Here, we report plasmonic metamolecules with dynamically controllable optical magnetism. A dynamic metamolecule (DMM) is constructed by decorating gold or silver nanobeads on a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel sphere, which generates uniform coresatellite-type assembly structures with an interbead distance, allowing for strong interparticle coupling. Experimental and simulation results revealed strong magnetic dipole and quadrupole modes observable in the far field both for gold and silver DMMs when the temperature was set above the lower critical solution temperature (LCST) of PNIPAM. Interestingly, gold DMMs showed stronger and more pronounced magnetic resonances than silver DMMs, despite the general notion that silver nanostructures possess superior plasmonic properties. The strong magnetic coupling and structural uniformity along with the ability to dynamically control the assembly structure allowed us to probe distinct optical magnetism in gold and silver and experimentally observe magnetic quadrupole in solution-phase metamolecules for the first time.

It is important but remains a challenge to develop solution-processed plasmonic solar thermoelectricity films on various substrates, without strictly considering hierarchical plasmonic-dielectric-metal structures, to harvest a wide range of visible to near-infrared sunlight. We simply fabricate plasmonic silica metastructure sunlight-collecting nanofilms on highly reflective Cu and Si surfaces by introducing spin coating (with an Ag and silica colloidal mixture, a spin coater, and a heating plate) and low-temperature annealing (in an oven at 200 °C for 1 h) processes. The approximately 250 nm thick metastructure consists of a top 60 nm thick silica layer as an antireflective film and a bottom 190 nm thick Ag nanoparticle-silica hybrid film as a sunlight harvester. The metastructure film reduces the reflectivity of Cu (>90%) and Si (25-35%) to less than 5% at visible to near-infrared frequencies. The metastructure film on the Cu sheet has an absorptance of 0.95 and a thermal emittance of 0.06, ideal for high-performance sunlight absorbers. The solar thermoelectric powers of the film-coated Cu and Si are 15.4 and 4.7 times those of the uncoated Cu and Si substrates, respectively. The metastructure film on Cu exhibited a similar or slightly higher performance than that of a top-class vapor-deposited commercialized absorber film on Cu, demonstrating the robustness of the present method.

Smart windows can change their optical characteristics according to environmental conditions or external stimuli (such as heat and electricity). They are manufactured by considering building characteristics, regional climate, energy policies, and indoor air conditions. Their key optical properties have been improved by developing novel materials, fabrication methods, and designs. The optical properties can be further improved by developing multi‐stimuli‐responsive smart window systems. Recently, some smart windows have been integrated with energy storage, solar energy harvesting, self‐cleaning, and air‐purifying functions. The energy consumed by buildings and houses accounts for a considerable portion of the total energy consumed by a country as well as the world; therefore, these state‐of‐the‐art smart windows will greatly contribute to saving energy. Moreover, some multi‐functional smart windows can help in addressing environmental challenges. This mini‐review particularly focuses on discussing the recent advances made in multi‐stimuli‐responsive and multi‐functional smart windows, in addition to summarizing the researches on electrochromic, thermochromic, and other types of smart windows.

Dynamic metamolecules (DMMs) are composed of a hydrogel dielectric core surrounded by randomly packed plasmonic nanobeads. The optical properties of DMMs can be tuned by controlling their core diameter using temperature variations. We have recently shown that DMMs display strong optical magnetism, including magnetic dipole and magnetic quadrupole resonances, offering significant potential for novel applications. Here, we use a T-matrix approach to characterize the magnetic multipole resonance modes of model metamolecules and explore their presence in experimental data. We show that high-order multipole resonances become prominent as the nanobead or the overall structure size is increased and when the interbead gap is decreased. In this limit, mode mixing among high-order magnetic multipole modes also becomes significant, particularly in the directional scattering spectra. We discuss trends in magnetic scattering observed in both experiments and simulations and provide suggestions for the experimental design and verification of high-order optical magnetic resonances using forward and backward scattering measurements. In addition, we show that the angular scattering of higher-order magnetic modes can display Fano-like interference patterns, which should also be experimentally detectable.