited. In this work, by combining transmission electron microscopy (TEM) and single-particle spectroscopy, we determine absolute scattering cross sections of individual TiN nanocubes (NCs). The key aspect of the developed methodology is placing a TiN NC on an ultrathin SiO2 membrane and performing the precise structural analysis and the scattering spectrum measurement on the same TiN NCs. Furthermore, by employing Au nanospheres as references, we quantitatively compare the scattering spectra with those obtained for TiN NCs and determine the absolute scattering cross section as a function of NC size

Dual Catalyst System for Asymmetric Alternating Copolymerization of Carbon Dioxide and Cyclohexene Oxide with Chiral Aluminum Complexes: Lewis Base as Catalyst Activator and Lewis Acid as Monomer Activator

Optically active aluminum complexes such as Schiff base, binuclear β-ketoiminate, and bisprolinol complexes were found to promote asymmetric alternating copolymerizations of carbon dioxide and cyclohexene oxide. The aluminum Schiff base complexes–tetraethylammonium acetate afforded isotactic poly­(cyclohexene carbonate)­s with low enantioselectivities. Lewis bases having two coordinating sites were utilized to enhance activity and selectivity based on the binuclear structure of the aluminum β-ketoiminate clarified by X-ray crystallography. [<b>2g</b>AlMe]₂–bulky bisimidazole produced the alternating copolymer with high enantioselectivity (62% ee). The polymerization is considered to preferentially proceed at more crowded, enantioselective site owing to coordination of bulky Lewis bases to aluminums in less enantioselective sites. <b>3</b>₂AlMe–2-picoline also exhibited a high enantioselectivity (67% ee). Methylaluminum bis­(2,6-di-<i>tert</i>-butyl-4-methylphenoxide) was applied to perform faster and more enantioselective copolymerizations at low temperature (82% ee). The asymmetric copolymerizations were found to be significantly dependent on size of epoxide, temperature, and kind/amount of activators

Controlling Energy Transfer in Silicon Quantum Dot Assemblies Made from All-Inorganic Colloidal Silicon Quantum Dots

The optical response of an assembly of semiconductor quantum dots (QDs) is strongly modified from those of isolated ones by the inter-QD coupling. The strength of the coupling depends on the size, the inter-QD distance and the number of interacting QDs. In this work, we control these parameters of silicon (Si) QD assemblies by layer-by-layer growth of all-inorganic colloidal Si QDs. We perform detailed photoluminescence (PL) and PL decay dynamics studies for the assemblies made from monolayers of Si QDs 3.0 and 6.8 nm in diameters by precisely controlling the interlayer distance and the number of layers. From the analysis of the data with the Förster resonance energy transfer (FRET) model, we quantitatively discuss the relation between the FRET efficiency and the Förster radius in Si QD assemblies

Size-Dependent Mutual Charge Transfer between B- and P‑Codoped Si Quantum Dots and Monolayer MoS₂

Heterostructures built from two-dimensional (2D) transition metal dichalcogenide (TMD) monolayers and quantum dots (0D) offer a large variety of systems for probing the fundamental physics and for the device applications. In this work, 2D/0D heterostructures comprised of monolayer MoS2 (1L-MoS2) and Si quantum dots (QDs) are produced and the mutual charge transfer is studied. It is shown that the charge transfer property depends strongly on the size of Si QDs. Decoration of a 1L-MoS2 flake with Si QDs with a diameter of 3.5 nm results in the quenching of the PL, while the decoration with Si QDs with a diameter of 9.0 nm enhances it. The results indicate that the direction of the charge transfer is different depending on the Si QD diameter. Contributions of the A excitons, B excitons, biexcitons, and trions to the total PL spectra are analyzed in a wide excitation power range, and the mechanism of the charge transfer is discussed

Hybridized Plasmonic Gap Mode of Gold Nanorod on Mirror Nanoantenna for Spectrally Tailored Fluorescence Enhancement

Plasmonic nanoparticle on mirror antennas with sub-10 nm gaps have shown the great potential in nanophotonic applications because they offer tightly confined electric field in the gap and resultant large Purcell factors. However, in a nanosphere on mirror (NSoM) structure being studied experimentally, the degree of freedom of the antennas in terms of spectral and polarization control is limited. In this work, we report spectral shaping and polarization control of Purcell-enhanced fluorescence by the gap plasmon modes of an anisotropic gold (Au) nanorod on a mirror (NRoM) antenna. Systematic numerical calculations demonstrate the richer resonance behaviors of a NRoM antenna than a NSoM antenna due to the hybridization of the bright and dark modes. We fabricate a NRoM antenna by placing a Au NR on an ultraflat Au film via a mono-, double-, or quadruple-layers of light emitting quantum dots (QDs) (3 nm in diameter). The scattering spectra of single NRoM antennas coincide very well with those of the numerical simulations. We demonstrate large enhancement (>900-fold) and strong shaping of the luminescence from QDs in the gap due to the coupling with the hybridized mode of a NRoM antenna. We also show that the polarization property of the emission is controlled by that of the mode coupled

Dual Catalyst System for Asymmetric Alternating Copolymerization of Carbon Dioxide and Cyclohexene Oxide with Chiral Aluminum Complexes: Lewis Base as Catalyst Activator and Lewis Acid as Monomer Activator

Optically active aluminum complexes such as Schiff base, binuclear β-ketoiminate, and bisprolinol complexes were found to promote asymmetric alternating copolymerizations of carbon dioxide and cyclohexene oxide. The aluminum Schiff base complexes–tetraethylammonium acetate afforded isotactic poly­(cyclohexene carbonate)­s with low enantioselectivities. Lewis bases having two coordinating sites were utilized to enhance activity and selectivity based on the binuclear structure of the aluminum β-ketoiminate clarified by X-ray crystallography. [2gAlMe]2–bulky bisimidazole produced the alternating copolymer with high enantioselectivity (62% ee). The polymerization is considered to preferentially proceed at more crowded, enantioselective site owing to coordination of bulky Lewis bases to aluminums in less enantioselective sites. 32AlMe–2-picoline also exhibited a high enantioselectivity (67% ee). Methylaluminum bis­(2,6-di-tert-butyl-4-methylphenoxide) was applied to perform faster and more enantioselective copolymerizations at low temperature (82% ee). The asymmetric copolymerizations were found to be significantly dependent on size of epoxide, temperature, and kind/amount of activators

Metal-Core/Dielectric-Shell/Metal-Cap Composite Nanoparticle for Upconversion Enhancement

We have developed an upconversion composite nanoparticle composed of a metal core, an upconversion shell, and a metal cap. Numerical simulation of the nanocomposite revealed that hybridization of the localized surface plasmon modes of the core and the cap results in the emergence of novel bonding and antibonding modes. The latter mode has wide tunability in the resonance wavelength and strong field confinement at the position of the upconversion shell. For the fabrication of the composite nanoparticle, we developed a process that combines liquid-phase synthesis and vapor deposition processes. The scattering spectra of single composite nanoparticles agreed well with those in the numerical simulation. The comparison of the upconversion intensity between the metal-core/dielectric-shell structure and the metal-core/dielectric-shell/metal-cap structure revealed that the cap formation increases the intensity several folds

Charge Transfer-Induced Photobrightening of Silicon Quantum Dots in Water Containing a Molecular Reductant

The effect of molecular reductants on the charge transfer-induced brightening of near-infrared photoluminescence (PL) from silicon (Si) quantum dots (QDs) was studied. Without a molecular reductant, a temporal decrease of the PL quantum yield (QY) during light irradiation in water was observed. The temporal photodarkening was reversed when a molecular reductant [sodium sulfites (Na2SO3)] was added in water. In Na2SO3-dissolved water, the PL QY increased gradually during light irradiation. The photobrightening behavior depended strongly on the amount of reductant molecules, excitation power, and the size of Si QDs. The observed phenomena suggest that an excess hole generated by trapping a photoexcited electron to a trap level is effectively removed by a reductant molecule. The observed charge transfer-induced photobrightening paves way to realize high efficiency and stable Si QDs-based phosphors usable in aqueous media