Photoinduced Plasmon-Driven Chemistry in trans-1,2-Bis(4-pyridyl)ethylene Gold Nanosphere Oligomers

Transformation of 3D Metal-Organic Frameworks into Nanosheets with Enhanced Memristive Behavior for Electronic Data Processing

The transition from three-dimensional (3D) to two-dimensional (2D) semiconducting and insulating materials for micro- and opto-electronics is driven by an energy efficiency and device miniaturization. Herein, the simplicity of growth and stacking of 2D metal-organic framework (MOF) with such planar devices opens up new perspectives in controlling their efficiency and operating parameters. Here, the study reports on 3D to 2D MOF' structural transformation to achieve ultrathin nanosheets with enhanced insulating properties. Based on neutral N-donor ligands, the study designs and solvothermally synthesizes 3D MOFs followed by their thermal and solvent treatment to implement the transformation. A set of single crystal and powder X-ray diffraction, electron microscopy, Raman spectroscopy, numerical modeling, and mechanical exfoliation confirm the nature of the transformation. Compared with initial 3D MOF, its nanosheets demonstrate sufficient changes in electronic properties, expressed as tuning their absorption, photoluminescence, and resistivity. The latter allows to demonstrate the prototype of ultrathin memristive element based on a 4 to 32 nm MOF nanosheet with enhanced functionality (150 to 1400 ON/OFF ratio, retention time exceeding 7300 s, and 100 cycles of switching), thereby, extending the list of scalable and insulating 2D MOFs for micro- and opto-electronics.

Surface-Enhanced Raman Scattering Sensors Employing a Nanoparticle-On-Liquid-Mirror (NPoLM) Architecture

Surface-enhanced Raman scattering (SERS) sensors typically employ nanophotonic structures that support high-field confinement and enhancement in hotspots to increase the Raman scattering from target molecules by orders of magnitude. In general, high field and SERS enhancement can be achieved by reducing the critical dimensions and mode volumes of the hotspots to nanoscale. To this end, a multitude of SERS sensors employing photonic structures with nanometric hotspots have been demonstrated. However, delivering analyte molecules into nanometric hotspots is challenging, and the trade-off between field confinement/enhancement and analyte delivery efficiency is a critical limiting factor for the performance of many nanophotonic SERS sensors. Here, a new type of SERS sensor employing solid-metal nanoparticles and bulk liquid metal is demonstrated to form nanophotonic resonators with a nanoparticle-on-liquid-mirror (NPoLM) architecture, which effectively resolves this trade-off. In particular, this unconventional sensor architecture allows for the convenient formation of nanometric hotspots by introducing liquid metal after analyte molecules are efficiently delivered to the surface of gold nanoparticles. In addition, a cost-effective and reliable process is developed to produce gold nanoparticles on a substrate suitable for forming NPoLM structures. These NPoLM structures achieve two orders of magnitude higher SERS signals than the gold nanoparticles alone.

Comparison of Gap-Enhanced Raman Tags and Nanoparticle Aggregates with Polarization Dependent Super-Resolution Spectral SERS Imaging

Strongly confined electric fields resulting from nanogaps within nanoparticle aggregates give rise to significant enhancement of surface-enhanced Raman scattering (SERS). Nanometer differences in gap sizes lead to drastically different confined field strengths; so much attention has been focused on the development and understanding of nanostructures with controlled gap sizes. In this work, we report a novel petal gap-enhanced Raman tag (GERT) consisting of a bipyramid core and a nitrothiophenol (NTP) spacer to support the growth of hundreds of small petals and compare its SERS emission and localization to a traditional bipyramid aggregate. To do this, we use super resolution spectral SERS imaging that simultaneously captures the SERS images and spectra while varying the incident laser polarization. Intensity fluctuations inherent of SERS enabled super resolution algorithms to be applied, which revealed subdiffraction limited differences in the localization with respect to polarization direction for both particles. Interestingly, however, only the traditional bipyramid aggregates experienced a strong polarization dependence in their SERS intensity and in the plasmon-induced conversion of NTP to dimercaptoazobenzene (DMAB), which was localized with nanometer precision to regions of intense electromagnetic fields. The lack of polarization dependence (validated through electromagnetic simulations) and surface reactions from the bipyramid-GERTs suggests that the emissions arising from the bipyramid-GERTs are less influenced by confined fields.

Condensed Matter Systems Exposed to Radiation: Multiscale Theory, Simulations, and Experiment

This roadmap reviews the new, highly interdisciplinary research field studying the behavior of condensed matter systems exposed to radiation. The Review highlights several recent advances in the field and provides a roadmap for the development of the field over the next decade. Condensed matter systems exposed to radiation can be inorganic, organic, or biological, finite or infinite, composed of different molecular species or materials, exist in different phases, and operate under different thermodynamic conditions. Many of the key phenomena related to the behavior of irradiated systems are very similar and can be understood based on the same fundamental theoretical principles and computational approaches. The multiscale nature of such phenomena requires the quantitative description of the radiation-induced effects occurring at different spatial and temporal scales, ranging from the atomic to the macroscopic, and the interlinks between such descriptions. The multiscale nature of the effects and the similarity of their manifestation in systems of different origins necessarily bring together different disciplines, such as physics, chemistry, biology, materials science, nanoscience, and biomedical research, demonstrating the numerous interlinks and commonalities between them. This research field is highly relevant to many novel and emerging technologies and medical applications.

Plasmon resonance dynamics and enhancement effects in tris(2,2'-bipyridine)ruthenium(II) gold nanosphere oligomers

Ruthenium-based metal complexes are one of the most widely studied dyes because of their rich photochemistry and light-harvesting properties. Significant attention has been paid to the energy and charge transfer dynamics of these dyes on semiconductor substrates. However, studies on photophysical and photochemical properties of these dyes in plasmonic environments are rare. In this study, we report a plasmon-mediated resonance energy transfer in an optimized oligomer system that enhances the photoexcited population of the well known dye, tris(2,2'-bipyridine)ruthenium(II), [Ru(BPY)3]2+ adsorbed on gold nanosphere surfaces with a defluorescenced Raman signal. Structural and chemical information is collected using a range of techniques that include in situ time-resolved UV/VIS, DLS, SERS, and TA. The findings have great potential to impact nanoscience broadly with special emphasis on surface photocatalysis, redox chemistry, and solar energy harvesting.

Quantifying the ultrafast and steady-state molecular reduction potential of a plasmonic photocatalyst

Plasmonic materials are promising photocatalysts as they are well suited to convert light into hot carriers and heat. Hot electron transfer is suggested as the driving force in many plasmon-driven reactions. However, to date, there are no direct molecular measures of the rate and yield of plasmon-to-molecule electron transfer or energy of these electrons on the timescale of plasmon decay. Here, we use ultrafast and spectroelectrochemical surface-enhanced Raman spectroscopy to quantify electron transfer from a plasmonic substrate to adsorbed methyl viologen molecules. We observe a reduction yield of 2.4 to 3.5% on the picosecond timescale, with plasmon-induced potentials ranging from [Formula: see text]3.1 to [Formula: see text]4.5 mV. Excitingly, some of these reduced species are stabilized and persist for tens of minutes. This work provides concrete metrics toward optimizing material-molecule interactions for efficient plasmon-driven photocatalysis.

Insights into Plasmon-Induced Dimerization of Rhodanine-A Surface-Enhanced Raman Scattering Study

Plasmon-mediated chemical reactions (PMCRs) have attracted considerable interest in recent times. The PMCR initiated by hot carriers is known to be influenced by the type of metals and the excitation wavelength. Herein, we have carried out the surface-enhanced Raman scattering (SERS) investigation of rhodanine (Rd), an important pharmacologically active heterocyclic compound, adsorbed on silver and gold nanoparticles (AgNP and AuNP) using 514.5 and 632.8 nm lasers. The prominent Raman band at 1566 cm^-1 observed in the SERS spectra is attributed to the characteristic ν(C═C) stretching vibration of the Rd dimer and not of Rd tautomers. The chemical transformation of Rd to Rd dimer on metal surfaces is plausibly triggered by the indirect transfer of energetic hot electrons generated during the non-radiative decay of plasmon. The mechanism involved in the dimerization of Rd via the indirect transfer of hot electrons is also presented. The effect of wavelength on the dimerization of Rd is also observed on the AgNP surface, which indicates that the dimerization occurs more efficiently on the AgNP surface with excitation at 514.5 nm wavelength.

Photoexcited Plasmon-Driven Ultrafast Dynamics of the Adsorbate Probed by Femtosecond Time-Resolved Surface-Enhanced Time-Domain Raman Spectroscopy

Metal nanoparticles have high potential in light-harvesting applications by transferring absorbed photon energy to the adsorbates. However, photoexcited plasmon-driven ultrafast dynamics of the adsorbate on metal nanoparticles have not been clearly understood. We studied ultrafast plasmon-driven processes of trans-1,2-bis(4-pyridyl)ethylene (BPE) adsorbed on gold nanoparticle assemblies (GNAs) using time-resolved surface-enhanced impulsive stimulated Raman spectroscopy (TR-SE-ISRS). After photoexciting the localized surface plasmon resonance (LSPR) band of the GNAs, we measured femtosecond time-resolved surface-enhanced Raman spectra of the adsorbate, which exhibited transient bleach in the Raman signal and following biphasic recovery that proceeds on the time scale of a few tens of picoseconds. The TR-SE-ISRS data were analyzed with singular value decomposition, and the obtained species-associated Raman spectra indicated that photoexcitation of the LSPR band alters chemical interaction between BPE and the GNAs on an ultrafast time scale; initial steady-state BPE is recovered through a precursor state that has weaker interaction with the GNAs.

Investigation of SERS Frequency Fluctuations Relevant to Sensing and Catalysis

The excitation of plasmon resonances on nanoparticles generates locally enhanced electric fields commonly used for sensing applications and energetic charge carriers can drive chemical transformations as photocatalysts. The surface-enhanced Raman scattering (SERS) spectra from mercaptobenzoic acid (MBA) adsorbed to gold nanoparticles (AuNP) and silica encapsulated gold nanoparticles (AuNP@silica) can be used to assess the impact of energetic charge carriers on the observed signal. Measurements were recorded using a traditional point focused Raman spectroscopy and a wide-field spectral imaging approach to assess changes in the spectra of the different particles at increasing power density. The wide-field approach provides an increase in sampling statistics and shows evidence of SERS frequency fluctuations from MBA at low power densities, where it is commonly difficult to record spectra from a point focused spot. The increased spectral resolution of the point spectroscopy measurement provides improved peak identification and the ability to correlate the frequency fluctuations to charged intermediate species. Interestingly, our work suggests that isolated nanoparticles may undergo frequency fluctuations more readily than aggregates.

Indirect to Direct Charge Transfer Transition in Plasmon-Enabled CO2 Photoreduction

Understanding hot carrier dynamics between plasmonic nanomaterials and its adsorbate is of great importance for plasmon-enhanced photoelectronic processes such as photocatalysis, optical sensing and spectroscopic analysis. However, it is often challenging to identify specific dominant mechanisms for a given process because of the complex pathways and ultrafast interactive dynamics of the photoelectrons. Here, using CO₂ reduction as an example, the underlying mechanisms of plasmon-driven catalysis at the single-molecule level using time-dependent density functional theory calculations is clearly probed. The CO₂ molecule adsorbed on two typical nanoclusters, Ag₂₀ and Ag₁₄₇ , is photoreduced by optically excited plasmon, accompanied by the excitation of asymmetric stretching and bending modes of CO₂ . A nonlinear relationship has been identified between laser intensity and reaction rate, demonstrating a synergic interplay and transition from indirect hot-electron transfer to direct charge transfer, enacted by strong localized surface plasmons. These findings offer new insights for CO₂ photoreduction and for the design of effective pathways toward highly efficient plasmon-mediated photocatalysis.

Spectrally Resolved Surface-Enhanced Raman Scattering Imaging Reveals Plasmon-Mediated Chemical Transformations

Challenges investigating molecules on plasmonic nanostructures have limited understanding of these interactions. However, the chemically specific information in the surface-enhanced Raman scattering (SERS) spectrum can identify perturbations in the adsorbed molecules to provide insight relevant to applications in sensing, catalysis, and energy conversion. Here, we demonstrate spectrally resolved SERS imaging, to simultaneously image and collect the SERS spectra from molecules adsorbed on individual nanoparticles. We observe intensity and frequency fluctuations in the SERS signal on the time scale of tens of milliseconds from n-mercaptobenzoic acid (MBA) adsorbed to gold nanoparticles. The SERS signal fluctuations correlate with density functional theory calculations of radicals generated by the interaction between MBA and plasmon-generated hot electrons. Applying localization microscopy to the data provides a super-resolution spectrally resolved map that indicates the plasmonic-induced molecular charging occurs on the extremities of the nanoparticles, where the localized electromagnetic field is reported to be most intense.

Tracking interfacial single-molecule pH and binding dynamics via vibrational spectroscopy

Understanding single-molecule chemical dynamics of surface ligands is of critical importance to reveal their individual pathways and, hence, roles in catalysis, which ensemble measurements cannot see. Here, we use a cascaded nano-optics approach that provides sufficient enhancement to enable direct tracking of chemical trajectories of single surface-bound molecules via vibrational spectroscopy. Atomic protrusions are laser-induced within plasmonic nanojunctions to concentrate light to atomic length scales, optically isolating individual molecules. By stabilizing these atomic sites, we unveil single-molecule deprotonation and binding dynamics under ambient conditions. High-speed field-enhanced spectroscopy allows us to monitor chemical switching of a single carboxylic group between three discrete states. Combining this with theoretical calculation identifies reversible proton transfer dynamics (yielding effective single-molecule pH) and switching between molecule-metal coordination states, where the exact chemical pathway depends on the intitial protonation state. These findings open new domains to explore interfacial single-molecule mechanisms and optical manipulation of their reaction pathways.

Cascaded nanooptics to probe microsecond atomic-scale phenomena

Plasmonic nanostructures can focus light far below the diffraction limit, and the nearly thousandfold field enhancements obtained routinely enable few- and single-molecule detection. However, for processes happening on the molecular scale to be tracked with any relevant time resolution, the emission strengths need to be well beyond what current plasmonic devices provide. Here, we develop hybrid nanostructures incorporating both refractive and plasmonic optics, by creating SiO₂ nanospheres fused to plasmonic nanojunctions. Drastic improvements in Raman efficiencies are consistently achieved, with (single-wavelength) emissions reaching 10⁷ counts⋅mW^-1⋅s^-1 and 5 × 10⁵ counts∙mW^-1∙s^-1∙molecule^-1, for enhancement factors >10¹¹ We demonstrate that such high efficiencies indeed enable tracking of single gold atoms and molecules with 17-µs time resolution, more than a thousandfold improvement over conventional high-performance plasmonic devices. Moreover, the obtained (integrated) megahertz count rates rival (even exceed) those of luminescent sources such as single-dye molecules and quantum dots, without bleaching or blinking.

Present and Future of Surface-Enhanced Raman Scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

Plasmon-Induced Dimerization of Thiazolidine-2,4-dione on Silver Nanoparticles: Revealed by Surface-Enhanced Raman Scattering Study

Surface-enhanced Raman scattering (SERS) study carried on thiazolidine-2,4-dione (TZD), a pharmacologically active heterocyclic compound, points to the presence of TZD dimer formed by plasmon-induced dimerization reaction of TZD on the surface of silver nanoparticles (Ag NP) at TZD concentrations of 10^-3 M and above. The evidence for the presence of dimer was obtained from the appearance of a prominent band at 1566 cm^-1 corresponding to the ν(C═C) band (a characteristic vibrational band observed for the Knoevenagel condensation reaction products) which is absent in the normal Raman scattering (NRS) spectra of TZD solid/solution. The observed spectrum compares well with the calculated spectrum of dimer obtained using density functional theory (DFT) calculations. The dimerization reaction is plausibly induced by the transfer of hot electrons generated by the nonradiative plasmon decay of Ag NP, and the proposed reaction mechanism is discussed. However, at lower concentrations (10^-4-10^-6 M), the characteristic dimer peak (1566 cm^-1) is absent and the SERS spectra resemble more the NRS spectrum of TZD with a few changes. The spectral analysis supported by DFT calculations showed that TZD molecules undergo deprotonation and get adsorbed on the Ag NP surface as enolate forms. The proximity of TZD molecules on the surface of Ag NP is a necessary factor for the dimerization to occur. At lower concentrations, most molecules lie apart and reactions between molecules become less feasible, and they remain as monomers on the surface, while at higher concentrations the molecules are closer to each other on the Ag NP surface favoring the dimerization reaction to take place, leading to the formation of the dimer.

Machine Learning Protocol for Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique that can capture the electronic-vibrational "fingerprint" of molecules on surfaces. Ab initio prediction of Raman response is a long-standing challenge because of the diversified interfacial structures. Here we show that a cost-effective machine learning (ML) random forest method can predict SERS signals of a trans-1,2-bis (4-pyridyl) ethylene (BPE) molecule adsorbed on a gold substrate. Using geometric descriptors extracted from quantum chemistry simulations of thousands of ab initio molecular dynamics conformations, the ML protocol predicts vibrational frequencies and Raman intensities. The resulting spectra agree with density functional theory calculations and experiment. Predicted SERS responses of the molecule on different surfaces, or under external fields of electric fields and solvent environment, demonstrate the good transferability of the protocol.

High-speed imaging of surface-enhanced Raman scattering fluctuations from individual nanoparticles

The concept of plasmonic hotspots is central to the interpretation of the surface-enhanced Raman scattering (SERS) effect. Although plasmonic hotspots are generally portrayed as static features, single-molecule SERS (SM-SERS) is marked by characteristic time-dependent fluctuations in signal intensity. The origin of those fluctuations can be assigned to a variety of dynamic and complex processes, including molecular adsorption or desorption, surface diffusion, molecular reorientation and metal surface reconstruction. Since each of these mechanisms simultaneously contributes to a fluctuating SERS signal, probing their relative impact in SM-SERS remains an experimental challenge. Here, we introduce a super-resolution imaging technique with an acquisition rate of 800,000 frames per second to probe the spatial and temporal features of the SM-SERS fluctuations from single silver nanoshells. The technique has a spatial resolution of ~7 nm. The images reveal short ~10 µs scattering events localized in various regions on a single nanoparticle. Remarkably, even a fully functionalized nanoparticle was 'dark' more than 98% of the time. The sporadic SERS emission suggests a transient hotspot formation mechanism driven by a random reconstruction of the metallic surface, an effect that dominates over any plasmonic resonance of the particle itself. Our results provide the SERS community with a high-speed experimental approach to study the fast dynamic properties of SM-SERS hotspots in typical room-temperature experimental conditions, with possible implications in catalysis and sensing.

Plasmon-Enhanced Deuteration under Visible-Light Irradiation

Deuteration has found important applications in synthetic chemistry especially for pharmaceutical developments. However, conventional deuteration methods using transition-metal catalysts or strong bases generally involve harsh reaction conditions, expensive deuterium source, insufficient efficiency, and poor selectivity. Herein, we report an efficient visible-light-driven dehalogenative deuteration of organic halides using plasmonic Au/CdS as photocatalyst and D₂O as deuterium donor. Electron transfer from Au to CdS, which has been confirmed by surface-enhanced Raman spectroscopy, plays a decisive role for the plasmon-mediated dehalogenation. The deuteration is revealed to proceed via a radical pathway in which substrates are first activated by the photoinduced electron transfer to generate aryl radicals, and the radicals are further trapped by D₂O to give deuterated products. Under visible-light irradiation, excellent deuteration efficiency is achieved with high functional group tolerance and a wide range of substrates at room temperature. Compared with bare CdS, the photocatalytic activity increases ∼18 times after the loading of plasmonic Au nanoparticles. This work sheds light on the interfacial charge transfer between plasmonic metals and semiconductors as an important criterion for rational design of visible-light photocatalysts.

Nanoscale Chemical Reaction Imaging at the Solid-Liquid Interface via TERS

Not all regions of optical field nanolocalization and enhancement are suitable sites for chemical transformations on plasmonic metals. We illustrate the concept using chemically functionalized monocrystalline gold platelets in aqueous solution imaged using a Au-coated tip-enhanced Raman scattering (TERS) probe. For our proof-of-principle study, we select a model plasmon-driven chemical process, namely, the dimerization of p-nitrothiophenol (NTP) to dimercaptoazobenzene. Consistent with recent observations from our group, we find that TERS maps at vibrational resonances corresponding to NTP trace the optical fields that are maximally enhanced toward the edges of the platelets. Conversely, simultaneously recorded product maps reveal that the dimerization process occurs only at specific sites on our substrate. Given the uniformity of the structures and local optical fields at the edges of the gold platelets, our results suggest that molecular crowding and steric effects play a key role in our case of plasmon-driven NTP dimerization at the gold-water interface.

In situ detection of trace pollutants: a cost-effective SERS substrate of blackberry-like silver/graphene oxide nanoparticle cluster based on quick self-assembly technology

To realize fast detection of trace hazardous chemicals, a SERS substrate with the structure of a blackberry-like silver/graphene oxide nanoparticle cluster (Ag/GO NPC) has been designed and prepared through a quick capillarity-assistant self-assembly technology in this paper. Benefitting from the abundant "hot spots" and active oxygen sites brought by this Ag/GO NPC, the substrate shows good Raman performance for malachite green (MG), a common abusive germicide in aquaculture, with lowest limit of detection below 0.1 µg/L (3.48 × 10^-10 mol/L). Detailed analyses are taken on both the formation process and enhancement mechanism of this SERS substrate, and the finite-difference time-domain simulations are utilized as well to prove our hypotheses. Further constructing this structure on polyethylene terephthalate (PET) film, a translucent flexible SERS substrate can be obtained, realizing a fast in situ detection of trace MG in the fishpond subsequently. In consideration of the facile preparation process, good SERS enhancement and affordable materials (PET, Cu, Ag and GO, etc.), this substrate presents high cost performance and a promising application prospect.

Broad-band high-gain room temperature photodetectors using semiconductor-metal nanofloret hybrids with wide plasmonic response

Semiconducting nanowires are widely studied as building blocks for electro-optical devices; however, their limited cross-section and hence photo-response hinder the utilization of their full potential. Herein, we present an opto-electronic device for broad spectral detection ranging from the visible (VIS) to the short wavelength infra-red (SWIR) regime, using SiGe nanowires coupled to a broadband plasmonic antenna. The plasmonic amplification is obtained by deposition of a metallic nanotip at the edge of a nanowire utilizing a bottom-up synthesis technique. The metallic nanotip is positioned such that both optical plasmonic modes and electrical detection paths are coupled, resulting in a specific detectivity improvement of ∼1000 compared to conventional SiGe NWs. Detectivity and high gain are also measured in the SWIR regime owing to the special plasmonic response. Furthermore, the temporal response is improved by ∼1000. The fabrication process is simple and scalable, and it relies on low-resolution and facile fabrication steps with minimal requirements for top-down techniques.

Chiral Plasmonic Nanocrystals for Generation of Hot Electrons: Toward Polarization-Sensitive Photochemistry

The use of biomaterials, with techniques such as DNA-directed assembly or biodirected synthesis, can surpass top-down fabrication techniques in creating plasmonic superstructures in terms of spatial resolution, range of functionality, and fabrication speed. In particular, by enabling a very precise placement of nanoparticles in a bioassembled complex or through the controlled biodirected shaping of single nanoparticles, plasmonic nanocrystals can show remarkably strong circular dichroism (CD) signals. We show that chiral bioplasmonic assemblies and single nanocrystals can enable polarization-sensitive photochemistry based on the generation of energetic (hot) electrons. It is now established that hot plasmonic electrons can induce surface photochemistry or even reshape plasmonic nanocrystals. We show that merging chiral plasmonic nanocrystal systems and the hot-election generation effect offers unique possibilities in photochemistry, such as polarization-sensitive photochemistry promoting nonchiral molecular reactions, chiral photoinduced growth of a colloid at the atomic level, and chiral photochemical destruction of chiral nanocrystals. In contrast, for chiral molecular systems, the equivalent of the described effects is challenging to observe because molecular species typically exhibit very small CD signals. Moreover, we compare our findings with traditional chiral photochemistry at the molecular level, identifying new, different regimes for chiral photochemistry with possibilities that are unique for plasmonic colloidal systems. In this study, we bring together the concept of hot-electron generation and the field of chiral colloidal plasmonics. Using chiral plasmonic nanorod complexes as a model system, we demonstrate remarkably strong CD in both optical extinction and generation rates of hot electrons. Studying the regime of steady-state excitation, we discuss the influence of geometrical and material parameters on the chiral effects involved in the generation of hot electrons. Optical chirality and the chiral hot-electron response in the nanorod dimers result from complex interparticle interactions, which can appear in the weak coupling regime or in the form of Rabi splitting. Regarding practical applications, our study suggests interesting opportunities in polarization-sensitive photochemistry, in chiral recognition or separation, and in promoting chiral crystal growth at the nanoscale.

Modulating and probing the dynamic intermolecular interactions in plasmonic molecule-pair junctions

The intermolecular interactions, including hydrogen bonds, are electromechanically modulated and probed in metal–molecule pair–metal junctions.

Ambient electrospray deposition Raman spectroscopy (AESD RS) using soft landed preformed silver nanoparticles for rapid and sensitive analysis

Ambient electrospray deposition Raman spectroscopy (AESD RS) using soft landed preformed silver nanoparticles for rapid and sensitive SERS analysis.

Plasmon-Driven Photocatalysis Leads to Products Known from E-beam and X-ray-Induced Surface Chemistry

Plasmonic metal nanostructures can concentrate incident optical fields in nanometer-sized volumes, called hot spots. This leads to enhanced optical responses of molecules in such a hot spot but also to chemical transformations, driven by plasmon-induced hot carriers. Here, we employ tip-enhanced Raman spectroscopy (TERS) to study the mechanism of these reactions in situ at the level of a single hot spot. Direct spectroscopic measurements reveal the energy distribution of hot electrons, as well as the temperature changes due to plasmonic heating. Therefore, charge-driven reactions can be distinguished from thermal reaction pathways. The products of the hot-carrier-driven reactions are strikingly similar to the ones known from X-ray or e-beam-induced surface chemistry despite the >100-fold energy difference between visible and X-ray photons. Understanding the analogies between those two scenarios implies new strategies for rational design of plasmonic photocatalytic reactions and for the elimination of photoinduced damage in plasmon-enhanced spectroscopy.