Shell-isolated nanoparticle-enhanced femtosecond stimulated Raman spectroscopy reveals ultrafast molecular dynamics of surface reactions

Domain: physics
Published: 2025-12-13
Editorial outcome: major_revision

Abstract
In-situ tracking of the transient processes of surface/interfacial chemical reactions is of great significance for understanding the essence of catalytic mechanisms but remains highly challenging. Herein, shell-isolated nanoparticle-enhanced femtosecond stimulated Raman spectroscopy (SHINE-FSRS) with high sensitivity and temporal resolution has been developed to explore the ultrafast molecular dynamics of surface reactions. The FSRS signals have been greatly enhanced through the fabrication of plasmonic nanocavities, achieving a maximum enhancement factor of ~106 through optimal matching of the plasmonic band of the nanocavity with the wavelength of the Raman pump laser, using malachite green (MG) as the probe molecule. Using SHINE-FSRS, the ultrafast structural evolution during the photo-induced reaction of malachite green molecules adsorbed on Au or Ag surfaces has been successfully in-situ monitored at the femtosecond timescale. Direct spectroscopic evidence reveals that malachite green undergoes intramolecular twisting with 100 fs, and the strong localized plasmonic field can accelerate the twisting process. This work showcases the capability of SHINE-FSRS to effectively probe the molecular structural evolution of surface species during reactions with high temporal resolution, underscoring its potential for in-situ investigations of surface and interfacial catalytic processes.

Introduction
In-situ monitoring of the dynamic processes of chemical reactions dynamic study, especially in detecting the key intermediates and identifying the molecular structure of key reaction intermediates are of great significance for elucidating molecular reaction mechanisms1–4. Normal Raman spectroscopy5 or infrared spectroscopy (IR)6 is a versatile tool to reveal the fingerprint structures of steady species, but is often frustrated for the dynamic study, especially in detecting the key intermediates within extremely short lifetimes (from femtoseconds to nanoseconds). The transient absorption (TA) spectroscopy7,8 can capture the electronic relative process with temporal resolution up to femtoseconds, but it still remains a significant challenge to reveal the molecular structures of short-lived intermediates.

With the development of femtosecond laser technology, femtosecond stimulated Raman spectroscopy (FSRS)9,10 has emerged as a powerful vibrational spectroscopy. In FSRS, the temporal overlap between Raman pump and probe pulses (typically, a femtosecond white light continuum (WLC)) creates the population at the vibrational excited state and slices the target dynamics with femtosecond temporal resolution firstly. Then the picosecond Raman pump reads out the vibration population at the following process and provides a high-frequency resolution11,12. Thus, high temporal and frequency resolution can be achieved simultaneously with the measurement at different delays13,14. FSRS can reveal molecular structures and properties, such as the magnitude of the bond strengths, the nature of chemical environments, and even the characteristics of the electronically excited state9,15,16. By employing the pump-probe technique, FSRS represents a fundamental advancement in the quest for real-time structural measurements of chemical transformations17–19.

To further improve the sensitivity and generality of Raman spectroscopy, our group invented a technique named shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)20,21. The underlying principle of SHINERS involves chemically coating an ultra-thin (~2 nm) silica shell onto gold nanoparticles (Au NPs), creating shell-isolated nanoparticles (SHINs)22–24. The Au core can generate strong localized electromagnetic fields to amplify the Raman signals of molecules near SHINs, while the silica shell serves as a chemical protector that isolates the Au core from the external environment. This design preserves the enhancement effect while avoiding the charge exchange between Au and its surroundings25. Such a shell-isolated enhanced mode has also been successfully expanded to other techniques to improve their sensitivity26, such as tip-enhanced Raman spectroscopy, sum frequency generation, second harmonic generation, fluorescence, and even mass spectrometry27–30.

Herein, we developed shell-isolated nanoparticle-enhanced femtosecond stimulated Raman spectroscopy (SHINE-FSRS) with ultrahigh sensitivity and temporal resolution by combining SHINERS and FSRS, and achieved the in-situ monitoring of the ultrafast molecular dynamics of surface reactions (Fig. 1a, b). Meanwhile, Raman-induced Kerr effect (RIKE) spectroscopy has been adopted to address the limitations of traditional FSRS, such as dispersive line shapes31,32 and intense probe background. The correlation between the Raman enhancement and excitation wavelengths has been explored in a home-built FSRS setup (Fig. 1c), and a maximum Raman enhancement factor of ~106 has been obtained for various probe molecules when the excitation wavelength matches with the plasmonic band of SHINs. Using the SHINE-FSRS, we monitored ultrafast dynamics of photo-induced process of MG molecule adsorbed on Au surfaces. It is found that the MG molecule would undergo intramolecular twisting within 100 fs, and the strong localized plasmonic field can accelerate the structural evolution process.

Results
Development of SHINE-FSRS methodology
Here, we propose a SHINE-FSRS method by combining SHINERS with FSRS (Fig. 1a–c). RIKE has been introduced by employing a circularly polarized Raman pump via a quarter-wave plate and crossed polarizers in the probe path (Fig. 1c)33–36. A polarizer, half-wave plate, and quarter-wave plate (fixed at 45°) in the Raman pump path generate circularly polarized light, enabling crossed polarizers to suppress ~99% of the probe background while preserving the Raman signal via the Kerr effect. This configuration not only eliminates the white light interference, allowing extended integration for detecting the weak interfacial signals, but also circumvents the dispersive line profiles inherent in conventional FSRS37, thereby facilitating the acquisition of symmetric vibrational spectra with an enhanced signal-to-noise ratio (Supplementary Fig. 1). Meanwhile, we implemented a chopper–Galvo synchronized system that spatially and temporally isolates pump-on/off signals through 1 kHz modulation coupled with probe beam dithering. Time-resolved Raman spectra were acquired using a normalized differential approach; by subtracting the Raman spectrum without the 400 nm pump pulse from that with the pump pulse at specific time delays (Fig. 1c).

We deposited ~20 nm Au film on a quartz wafer as the substrate of sample, so that it can transmit light while generating surface plasmon resonance (SPR). SHINs with a shell thickness of ~2 nm were self-assembled to form a mono-layer on the Au film adsorbed with probe molecules (Fig. 1d, e). Under light irradiation with a specific wavelength, the Au SHINs can generate a strongly coupling effect with SPR generated on the Au film, significantly enhancing the electromagnetic field intensity within a narrow range in the nanocavity between the SHINs and the substrate38. The localized surface plasmon resonance (LSPR) of the sample can be derived from the dark-field scattering shown in Supplementary Fig. 2. A broad scattering peak ranges from 550 nm to 800 nm indicating SERS ability of the sample. This localized electric field enhancement effect has been proven to be widely applicable in various spectroscopic techniques, such as Raman spectroscopy, fluorescence, second harmonic generation, and sum frequency generation39–41.

Three-dimensional finite differential time-domain (3D-FDTD) simulation was conducted to calculate the electric field distribution surrounding SHINs and Au film under 640 nm circularly polarize electromagnetic wave excitation. Strong electromagnetic fields are observed in the nanocavity between Au SHINs and the Au substrate, and the Raman signals of the molecules located at these hotspots can be enhanced by more than seven orders of magnitude (Fig. 1f). The stimulated Raman spectra were conducted on an Au film adsorbed with MG molecules in the presence and absence of SHINs (Fig. 1g). It can be seen that SHINE-FSRS significantly amplifies the SRS signal, while no signals of MG are observed for normal SRS.

The SHINE-FSRS with different polarized Raman pump is present at Supplementary Fig. 3. The left circle polarized Raman pump can keep the enough Raman signal while the baseline aroused from the non-resonant signal is very small. Although the linear polarized Raman pump leads to larger Raman signal, the non-linear signal would also be larger. Thus, the Raman pump was set to left circle Raman pump. Meanwhile, the spectral intensity is proportional to the square of pump intensity (Supplementary Fig. 4). At the following experiments, the Raman pump power was optimized to ~200 nJ. Higher power would easily lead to sample damage and the lower power need a long time to obtained a quality spectrum.

The enhancement factor of SHINE-FSRS was quantitatively investigated using 4-nitrobenzenethiol (pNTP), phenyl isocyanide (PIC), and MG as probe molecules. The Raman intensity of each molecule varies with Raman pump wavelength (Fig. 2a–c). The trend of variation is consistent with the dark field scattering spectrum of SHINs (Fig. 2d, Supplementary Fig. 2), indicating the Raman enhancement originates from the plasmonic effect of SHINs. The maximum enhancement factor of SHINE-FSRS, obtained at 640 nm, when their corresponding wavelength falls around 710 nm, the SPR resonant wavelength. The result indicated that the enhancement is associated with radiational enhancement42,43. The enhancement factor (EF) is up to ~106, and the EFs of different molecules are on the same order of magnitude (Fig. 2e), indicating that EF is primarily driven by the electric field generated by the SHINs, with minimal interference from the electronic resonance (Supplementary Fig. 5)44.

Transient reflection spectroscopy revealing electronic dynamics of MG
In order to investigate the relaxation of the excited states of MG molecules, we used transient reflection spectroscopy to test MG adsorbed on an Au substrate (Supplementary Fig. 6). We select a 400 nm femtosecond pulse laser as the actinic pump, and a supercontinuum white light as the probe. The MG molecules are placed in the gap between SHINs and Au substrate (see detailed experimental procedure in the “Methods” section). The transient reflection spectral map of the sample contains three sets of transient characteristics, corresponding to molecules at different electronic energy states (Fig. 3a). We extracted three kinetic characteristic curves from the spectrum with a singular value decomposition algorithm (Fig. 3b), the broad absorption band at 550–720 nm can be attributed to ground state bleaching (GSB) of MG molecules according to the steady absorption spectroscopy (Supplementary Fig. 7). The fitting result indicates a rising time of about 0.3 ps and a relaxing time of about 1.95 ps. The transient signal at 760-880 nm corresponds to the S2 → S0 emission according to the steady emission spectroscopy (fluorescence spectroscopy, Supplementary Fig. 8). The kinetics at 760-880 nm can be fitted by a two-exponential function with time constants of 0.3 ps and 0.6 ps. The first-time constant originates from an internal conversion process from S2 → S1, while the second time constant originates from an internal conversion from S1 → S0 (Supplementary Fig. 9). As the S2 excited state emission band decays, the S1 excited state emission band gradually grows and decays with a time constant of 2 ps. Thus, we can reconstruct the process of MG molecules transferring between different electronic states after being excited by a 400 nm pulse. Under femtosecond pulse excitation at 3.1 eV, corresponding to the S0 → S2 energy gap (Supplementary table 2), the molecule is excited from S0 to the S2 state and relaxed to the S1 state, and then returns to the ground state (Fig. 3e).

SHINE-FSRS revealing structural changes of MG
To elucidate the evolution of the molecular structure of MG molecules during excited state relaxation, time-resolved in-situ SHINE-FSRS has been employed to monitor the reaction. We employed the narrow Raman pump at 640 nm and the broadband (400–800 nm) supercontinuum white light to obtain stimulated Raman signals. The femtosecond stimulated Raman spectra of the samples under a 400 nm actinic pump (Fig. 3c) were presented as the difference between the spectra with and without the actinic pump pulse. The main bands were the in-plane ring deformation + C–H in-plane bending (αring + βH) at 1250 cm–1, and the N–ph–C skeleton asymmetric and symmetric stretching at 1400 cm–1 and 1440 cm–1, respectively. Detailed Raman band assignments are given based on DFT calculation and listed (Supplementary table 1).

The kinetics of the photo-induced MG reaction can be obtained based on the evolution of the intensities of the characteristic Raman bands. Figure 3d displays the normalized intensity of the three Raman peaks (1250 cm−1, 1400 cm−1, and 1440 cm−1) as a function of the delay time between the 400 nm actinic pump pulse and the SHINE-FSRS signal acquisition. It can be seen that the kinetic curves of these three Raman peaks show an exponential decay with different lifetimes and are in one-to-one correspondence with transient reflection results (Supplementary table 3). The relaxation time of the Raman band at 1400 cm–1 (2.0 ps) matches the timescale of GSB in transient reflection spectra (2.4 ps), indicating that the molecular skeleton of MG molecules undergoes deformation after excitation. The Raman band at 1440 cm–1 shares the same time constant with S2 excited state emission. Thus, it can be assigned to N–ph–C skeleton symmetric stretching mode of MG at S2 excited state. The Raman band at 1250 cm–1 can be assigned to αring + βH of MG at S1 state. There by, we successfully observed the evolution of the molecular structure of excited MG molecules using SHINE-FSRS. The distinct kinetics of different vibrational modes, along with their one-to-one correspondence with the dynamics observed in transient reflection spectra, indicate that electronic excitation initiates subsequent geometric restructuring. According to these findings, we therefore hypothesize that the observed dynamics originate from intramolecular twisting triggered by the altered electronic distribution in the excited state.

To verify this hypothesis, we performed density function theory (DFT) to calculate the Raman cross-section of molecules at different torsion angles. The configurations of MG at different electronic states with minimum energy are calculated and shown in Fig. 3e. We calculated the Raman spectra of the molecule in the saddle point configuration of the potential energy surface, and extracted three vibrational modes with Raman shifts of 1255 cm–1, 1400 cm–1, and 1440 cm–1 from the results. It can be seen that the Raman cross-section of vibrational modes with Raman shifts of 1255 cm–1 and 1400 cm–1 increase with increasing torsion angle, while the 1440 cm–1 mode decrease. These results verify our hypothesis that intramolecular torsion occurs in MG after excitation (Supplementary Fig. 10b)45.

Plasma-induced resonance energy transfer produced by Ag SHINs
Plasmon-induced resonance energy transfer between plasmonic materials and molecules has been proven to be a promising pathway to accelerate excited state relaxing38,46. The results in Fig. 3 was obtained using Au SHINs as the Raman amplifiers. As the LSPR band of Au nanoparticles is located at >500 nm, the 400 nm pump cannot excite the LSPR effect of Au. Compared with Au, the plasmonic band of Ag nanoparticles is located at a shorter wavelength range. Therefore, Ag SHINs may generate stronger plasmonic electromagnetic fields under the 400 nm pump, thus accelerating the photo-induced reaction of MG.

To reveal the role of plasmonic effect in the photo-induced reaction of MG, we further investigated the ultrafast reaction dynamics by putting MG molecules in the nanocavity between Ag SHINs and Ag substrate using SHINE-FSRS (Fig. 4a). We observed similar Raman features as those obtained when using Au SHINs. However, compared with Au SHINs, the excited state signal lifetime of MG molecules is much shorter for Ag SHINs. We extracted the kinetic curves of the Raman peak located at 1400 cm–1 of two types of SHINs, and plotted them in the same diagram.

Detailed kinetic fittings of MG within Ag SHINs are shown in Fig. 4b. In the presence of Ag SHINs, the excited state signal of MG molecules undergoes a ~1 ps relaxation, which is much faster than that for Au SHINs (~5 ps) (Fig. 4b). Meanwhile, unlike Au SHINs, three characteristic Raman features decay with almost the same time constant. This indicates that Ag SHINs alter the excited state relaxation pathways of MG. We compared the transient reflection spectra of the MG on quartz and Au/Ag SHINs (see Supplementary Fig. 11). The kinetic features of MG on quartz and within Au SHINs show no apparent difference, indicating that Au SHINs does not significantly affect the molecular excited state dynamics. However, we did not observe any MG transient signal within Ag SHINs. This is probably because the opto-induced strong coherent acoustic vibrations conceal any transient signal generated by MG. Therefore, we can only investigate this phenomenon from the perspective of the influence of the localized plasmonic field on the emission of molecular excited states.

Previous works have reported that photonic environment can modify the emission rate of the emitters, known as the Purcell effect47,48. The Purcell effect consists two parts: enhanced excitation and enhanced emission rate. We performed 3D-FDTD to simulate the electromagnetic field distribution under 400 nm excitation (Fig. 4c) and emission rate enhancement of MG molecules within Au and Ag SHINs (Fig. 4d)49,50. In brief, the emission rate of MG γemi in the presence of Au/Ag SHINs by the excitation rate γexc and the quantum efficiency (QE):

γemi = γexc * QE (1)

where, γexc can be estimated as the square of the plasmonic field. The plasmonic field generated at the gap between Ag SHINs and Ag substrate is much stronger than that between Au SHINs and Au substrate (Fig. 4c). The averaged E/E0 values in the nano-gap from Fig. 4c were taken to estimate γexc, which is 1.4 for Au SHINs and 10.2 for Ag SHINs. The QE is the ratio between the decay rate due to radiative transitions and the total decay rate, which is a function of the emission wavelength. The results are plotted in Fig. 4d. For Au SHINs, the emission rate enhancement is close to 1, as MG’s S2 → S0 emission processes do not overlap with Au SHINs’ SPR band (Supplementary Fig. 2). The kinetics of MG in ethanol show no obvious difference compared to MG with Au SHINs further confirmed the weak interactions between the MG molecules and Au SHINs (Supplementary Fig. 12)51. For Ag SHINs, the emission rate enhancements for S2 → S0 and S1 → S0 are ~8-fold and 10-fold, respectively, due to their SPR band aligning with MG’s emission bands (Supplementary Fig. 2). These findings are consistent with ultrafast Raman results. The fluorescence intensity of Ag SHINs is ~10 times greater than that of Au SHINs at around 750 nm and ~5 times greater at around 560 nm, as evidenced by the enhanced fluorescence spectra (Supplementary Fig. 8) further confirm Ag SHINs’ enhancement of MG’s emission. These results proved the acceleration of the molecular dynamic caused by localized plasmonic field, providing direct experimental evidence for understanding fundamental mechanism of plasmon-molecules interactions and plasmon-enhanced photocatalysis.

In summary, we have established a SHINE-FSRS method that has ultrahigh sensitivity and temporal resolution. By putting molecules in the nanocavity between Au/Ag SHINs and Au/Ag substrates, the FSRS signals of surface species can be enhanced, thus allowing the in-situ monitoring of ultrafast surface reaction processes on the picosecond or even femtosecond timescale. The enhancement is strongly dependent on the matching degree between the Raman pump and the plasmonic band of SHINs, and a maximum enhancement factor of ~106 has been obtained. Using SHINE-FSRS, the ultrafast molecular dynamic process of the photo-induced reaction of MG molecules adsorbed on Au surfaces has been in-situ studied. Direct spectroscopic evidence, combining DFT simulations, demonstrates that MG would undergo intramolecular torsion with 1 ps under the excitation of a 400 nm pulse laser. Meanwhile, it is found that Ag SHINs can generate strong plasmonic fields under such excitation conditions. This can greatly accelerate the photo-induced reaction of MG, leading to the relaxation time decrease from ~5 ps to ~1 ps. The SHINE-FSRS method developed in this work can effectively study the structural evolution of surface species during reactions with ultrahigh temporal resolution, thus exhibiting great potential in the in-situ study of surface/interface catalytic processes.

Methods
Preparation of Au and Ag SHINs
Gold nanospheres were prepared according to the method of Frens. First, 1.4 mL of sodium citrate solution (1 wt.%) was added to 200 mL of boiling chloroauric acid solution (0.01 wt.%). The mixture was refluxed for 1 h and then cooled to room temperature to obtain 55-nm bare Au nanoparticles. A silica shell was coated on the bare Au nanoparticles35. First, 0.4 mL of (3-aminopropyl)trimethoxysilane solution (1 mM) was mixed with 30 mL of previously prepared bare Au nanoparticles solution. Next, 3 mL of sodium silicate solution (0.54 wt.%) was added, and the resulting mixture was placed in a water bath at 95 °C for 15 min. This resulted in the coating of a 2 nm silica shell. The Au@SiO2 SHINs were centrifuged at 5500 × g and washed twice with Milli-Q water.

Silver nanospheres were prepared as the following procedures. First, 10 mL of sodium citrate solution (1 wt.%) was added to 200 mL of boiling 1 mM AgNO3 solution (0.01 wt.%). The mixture was refluxed for 1 h and then cooled to room temperature to obtain 55-nm bare Ag nanoparticles. A silica shell was added to the bare Ag nanoparticles using the method mentioned above40.

Self-assembly of SHINs mono-layer film was prepared as follows. 10 μL 1 mM MG ethanol solution was dropped onto a quartz plate covered with a ~20 nm Au film. 10 mL SHINs solution was centrifuged at 5500 × g and washed with water three times. 3 mL cyclohexane and 5 mL 40 μM tetrabutyl-ammonium nitrate were then added into the concentrated solution. The solution was shaken and poured into a 10 mL beaker and stood to form two phases. A large and uniform monolayer of SHINs appeared at the interface between water and cyclohexane. The SHINs monolayer was then transferred onto the Au film.

The preparation of samples
Molecules (MG, PIC, pNTP) were adsorbed on Au/Ag films with self-assembled SHINs (Au or Ag cores, ~2 nm SiO2 shell). The substrate was prepared by depositing a ~20 nm Au/Ag film on glass, followed by adsorption of 10−6 M MG, pNTP, or PIC in ethanol for 1 hour, and deposition of SHINs. Measurements were conducted in air at 25 °C.

FSRS Setup and Experimental protocol of SHINE-FSRS
We designed and built the experimental setup (Supplementary Fig. 13). Briefly, a femtosecond Ti:Sapphire laser system provides fundamental output at 800 nm (100 fs, 1 kHz) (Legend Elite-Duo-FS, Coherent). Part of the 800 nm output is used to pump a BBO to create the pump pulse at 400 nm (100 fs, 1 kHz). Another part of the 800 nm output is used to pump visible optical parametric amplifier (OPA) (Topas 400-WL, Light conversion) after second harmonic bandwidth compressor (SHBC) to create the tunable picosecond Raman pump. The pulse duration is about 2.5 ps with in the tuning range from 470 to 900 nm (with SHG 300–900 nm), and the linewidth is ∼7 cm–1. A supercontinuum white light generated by focusing a small portion of the fs 800 nm output into a 2 mm thick sapphire window is used as the Raman probe. The white light spectrum covers from 420 nm to 800 nm. In the SHINE-FSRS setup, the picosecond Raman pump (2.5 ps, 640 nm) and the femtosecond Raman probe (broadband, 420–800 nm) are temporally overlapped to optimize the stimulated Raman signal, with the delay between the 400 nm actinic pump and the Raman pump-probe pair varied to capture the ultrafast dynamics.

To obtain SHINE-FSRS signals of the MG molecule, we assembled the molecules on the Au film, then transferred the SHINs monolayer on them. Due to its strong enhancement ability, only trace amounts of molecules are needed to generate significant Raman signals. In order to figure out the best working condition of our home-built SHINE-FSRS37, we use 4-nitrophenylthiophenol (pNPT) as a Raman probe to identify the enhancement of our equipment. pNPT molecules are chemically adsorbed on ~20 nm Au film plated on a 1 × 1 cm2 Quartz sheet. A mono-layer Au SHINs is assembled onto the Quartz sheet. The SHINE-FSRS setup used a 400 nm actinic pump (100 fs, 70 nJ), a 640 nm Raman pump (2.5 ps, ~200 nJ), and a 420–800 nm Raman probe (300 fs, 20 nJ), with pulse energies optimized to avoid artifacts. Meanwhile, to prevent sample damage from excessively high pulse energy and to place more probe molecules within our detection field, we employ a defocused detection method, which moderately enhances the signal intensity. Notably, the molecules absorbed in the gap between the SHINs and the Au film experience a significant enhancement in Raman intensity, reaching up to ~107 times, owing to the strong near-field coupling between the localized surface plasmons (LSPs) of the SHINs and the surface plasmon polaritons (SPPs) of the gold film. The wavelength-dependent correlations between extinction spectra and SHINE-FSRS enhancement factors (EFs) were investigated. The ensemble-averaged enhancement factor is estimated to be in the range of 106–107 with the Raman pulse at 640 nm.

DFT calculations and optical simulations
The DFT calculations were performed using the Gaussian 16 program suite (Supplementary table 1)52. The geometric structures optimization of malachite green molecules at different electronic states were carried out at the B3LYP/6-31G* theoretical level. The Raman spectra of the molecule at each configuration were then calculated (Supplementary Fig. 10a).

The electromagnetic field distribution of Au/Ag SHINs dimer on the Au/Ag film surface under a 400 nm wavelength plane electromagnetic wave was calculated using commercially available Lumerical 3D-FDTD Solutions software. The diameter of the original Au/Ag NPs in the simulation was set as 55 nm. The thickness of the silica shell was set as 2 nm. The refined structure was 0.3 × 0.3 × 0.3 nm3. The dielectric function of Au, Ag and silica was chosen from the material library of the software.

Data availability
The data generated or analysed during this study are included in this published article and its Supplementary information files. Source data are provided with this paper.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This paper describes the plasmon enhanced FSRS spectra of MG following an actinic pump pulse. The SHINE structure\ncorresponding to a Au/Ag nanosphere covered by a thin (2 nm) silica layer on a Au/Ag flat surface provides the plasmonic\nstructure that enhances the electric fields molecules in the hot spot region experience. Aside from the enhanced sensitivity\nprovided by the plasmonic fields, evidence for the structural rearrangement dynamics are extracted for the MG system.\nAdditionally results on Au and Ag nanocavities are compared.\nI have a number of concerns, some major and some minor, about the current submission:\n1. The discussion in the Introduction section is frankly inaccurate and missing important previous examples of PE-FSRS\nwhich SHINE-FSRS is an example. For example, the authors cite “conventional spectroscopic methods can only capture the\nsteady state results…”. In 2025 what does conventional mean? At this point aren’t pump probe studies with ultrafast sources\n“conventional”? Such techniques at least capture ultrafast electronic dynamics for more than 30 years. Are the authors trying\nto make the point that studying the ultrafast dynamics of nuclear dynamics is challenging for short-lived electronic states?\nThe authors cite Refs. 16, 17 as suggesting that FSRS somehow beats the uncertainty limit. Of course that is not true when\nproperly interpreted and furthermore these refs have nothing to do with FSRS. They are “conventional” impulsive OHD-\npump-probe studies.\nFurthermore, plasmonically enhanced FSRS has been previously demonstrated by the Van Duyne group in 2011 (Ref. 36)\nand in several other publications from this group. Enhancement factors ~106, similar to those reported here, were observed.\nThese relevant pioneering studies should be cited in the introduction.\n2. The abstract and introduction cites an enhancement factor (5.1 x 106) but no indication what molecular system this relates\nto. This is for what molecular system?\n3. In the methodology section the authors cite “integrating RIKE into the detection path” and cite Refs. 31-35. RIKE\nconfigurations (Refs. 16, 17) have to do generally with phase controlled local oscillator fields to read out the Re or Im part of\nthe optical response so not clear what the authors mean here and references 31-35 do not mention RIKES. Maybe the\nauthors are just implying polarization discrimination but a ¼ wave plate is evident in Fig. 1c. thus clarification with correct\nrelevant references is needed here.\n4. P. 6 lines 145 – 150. I presume SRS should be FSRS and MB should be MG. Ref 39 is an SFG paper so what relevance is that to a plasmonically enhanced (PE) FSRS measurement?\n5. PE-FSRS spectra are notorious for complicated line shapes often displaying dispersive character (e.g. Ref. 36) due to the\nrelative contributions of the Re and Im parts of the Raman vibrational line shape function to these spectra. Such line shapes\nare evident in Figs. 2c and 3a. Is this taken into account when the SHINE-FSRS signal are analyzed for use in the kinetics\nanalysis?\n6. MG has an electronic resonance, mentioned in passing, that appears coincident with the SPR of the Au system. This point\nshould be further emphasized since that electronic resonance attribute makes the study of these dynamics more accessible\npresumably. How does the SHINE-FSRS signal magnitude compare for MG (electronic resonance) and pNTP\n(electronically non-resonant)? What is the EF (enhancement factor) for MG on both Ag and Au substrates relative to that for\npNTP?\n7. Pump has two meanings in this paper: the actinic pump which moves population to the excited electronic state and the\nRaman pump which contributes to the Raman resonance on either the ground or excited electronic state. The authors\nshould make this distinction clear when a “pump” pulse is indicated in the text.\n8. P. 8 line 195-196 is not a sentence. Please fix this.\n9. P. 9 line 204. “…as a function of reaction time.” Reaction time is not an experimental variable here. Isn’t it clearer to say as\na function of delay between the actinic pump pulse and the SHINE-FSRS signal acquisition time? BTW, although not\nstated here I presume there was not delay between the ps Raman pump and fs Raman probe pulses. This should be explicitly\nstated.\n10. P. 9 line 215. Why can it be “anticipated” that intramolecular twisting occurs from just the FRSR intensity dynamics\nshown here? What additional observations would justify this interpretation?\n11. P. 9 lines 222-224 An argument is presented about A symmetry bands weakening and B symmetry bands increasing in\nintensity which is not explained. Both A and B vibrational bands are Raman allowed in C2 symmetry. Please explain the\nphysical basis for this point.\n12. P. 10 line233-234. Again a partial sentence that doesn’t make sense is given: “…the MG molecular occurs…”. Could it\nbe “intermolecular torsion occurs after the excitation”?\n13. Why is Fig. 3c plotted as I2 or |E/Eo|4? Isn’t 400 nm the actinic pulse? Thus a comparison at the E or I (|E|2) level seems\nrelevant not at the Raman level.\n14. Energy transfer is known to be responsible for so-called fluorescence quenching for electronically resonant systems\nwhen the radiation is also plasmonically resonant. Shouldn’t the observed dynamics also capture this ET effect?\nFurthermore, won’t these dynamics also contribute to Au and Ag SHINE-FSRS differences?\n15. Why should the “reaction dynamics” be faster on Ag than on Au if the alleged local plasmonic field is stronger? This point\nis not explained.\n16. What is the temporal duration of the spectrally broad Raman probe pulse?\nI think this manuscript is publishable after a major revision once the points above are adequately addressed.", "reviewer_2": "This study introduces an innovative method, SHINE-FSRS, which combines the use of so-called SHINERS—plasmonic\nnanoparticles coated with a thin glass layer—as active plasmonic enhancers for Femtosecond Stimulated Raman Scattering\n(FSRS), together with the integration of the Raman-induced Kerr effect (RIKE) into the detection path of the Raman\nscattering signal. This combination enabled both a substantial enhancement of the stimulated Raman signal by\napproximately six orders of magnitude and effective FSRS background suppression, allowing for the detection of weak\nRaman signals and significantly improving the signal-to-noise ratio (SNR). These innovations allowed the authors to\ndemonstrate applications in studies of ultrafast interfacial molecular dynamics with high sensitivity. The combined innovative\napproach brings Raman spectroscopic techniques closer to further development for investigating ultrafast processes,\nincluding those occurring on catalytic surfaces. Although a somewhat different approach involving aggregated plasmonic\nnanoparticles coated with a thick silica layer and detection of the SRS signal in the time domain—known as Impulsive\nStimulated Raman Scattering (ISRS)—was previously proposed by Pardeep Kumar et al. [1] for studying ultrafast molecular\nprocesses, and they achieved comparable signal enhancement factors (up to 10^6) [2], the approach proposed here differs\nsignificantly in its implementation. In some applications, it may offer substantial advantages and considerably greater\nversatility, especially for studies involving catalytic surfaces, where it is necessary to deliver the plasmonic enhancing\nmedium to the catalytically active area. This contrasts with previous works, where ultrafast process investigations seemed\nlimited to plasmonic surfaces encapsulated within a silica shell, thus restricting the accessibility of the active surface.\nIn my opinion, this report will be of interest to a broad audience, presents an innovative technique, and has the potential to\nsignificantly impact further research on ultrafast processes at interfaces. As such, it is worthy of publication. However, there\nare several points that may not be entirely clear and should be addressed before publication.\nMajor issues\nIn the report, the results and methodology were not sufficiently compared and discussed with reference to the existing\nliterature. Therefore, appropriate discussion and references should be included either in the introduction or within the\nrelevant discussions of the obtained results, as it is suggested in the following points.\n1. As already mentioned above, the approach proposed here is innovative; however, other successful applications of ISRS\ntechniques to ultrafast molecular processes have also been reported. The authors should highlight the advantages of their\napproach compared to these previously reported method: Hikaru Kuramochi and Tahei Tahara „Tracking Ultrafast Structural\nDynamics by Time-Domain Raman Spectroscopy” J. Am. Chem. Soc. 2021, 143, 26, 9699–9717\n2. The same team of researchers has also reported enhancement factors (EF) of the same order as those presented here:\nPardeep Kumar, Hikaru Kuramochi, Satoshi Takeuchi, Tahei Tahara „Time-Domain Observation of Surface-Enhanced\nCoherent Raman Scattering with 105–106 Enhancement” J. Phys. Chem. Lett. 2020, 11, 15, 6305–6311\n3. It appears that the experimental data provided in the manuscript are not sufficient to ensure the reproducibility of the\nresults. In particular, although the description and diagrams of the measurement setup are fairly detailed, there is a complete\nlack of information regarding the sample conditions, as well as the pulse energies or energy densities used to obtain the\npresented spectra. This information is of particular importance, since in these techniques both excessively low and\nexcessively high pulse energies can lead to artifacts, as was shown recently: Patryk Pyrcz and Sylwester Gawinkowski\n„Advancements in surface-enhanced femtosecond stimulated Raman spectroscopy: exploring factors influencing\ndetectability and shapes of spectra”. Nanophotonics, vol. 14, no. 1, 2025, pp. 1-12.\n4. Also, in the above-cited report by Pyrcz et al., a strongly dispersive Raman band structure was consistently observed\ndepending on various parameters. Such dispersive features have, in fact, been reported in all previous SE-FSRS studies,\nincluding several from the van Duyne group (e.g. Frontiera, R. R.; Henry, A.-I.; Gruenke, N. L.; Van Duyne, R. P. “Surface-\nEnhanced Femtosecond Stimulated Raman Spectroscopy” J. Phys. Chem. Lett. 2011, 2 (10),469, 1199–1203). It should be\nexplained why, in your recorded spectra, all Raman bands appear symmetric, as in conventional non-plasmonically\nenhanced FSRS spectra, while previous reports consistently show highly asymmetric, dispersive shapes. Is this due to your\ndifferent detection approach (RIKE) or differences in the sample? This point is particularly important, as these dispersive\nfeatures significantly hinder both the interpretation and practical applications of SE-FSRS. If your method indeed avoids this\nundesired phenomenon, it should be highlighted and, at the very least, explained which aspect of your experimental\napproach—distinct from previous reports—enables the elimination of such dispersion.\n5. In lines 150–158, you state that \"The Raman intensity is strongly dependent on the wavelength of the Raman pump, and\nthe Raman enhancement first increases then decreases with the increase of the wavelength of the Raman pump\n(Supplementary Fig. 4b).\" You also mention that the chosen excitation wavelength of 640 nm matches the\nplasmonic band. However, this may not be entirely accurate, as the indicated figure shows a very broad plasmon resonance, and it is\nmore likely that the observed profile reflects the resonant Raman enhancement profile of the analyte itself. This resonance can be\nshifted relative to the absorption band, especially when the analyte is deposited on gold nanoparticles. This effect has been\ndemonstrated, for example, in the resonance enhancement profiles for different Raman bands of malachite green, where the\nmaximum occurs at 640 nm, as shown in: Abdolvahab Amirsalari, Sepehr Razi, Sylwester Gawinkowski, „Multimodal\nmicroscope system for hyperspectral imaging of scattering directionality and Raman excitation spectroscopy\" J Raman\nSpectrosc 2023, 54(9), 97\nOn the other hand, in the following report using the FSRS technique, it was shown that the Raman excitation profile maxima\nmay also be located around 640 nm in solution:\nQiongyan Cen, Yuhan He, Mei Xu, Jingjing Wang, Zhaohui Wang „Wavelength dependent resonance Raman band intensity\nof broadband stimulated Raman spectroscopy of malachite green in ethanol” J. Chem. Phys. 015; 142 (11): 114201.\nhttps://doi.org/10.1063/1.4914188\n6. Similarly, excitation spectra for SERS have also been reported for the compound used to determine the enhancement\nfactor: Sabrina Juergensen, Patryk Kusch, Stephanie Reich „Resonant Raman Scattering of 4-Nitrothiophenol” Phys. Status\nSolidi B", "reviewer_3": "The manuscript describes the development of shell-isolated nanoparticle-enhanced femtosecond stimulated Raman\nspectroscopy (SHINE-FSRS) to probe ultrafast molecular dynamics of malachite green (MG) adsorbed on Au/Ag surfaces.\nWhile the integration of SHINERS with FSRS is an interesting approach, significant concerns remain regarding the novelty,\nclarity of explanations, technical accuracy, and experimental rigor. While the integration of SHINE with FSRS has potential,\nthe manuscript in its current form is unsuitable for publication in NC.\nBelow are detailed comments supporting the rejection decision:\n1. The authors claim innovation in combining SHINE with FSRS, but this approach does not sufficiently advance beyond\nprior studies. For instance:\n• Surface-enhanced FSRS (SE-FSRS) using gold nanoparticles has been extensively reported (e.g.", "reviewer_doi": "10.1021/ja503541v). The authors do not justify how their implementation\nsurpasses these precedents.\n2. The observation of distinct relaxation times for MG on Au versus Ag SHINs is highlighted as a key finding. However, the\nauthors provide only superficial speculation about plasmonic field effects without rigorous analysis:\n• While 3D-FDTD simulations (Fig. 3c) show stronger electromagnetic fields for Ag SHINs at 400 nm, no quantitative\ncorrelation is established between field intensity and the observed kinetic acceleration. For example, how does the\ncalculated field enhancement (Fig. 3c) translate to the difference in relaxation rates?\n3. Inconsistent References and Mislabeled Figures\n• Line 109: References 31–35 incorrectly cite prior work unrelated to the Raman-induced Kerr effect (RIKE). This section\nshould reference Ref. 36 instead.\n• Supplementary Figures: Critical data are either missing or mislabeled. For example, Supplementary Fig. 4d and\nSupplementary Fig 10 are not cited in the main text.\n• Line 345: “configuration were then calculated (Supplementary Fig. 4)” should be Supplementary Fig. 6.\n4. Surface-Enhanced Ground-State Raman:\n• The 640 nm Raman pump overlaps with MG’s S₀→S₁ transition (Supplementary Fig. 5b), implying pre-resonance\nenhancement in ground state FSRS. However, the enhancement factor for MG under 640 nm excitation is not reported,\nunlike pNTP (~5.1 × 10⁶). Does the FSRS pre-resonance enhancement by 640 nm influence the enhancement factor for MG\nAu SHINE?\n5. Surface-Enhanced Transient Absorption:\n• Transient signals in Fig. 2a (700–900 nm) likely arise from Au SHINE intrinsic plasmonic dynamics (DOI: 10.1038/s41598-\n018-28909-6). Control experiments comparing bare Au SHINs, MG/Au SHINs, and free MG are missing.\n• Similarly, Ag SHINE transient absorption data (with/without MG) should be provided.\n• The kinetic analysis of MG’s transient absorption is unclear. The assignment of 0.6 ps to S₁→S₀ internal conversion and 2\nps to S₁ emission contradicts the energy diagram in Fig. 2e. Global fitting of the transient datasets is strongly recommended\nto resolve ambiguities.\n6. Excited-State SHINE-FSRS Analysis\n• The divergent kinetics of the 1250 cm⁻¹, 1400 cm⁻¹, and 1440 cm⁻¹ modes (Fig. 2d) are unusual for FSRS studies. A\nmechanistic explanation linking these modes to specific structural changes is missing.\n• Supplementary Fig. 7: DFT calculations predict a negative Raman cross-section trend for the 1400 cm⁻¹ mode with\nincreasing torsion angle, directly conflicting with experimental observations (positive intensity changes). This discrepancy\ninvalidates the proposed torsional mechanism.\n• The manuscript fails to clarify why Ag SHINs induce uniform acceleration across all vibrational modes (Fig. 3b), whereas\nAu SHINs show mode-specific dynamics. This raises questions about whether plasmonic enhancement or chemical\ninteractions (e.g., charge transfer) dominate the observed effects. If plasmonic enhancements fundamentally alter the\nreaction pathway, the method cannot achieve its stated goal of in-situ monitoring the MG's reaction dynamics.", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Response to Reviewer #1\nThis paper describes the plasmon enhanced FSRS spectra of MG following an\nactinic pump pulse. The SHINE structure corresponding to an Au/Ag nanosphere\ncovered by a thin (2 nm) silica layer on an Au/Ag flat surface provides the plasmonic\nstructure that enhances the electric fields molecules in the hot spot region experience.\nAside from the enhanced sensitivity provided by the plasmonic fields, evidence for the\nstructural rearrangement dynamics is extracted for the MG system. Additionally results\non Au and Ag nanocavities are compared. I think this manuscript is publishable after a\nmajor revision once the points above are adequately addressed.\nResponse: We express our sincere gratitude to the reviewer for providing valuable\nsuggestions and comments. We greatly appreciate your constructive feedback and have\ncarefully addressed the issues you have raised, which greatly help us to improve the\nquality of the manuscript.\n1. The discussion in the Introduction section is frankly inaccurate and missing\nimportant previous examples of PE-FSRS which SHINE-FSRS is an example. For\nexample, the authors cite “conventional spectroscopic methods can only capture the\nsteady state results…”. In 2025 what does conventional mean? At this point aren’t pump\nprobe studies with ultrafast sources “conventional”? Such techniques at least capture\nultrafast electronic dynamics for more than 30 years. Are the authors trying to make the\npoint that studying the ultrafast dynamics of nuclear dynamics is challenging for short-\nlived electronic states?\nResponse: We greatly appreciate the reviewer for pointing out this imprecise\ndescription. The “conventional spectroscopic methods” in the Introduction section are\nmainly refer to normal Raman spectroscopy or IR that can provide fingerprint\ninformation of the probe species. According to your comments, we have revised the\ndescription on pages 3-4 of the maintext as follows:\n“Normal Raman spectroscopy or IR is a versatile tool to reveal the fingerprint\nstructures of steady species, but is often frustrated for the dynamic study. The transient\nabsorption (TA) spectroscopy can capture the electronic relative process with temporal\nresolution up to femtoseconds, but capturing the vibrational dynamics of short-lived\nintermediates during surface reactions remains challenging due to limitations in\nsensitivity and temporal resolution of many vibrational spectroscopic methods.”\nThe authors cite Refs. 16, 17 as suggesting that FSRS somehow beats the\nuncertainty limit. Of course, that is not true when properly interpreted and furthermore\nthese refs have nothing to do with FSRS. They are “conventional” impulsive OHD-\npump-probe studies.\nResponse: We greatly appreciate the reviewer for the comments. In conventional\ntime-resolved Raman spectroscopy, the fundamental resolution limit is dictated by the\ntime-bandwidth-product of 15 ps cm-1. Thus, there is a trade-off between temporal and\nspectral resolution. The uncertainty limit prevents achieving both high temporal\nresolution and high spectral resolution simultaneously. In FSRS, the experimental\nparameters that determine the temporal and spectral resolution are not a conjugate pair\nof variables. While the spectral resolution of FSRS is essentially limited by the\ndephasing time of the free-induction decay and the bandwidth of the Raman pump pulse,\nthe effective time resolution is determined by the cross-correlation width of the Raman\nprobe and the actinic excitation pulse. The key point here is that the high temporal\nresolution of FSRS is achieved with many measurements. According to the reviewer’s\ncomments, we have revised the description on page 4 of the maintext to avoid\nunnecessary misunderstandings as follows:\n“Femtosecond stimulated Raman spectroscopy (FSRS) has emerged as a powerful\nvibrational spectroscopy. In FSRS, the temporal overlap between Raman pump and\nprobe pulses (typically, a femtosecond white light continuum (WLC)) creates the\npopulation at the vibrational excited state and slices the target dynamics with\nfemtosecond temporal resolution firstly. Then the picosecond Raman pump reads out\nthe vibration population at the following process and provides a high-frequency\nresolution. Thus, high temporal and frequency resolution can be achieved\nsimultaneously with the measurement at different delays.”\nRegarding references 16 and 17, which describe optical Kerr-effect studies, have\nbe replaced with more relevant FSRS citations:\nMcCamant, D. W., Kukura, P., Yoon, S. & Mathies, R. A. Femtosecond broadband\nstimulated Raman spectroscopy: Apparatus and methods. Review of Scientific\nInstruments 75, 4971–4980 (2004).\nKukura, P., McCamant, D. W. & Mathies, R. A. Femtosecond Stimulated Raman\nSpectroscopy. Annu. Rev. Phys. Chem. 58, 461–488 (2007).\nFurthermore, plasmonically enhanced FSRS has been previously demonstrated by\nthe Van Duyne group in 2011 (Ref. 36) and in several other publications from this group.\nEnhancement factors ~106, similar to those reported here, were observed. These\nrelevant pioneering studies should be cited in the introduction.\nResponse: We sincerely apologize for not adequately citing the pioneering work\nby the Van Duyne group on PE-FSRS. Their study in 2011 and subsequent publications\ndemonstrated plasmon-enhanced FSRS with enhancement factors on the order of 106,\nwhich is highly relevant to our work. According to the reviewer’s suggestion, we have\ncited these references in the Introduction, acknowledging that our SHINE-FSRS builds\nupon these advancements by incorporating shell-isolated nanoparticles to further\nenhance sensitivity and applicability to surface reactions.\n2. The abstract and introduction cites an enhancement factor (5.1 x 106) but no\nindication what molecular system this relates to. This is for what molecular system?\nResponse: The enhancement factor of 5.1 × 106 was determined using p-\nnitrothiophenol (pNTP) as the probe molecule, as it avoids interference from resonance\neffects presented in malachite green (MG). According to the reviewer’s suggestion, we\nhave added this information in both the Abstract and Introduction section.\n3. In the methodology section the authors cite “integrating RIKE into the detection\npath” and cite Refs. 31-35. RIKE configurations (Refs. 16, 17) have to do generally\nwith phase controlled local oscillator fields to read out the Re or Im part of the optical\nresponse so not clear what the authors mean here and references 31-35 do not mention\nRIKES. Maybe the authors are just implying polarization discrimination but a ¼ wave\nplate is evident in Fig. 1c. thus clarification with correct relevant references is needed\nhere.\nResponse: We greatly appreciate the reviewer for the comments. There are many\ntypes of RIKES configurations. Our system is similar to the setup of Richard A. Mathies,\nFemtosecond Raman-induced Kerr effect spectroscopy (FRIKES) (J. Raman\nSpectroscopy, 2008, 39, 1526–1530). FRIKES used a broadband Raman probe pulse\nand a picosecond Raman pump pulse, and its spectrum is measured at frequency domain\ndirectly without heterodyne detection. The other typical configuration is OHD-RIKES,\nwhich used two femtosecond pulses and the signals interference with the Raman probe.\nThe frequency spectrum is obtained with Fourier Transfer.\nAt the Raman pump path, we added a polarizer, a half-wave plate, and a quarter-\nwave plate. At this configuration, the amplitude and phase difference of the horizontal\nand vertical components can be modulated. In our manuscript, the half-wave plate and\nthe quarter-wave plate were set to 0 and π/4, leading to the left-circle polarization. This\ncan significantly decrease the intensity of the Raman probe, and the signal can be\nimproved with longer time accumulation.\nIn our setup, it is possible to measure the real and imaginary part of the signal as\nyour proposed method, and we are trying this now. According to the reviewer’s\ncomments, we have revised page 5 as follows:\n“A polarizer, half-wave plate, and quarter-wave plate (fixed at 45°) in the Raman\npump path generate circularly polarized light, enabling crossed polarizers to suppress\n~99% of the probe background while preserving the Raman signal via the Kerr effect.\nThis configuration eliminates the white light interference, allowing extended\nintegration for detecting the weak interfacial signals.”\nRegarding refs. 31-35, they were used to provide more details about our laser\nsystem. According to the reviewer’s comments, we have moved them to a more proper\nposition and new Refs. has been added.\n4. P. 6 lines 145 – 150. I presume SRS should be FSRS and MB should be MG.\nRef 39 is an SFG paper so what relevance is that to a plasmonically enhanced (PE)\nFSRS measurement?\nResponse: We acknowledge the errors on Page 6, lines 145–150, where “SRS”\nshould be “FSRS” and “MB” should be “MG.” We have also checked the whole\nmanuscript to avoid such typographical and grammar errors. Meanwhile, we have also\nreplaced ref. 39 with a more appropriate reference:\nFrontiera, R. R., Henry, A.-I., Gruenke, N. L. & Van Duyne, R. P. Surface-\nEnhanced Femtosecond Stimulated Raman Spectroscopy. J. Phys. Chem. Lett. 2, 1199–\n1203 (2011).\n5. PE-FSRS spectra are notorious for complicated line shapes often displaying\ndispersive character (e.g. Ref. 36) due to the relative contributions of the Re and Im\nparts of the Raman vibrational line shape function to these spectra. Such line shapes are\nevident in Figs. 2c and 3a. Is this taken into account when the SHINE-FSRS signal are\nanalyzed for use in the kinetics analysis?\nResponse: We thank the reviewer for this insightful comment. The reviewer raises\nan important point about the complex line shapes in PE-FSRS spectra, which can\nexhibit dispersive character due to contributions from the real and imaginary parts of\nthe Raman vibrational line shape function.\nIn FSRS, the interference between the Raman probe, non-resonant signal and the\nFSRS signal leads to the dispersive line-shape especially when there is the electronic\nor plasmonic resonance.\nThe two polarizers in the Raman probe optical pass are set to be orthogonal. Thus,\nonly the vibrational bands are visible, and all the off-resonant spectral range will vanish.\nThe circle polarization of the Raman pump would make the non-resonant signal\nvanish. Therefore, there is no interference between the Raman probe, non-resonant and\nFSRS signals. The dispersive lineshapes in the time-dependent spectra in Fig.2c and 3a\nare induced by the pump pulse (these spectra are the difference between the spectra at\na certain delay time with and without the actinic pump pulse). In the spectra without\nthe pump pulse as marked as ‘ground’, there is no (at least not obvious) dispersive\nlineshape. Moreover, Figure R1 presents the original spectra of FSRS and there is no\ndispersive line-shape.\nAccording to the reviewer’s comments, we have added the above discussion on\npage 5 of the revised maintext and included Figure R1 in the revised Supplementary\nInformation (Supplementary Fig. 11).\nFig. R1. The raw SHINE-FSRS spectra of MG with Au SHINs.\n6. MG has an electronic resonance, mentioned in passing, that appears coincident\nwith the SPR of the Au system. This point should be further emphasized since that\nelectronic resonance attribute makes the study of these dynamics more accessible\npresumably. How does the SHINE-FSRS signal magnitude compare for MG (electronic\nresonance) and pNTP (electronically non-resonant)? What is the EF (enhancement\nfactor) for MG on both Ag and Au substrates relative to that for pNTP?\nResponse: We appreciate the reviewer’s constructive comment regarding the\npotential stimulated resonance Raman contributions to the SHINE-FRIKE spectra of\nmalachite green (MG). We added the FSRS of MG with different wavelength Raman\npumps in Fig. R2, which can explain this question more clearly.\nFig. R2 presents the SRS at different Raman pump wavelengths. The SRS spectra\nof MG in ethanol solution reach the maximum Raman intensity at 670 nm pumping. At\nthe surface without nanoparticles, the MG SRS is relatively weak as shown in Fig. 1g,\nwhile the SHINE-FSRS spectra of MG have much stronger signals with the maximum\nat 640 nm.\nAs for comparing the amplitude of the SHINE-FSRS signal to MG (electronic\nresonance) and pNTP (electronic non-resonance), under SHINE-FSRS conditions, the\nenhancement factor (EF) for p-nitrothiophenol (pNTP) on Au shell-isolated\nnanoparticles (Au SHINs) is ~5.1 × 10⁶. For MG with Au SHINs, the EF is ~8.2×106,\nThe enhancement factor of MG is slightly larger than that of pNTP, which is consistent\nwith our previous studies that MG in ethanol solution under 640 nm Raman excitation\nexhibits negligible resonance features. And with Ag shell-isolated nanoparticles (Ag\nSHINs), the EF is ~3.25×107, reflecting substrate-specific plasmonic enhancements.\nAccording to the reviewer’s comments, we have added the above discussion and Fig.\nR2 in the revised Supplementary Information.\nFig. R2. The FSRS of MG with different Raman pump wavelength. a, Raman gain\n(Stokes) of MG in an ethanol solution with different Raman pump wavelength. b,\nRaman loss (Anti-Stokes) of MG in an ethanol solution with different Raman pump\nwavelength. c, SHINE-FSRS spectra of MG with different Raman pump wavelength\nd, Raman intensity of MG with different Raman pump wavelengths.\n7. Pump has two meanings in this paper: the actinic pump which moves population\nto the excited electronic state and the Raman pump which contributes to the Raman\nresonance on either the ground or excited electronic state. The authors should make this\ndistinction clear when a “pump” pulse is indicated in the text.\nResponse: We acknowledge the potential for confusion due to the use of “pump”\nfor both the actinic pump (400 nm, exciting MG to the S2 state) and the Raman pump\n(640 nm, driving the Raman resonance). To avoid ambiguity, we have explicitly\ndistinguished these terms throughout the manuscript, using “actinic pump” for the 400\nnm pulse and “Raman pump” for the 640 nm pulse.\n8. P. 8 line 195-196 is not a sentence. Please fix this.\nResponse: The sentence has been revised to ensure grammatical correctness and\nclarity as follows:\n“The femtosecond stimulated Raman spectra of the samples under a 400 nm\nactinic pump (Fig. 3c) were presented as the difference between the spectra with and\nwithout the pump pulse”.\n9. P. 9 line 204. “…as a function of reaction time.” Reaction time is not an\nexperimental variable here. Isn’t it clearer to say as a function of delay between the\nactinic pump pulse and the SHINE-FSRS signal acquisition time? BTW, although not\nstated here I presume there was not delay between the ps Raman pump and fs Raman\nprobe pulses. This should be explicitly stated.\nResponse: We agree that “reaction time” is not an appropriate term, as it implies\na chemical reaction variable rather than the experimental pump-probe delay. We have\nrevised the statement to clarify that the kinetics are plotted as a function of the delay\nbetween the actinic pump pulse and the SHINE-FSRS signal acquisition time.\nMeanwhile, as the reviewer said, there was not delay between the picosecond\nRaman pump and the femtosecond Raman probe pulses. In our setup, the Raman pump\n(2.5 ps, 640 nm) and the Raman probe (broadband, 420–800 nm) are temporally\noverlapped to maximize the stimulated Raman signal, as described in the Methods\nsection and Supplementary Fig. 8.\n10. P. 9 line 215. Why can it be “anticipated” that intramolecular twisting occurs\nfrom just the FRSR intensity dynamics shown here? What additional observations\nwould justify this interpretation?\nResponse: We sincerely thank the reviewer for the comments. Below, we clarify\nthe basis for this anticipation and provide experimental and computational evidence, as\nwell as literatures, to strengthen this conclusion. We have modified the description in\nthe manuscript.\n(a) Experimental Evidence: SHINE-FSRS spectra (Fig. 3d) reveal divergent\nkinetics for MG’s Raman modes at 1250 cm⁻¹ (α + β , ~0.6 ps), 1400 cm⁻¹ (N–ph–\nring H\nC asymmetric stretching, ~2.0 ps), and 1440 cm⁻¹ (N–ph–C symmetric stretching, ~0.3\nps), correlating with transient reflection spectra (Fig. 3b, S2→S1: ~0.3 ps, S1→S0:\n~0.6 ps"}]

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