Multicolor Electrochromic Devices Based on Molecular Plasmonics

Polycyclic aromatic hydrocarbon (PAH) molecules, the hydrogen-terminated, sub-nanometer-scale version of graphene, support plasmon resonances with the addition or removal of a single electron. Typically colorless when neutral, they are transformed into vivid optical absorbers in either their positively or negatively charged states. Here, we demonstrate a low-voltage, multistate electrochromic device based on PAH plasmon resonances that can be reversibly switched between nearly colorless (0 V), olive (+4 V), and royal blue (−3.5 V). The device exhibits highly efficient color change compared to electrochromic polymers and metal oxides, lower power consumption than liquid crystals, and is shown to reversibly switch for at least 100 cycles. We also demonstrate the additive property of molecular plasmon resonances in a single-layer device to display a reversible, transmissive-to-black device. This work illuminates the potential of PAH molecular plasmonics for the development of color displays and large-area color-changing applications due to their processability and ultralow power consumption

Molecular Plasmon–Phonon Coupling

Charged polycyclic aromatic hydrocarbons (PAHs), ultrasmall analogs of hydrogen-terminated graphene consisting of only a few fused aromatic carbon rings, have been shown to possess molecular plasmon resonances in the visible region of the spectrum. Unlike larger nanostructures, the PAH absorption spectra reveal rich, highly structured spectral features due to the coupling of the molecular plasmons with the vibrations of the molecule. Here, we examine this molecular plasmon–phonon interaction using a quantum mechanical approach based on the Franck–Condon approximation. We show that an independent boson model can be used to describe the complex features of the PAH absorption spectra, yielding an analytical and semiquantitative description of their spectral features. This investigation provides an initial insight into the coupling of fundamental excitationsplasmons and phononsin molecules

Molecular Plasmonics

Graphene supports surface plasmons that have been observed to be both electrically and geometrically tunable in the mid- to far-infrared spectral regions. In particular, it has been demonstrated that graphene plasmons can be tuned across a wide spectral range spanning from the mid-infrared to the terahertz. The identification of a general class of plasmonic excitations in systems containing only a few dozen atoms permits us to extend this versatility into the visible and ultraviolet. As appealing as this extension might be for active nanoscale manipulation of visible light, its realization constitutes a formidable technical challenge. We experimentally demonstrate the existence of molecular plasmon resonances in the visible for ionized polycyclic aromatic hydrocarbons (PAHs), which we reversibly switch by adding, then removing, a single electron from the molecule. The charged PAHs display intense absorption in the visible regime with electrical and geometrical tunability analogous to the plasmonic resonances of much larger nanographene systems. Finally, we also use the switchable molecular plasmon in anthracene to demonstrate a proof-of-concept low-voltage electrochromic device

Revealing the Size Effect of Ceria Nanocube-Supported Platinum Nanoparticles in Complete Propane Oxidation

The elimination of propane is one of the key tasks in reducing volatile organic compounds (VOCs) and automotive exhaust emissions. The platinum nanoparticle (NP) is a promising catalyst for propane oxidation, while the study of its structural characteristics and functionality remains in its infancy. In this work, we synthesized the nanocubes CeO2 with a well-defined (100) facet supporting Pt NPs with various sizes, from 1.3 to 7 nm, and systematically investigated the effect of the Pt size on complete propane oxidation efficiency. In particular, CeO2(100) supported Pt NPs smaller than 4 nm promote the formation of positively charged Pt sites, which hinder the adsorption and activation of propane and reduce the intrinsic activity for propane oxidation. Consequently, within this size range, the catalytic performance is primarily influenced by the electronic state of the Pt species, with metallic Pt being identified as the active site for the reaction. Conversely, as the particle size exceeds 4 nm, metallic Pt particles become dominant and the geometric structure starts to influence the activity as well. Such entanglement of electronic and geometric factors gives rise to a volcano relationship between reaction rates and Pt particle sizes ranging from 1.3 to 7 nm, while an increased correlation can be observed between the turnover frequencies and the particle sizes in this range. This knowledge can guide the synthesis of highly active catalysts, enabling the efficient oxidation of VOCs with reduced precious metal loadings