Excited Dye Molecules Research Articles

Visible-Light-Driven Hydrogen Release from Dye-Sensitized Hydrogen Boride Nanosheets.

Hydrogen boride (HB) nanosheets are expected to be safe and lightweight hydrogen carriers because of their high gravimetric hydrogen density (8.5 wt %) and photon-driven hydrogen release under mild conditions. However, previously reported HB nanosheets respond only to ultraviolet (UV) light to release hydrogen. In this study, we develop dye-modified HB nanosheets that can release hydrogen under visible light irradiation (>470 nm) without heat input. Hydrogen generation is initiated by electron injection from excited dye molecules into the conduction band of the HB nanosheets. The conduction band of the HB nanosheets is formed by the antibonding states of the B 2py and H 1s atomic orbitals, and the electrons injected from the dye molecules react with the protons of the HB nanosheets to release gaseous hydrogen molecules. Although the hydrogen production is terminated after long-term light irradiation owing to dye oxidation and/or loss of protons in HB nanosheets, the total amount of the released hydrogen molecules corresponds to approximately 25% of the protons in HB nanosheets even under the extra mild conditions. The addition of a sacrificial agent like iodine ions and a proton source like formic acid sustained the H2 generation from the dye-modified HB nanosheets under visible light irradiation for long term.

A near infra-red emitting supramolecular dye-polymer assembly as promising platform for protamine sensing

Detection and quantification of bioanalytes using near infra-red (NIR) probes provide several advantages, viz, negligible scattering of light, minimum interference from the background matrices, deep sample penetration, etc. Herein, we report a supramolecular dye-polymer complex, comprising of mono-cationic LDS-798 dye and multi-anionic polystyrene sulfonate (PSS), as a promising NIR emitting turn-on probe for protamine (Pr) sensing. The supramolecular complex displays moderate fluorescence enhancement for LDS-798 due to its binding onto PSS surface. Strikingly, in the presence of Pr, this complex displays further enhancement in its emission intensity, which is also substantiated by a significant increase in the excited-state lifetime of LDS-798 dye. This turn-on response is found to be highly selective towards Pr, which is attributed to the structural change taking place for the anionic PSS on its interaction with highly cationic Pr molecule. Such a conformational change creates several cavities into the modified PSS structure, which can suitably encapsulate LDS-798 dye via strong hydrophobic interaction. Accordingly, there is large decrease in the radiationless decay processes for the excited dye molecules, making them strongly emissive in nature. Furthermore, LDS-798−PSS complex is found to be quite robust against changing temperature and ionic strength of the medium, indicating its possible use as a fluorescent probe over a wide range of temperature and salinity.

A New Three-Component Photo-Initiating System for Visible Light Recording of Volume Holograms with Single-Pulsed Laser.

Versatile substituted electron-deficient trichloromethylarenes can easily be synthesized and combined with a Safranine O/triarylalkylborate salt to form a highly efficient three-component photo-initiation system that starts free radical polymerization to finally form holographic gratings with a single-pulsed laser. The mechanism of this photo-initiation most likely relies on an electron transfer from the borate salt into the semi-occupied HOMO of the excited dye molecule Safranine O, which after fragmentation generates an initiating alkyl radical and longer-lived dye radical species. This dye radical is most probably oxidized by the newly introduced trichloromethylarene derivative as an electron acceptor. The two generated radicals from one absorbed photon initiate the photopolymerization and form index gratings in a suitable holographic recording material. This process is purely photonic and does not require further non-photonic post treatments.

Efficient synthesis of a new heterogeneous gold nanocatalyst stabilized by di-alkyne ligand and its applications for photocatalytic dye degradation and transfer hydrogenation reaction

A new form of carbon-based ligand supported robust heterogeneous gold nanocatalyst was synthesized and its potential catalytic applications are demonstrated. The high yield (> 90%) synthesis procedure involves ligand exchange between hydrophilic polyvinylpyrrolidone polymer stabilized gold nanoparticles (Au:PVP) with a di-alkyne ligand (1,4-Diethynylbenzene). The ultrasmall stabilized gold nanoparticles (1.8 ± 0.3 nm) are bonded to di-alkyne ligand through acetylenic carbon atom (≡C-Au) with an electronically conjugated 3D network. The synthesized material (Au-P1) was meticulously characterized using several spectroscopic and microscopic techniques, e.g., Fourier transform infrared spectroscopy (FTIR), optical absorption spectroscopy (UV-Vis), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM) and thermogravimetric analysis (TGA). The Au nanocatalyst showed good photocatalytic activity for degradation of several organic dye molecules in aqueous phase under visible light irradiation in presence of oxidizing agent (H2O2). The proposed mechanism involves dye absorption on ligand surface through π-π interaction followed by transfer of electron from excited dye molecules to gold core through electronically conjugated ligand for generation of reactive oxygen species (·OH). The catalyst has also been demonstrated for transfer hydrogenation of organic carbonyl and nitro functional groups (>C=O, -NO2) with potassium formate (HCOOK) as hydrogen source in water. The catalyst could be recovered by simple filtration, and it was reused up to five cycles for both of these catalytic transformations with complete retention of its catalytic activity.

Fluorescence coupling to internal modes of 1D photonic crystals characterized by back focal plane imaging

The coupling of fluorescence with surface electromagnetic modes, such as surface plasmons on thin metal films or Bloch surface waves (BSWs) on truncated one-dimensional photonic crystals (1DPCs), are presently utilized for many fluorescence-based applications. In addition to the surface wave, 1DPCs also support other electromagnetic modes that are confined within the 1DPC structure. These internal modes (IMs) have not received much attention for fluorescence coupling due to lack of spatial overlap of their electric fields with the surface bound fluorophores. However, our recent studies have indicated that the fluorescence coupling with IMs occurs quite efficiently. This observed internal mode-coupled emission (IMCE) is (similar to BSW-coupled emission) indeed wavelength dependent, directional and S-polarized. In this paper, we have carried out back-focal plane imaging to reveal that the IMs of 1DPCs can couple with surface bound excited dye molecules, with or without a BSW mode presence. Depending on the emission wavelength, the coupling is observed with BSW and IMs or only IMs of the 1DPC structure. The experimental results are well matching with numerical simulations. The occurrence of IMCE regardless of the availability of BSWs removes the dependence on just the surface mode for obtaining coupled emission from 1DPCs. The observation of IMCE is expected to widen the scope of 1DPCs for surface-based fluorescence sensing and assays.

Coupling of silver nanoparticle-conjugated fluorescent dyes into optical fiber modes for enhanced signal-to-noise ratio

We present the optical coupling of the silver nanoparticles (AgNPs)-conjugated dye molecule into fiber optical modes for detecting fluorescence with the enhanced signal-to-noise (S/N) ratio. This near field coupling of the excited state of organic dye (FAM) molecules into the fiber multimodes occurs by immobilizing them on the exposed surface of fiber core, permitting the coupled light to be guided along the fiber for detection. This fiber based scheme is the first attempt to single out the fluorescence using fiber modes not for carrying excitation light but only for collecting emission light via the dye-fiber coupling. The emission-selective coupling into fiber modes turns out to be effective in reducing the unwanted background noise arising from both the false detection of excitation light and bulk autofluorescence.This scheme differs from the previously reported fluorescence sensors based on waveguides where guided modes at λex excite dye molecules via their evanescent fields. In addition, the local fields enhanced by AgNPs in close proximity to FAM molecules on the fiber core surface increase the rates of dye excitation and radiative decay/AgNP supported surface plasmon coupled emission. While focusing on demonstrating the proof-of-concept of the scheme presented, we obtain the maximum of 4.2-fold enhancement of the signal-to-noise (S/N) ratio in detecting fluorescence as compared to a conventional fluorescence detection scheme. The results presented in the fiber-based scheme may find an application where high S/N ratio fluorescence based biochemical assay is required in a small-sized device with remote sensing capability.

Combined Theoretical & Experimental Approaches for Molecular Design of NIR Dyes for Dye-Sensitized Solar Cells Aiming Towards Improved Efficiency and Stability

Introduction: Since its inception and first report in 1991, dye sensitized solar cells (DSSCs) have got great attentions towards the realization of lost cost solar energy harvesting owing to easy fabrication, lower raw materials and aesthetic beauty. In the recent past, DSSCs came in to the lime light owing to their potential applications for efficient room light harvesting due to very good performance under low light intensity and highly suitable for building integrated photovoltaics due to color tunability in combination of the controllable transparency. State-of-art DSSCs exhibiting power conversion efficiency (PCE) >13% in spite efficient photon harvesting only in the visible wavelength region give a good hope for the further enhancement in the PCE by development and implementation of novel potential dyes having sensitivity near-infrared (NIR) wavelength region utilizing the existing state-of-art DSSC fabrication technologies developed in last two decades. Apart from enhancing the PCE, increasing the stability is inevitable for the commercialization of DSSCs and nature of the anchoring group of the sensitizers are expected to play a vital role by controlling efficiency of charge injection and binding strength on the mesoporous wide band gap semiconductor like TiO2. A series squaraine dyes (SQ) having same p-conjugated mother core but varying anchoring group has been designed and subjected to QC calculations in both of the ground and excited states using Gaussian program. In parallel, some of the potential sensitizers have also been synthesized and subjected to photo-physical investigation aiming towards the verification of the theoretically predicted results. Experimental: In this work, a series unsymmetrical squaraine dyes (SQ) bearing different anchoring groups (SQ-138-SQ-156) as shown in the Fig. 1 were logically designed and subjected to QC calculations. In order to construct theoretical energy band diagram, HOMO energy level was calculated after structural optimization using 6-311G/DFT/B3PW91 and PCM model using Ethanol solvent. Optimized structures were then used for TD/DFT excited state absorption spectral calculations and wavelength associated with the full width at half maximum of the spectrum was considered to be Eg followed by calculation of energy of LUMO by the relation LUMO = HOMO + Eg. Some of the designed dyes bearing different anchoring groups were synthesized, characterized and subjected to photo-physical investigation including the DSSC fabrication and characterizations. Results and Discussion: A perusal of the Fig. 1, clearly corroborates that except two dyes that is SQ-141 and SQ-146 bearing hydroxyl and catechol anchoring groups, all of the designed dyes seems to suitable as sensitizers for the fabrication DSSCs using TiO2 as mesoporous electron accepting scaffold and I-/I3 – redox electrolyte. In parallel to theoretical QC calculations, some of the potential dyes were also synthesized and subjected to their photo-physical characterization before their utilization for DSSC fabrication. Photo-physical results for some of the experimentally synthesized dyes indicate that there was only a difference of about 60-70 nm (0.06 eV) in λmax and (±0.06 eV) in Eg between theoretical prediction and experiment results. At the same time, experimental energy band diagram for four of the synthesized dyes as shown in the inset of Fig. 1, exhibits excellent match with the theoretical results. Rate of dye adsorption and their binding strength on the mesoporous TiO2 for some of the synthesized dyes was also investigated. It has been found that dye with Phosphonic acid anchoring group although exhibit nearly rate of dye adsorption as compared to that of one bearing carboxylic acid anchoring group but depicted >60 times higher binding strength. On contrary, it exhibited drastically hampered PCE than that of dye bearing –COOH, which has been explained by poor electron injection from the excited dye molecule to the conduction band of TiO2 owing to highly diminished intramolecular charge transfer and electronic coupling with d-orbitals of the TiO2 as indicated by QC calculations. One of the newly synthesized dye SQ-140 bearing cyanoacrylic acid anchoring, exhibited not only very good photo-voltaic performance with PCE of about 6 % after simulated solar irradiation but also NIR photosensitization having photon harvesting mainly between the 500 nm-800 nm with peak of the incident photon to current conversion efficiency of nearly 80 % at 700 nm. Acknowledgement: SSP would like to express sincere thank JSPS to Japan Society for Promotion of Science for the financial support by Grant-in-Aid for scientific research (C) [Grant No.-18K05300] to carry out the research. Figure 1

Emission shift of an imidazole bridged diethylaminocoumarin and diphenyl

Diethylaminocoumarin with imidazole as the bridge unit and phenyl rings appended was synthesized by conventional condensing method and routinely characterized by nuclear magnetic resonance and high resolution mass spectra technology. The absorption and emission behavior were studied in various polar environment. It exhibit highly emissive character in methanol with 89% emission quantum yield. In solid state, the fluorescence color shifts to yellow part with emission peak around 563 nm. Emission decay in solid state demonstrates the single index character of the excited dye molecules. Together with the conformation derived from single crystal structure, balanced driving force between regular and irregular packing trend leads to the highly emissive character.

Effect of Mie resonance on photocatalytic hydrogen evolution over dye-sensitized hollow C-TiO2 nanoshells under visible light irradiation

Light utilization is one of the key factors for the improvement of photocatalytic performance. Herein, we design C-TiO2 hollow nanoshells with strong Mie resonance for enhanced photocatalytic hydrogen evolution in a dye-sensitized system under visible light irradiation (λ ≥ 420 nm). By tuning the inner diameters of hollow nanoshells, the Mie resonance in hollow nanoshells is adjusted for better excitation of dye molecules, which thus greatly enhances the light utilization in visible light region. This work shows the potential of Mie resonance in nanoshells can be an alternative strategy to increase the light utilization for photocatalysis.

Controlled two-mode emission from the interplay of driving and thermalization in a dye-filled photonic cavity

Two dimensional photon gases trapped in dye-filled microcavities can undergo thermalization and nearly ideal equilibrium Bose-Einstein condensation. However, they are inherently driven-dissipative systems that can exhibit an intricate interplay between the thermalizing influence of the environment given by the dye solution and the pump and loss processes driving the system out of equilibrium. We show that this interplay gives rise to a robust mechanism for two-mode emission, when the system is driven by an off-centered pump beam. Namely, after the system starts lasing in the dominantly pumped excited mode, in a second transition a photon condensate is formed in the ground mode, when the pump power is increased further. This effect is a consequence of the redistribution of excited dye molecules via the lasing mode in combination with thermalization. We propose to exploit this effect for engineering controlled two-mode emission and demonstrate that by tailoring the transverse potential landscape for the photons, the threshold pump power can be tuned by orders of magnitude.

Hydrogel Fluorescence Microsensor with Fluorescence Recovery for Prolonged Stable Temperature Measurements

This work describes a hydrogel fluorescence microsensor for prolonged stable temperature measurements. Temperature measurement using microsensors has the potential to provide information about cells, tissues, and the culture environment, with optical measurement using a fluorescent dye being a promising microsensing approach. However, it is challenging to achieve stable measurements over prolonged periods with conventional measurement methods based on the fluorescence intensity of fluorescent dye because the excited fluorescent dye molecules are bleached by the exposure to light. The decrease in fluorescence intensity induced by photobleaching causes measurement errors. In this work, a photobleaching compensation method based on the diffusion of fluorescent dye inside a hydrogel microsensor is proposed. The factors that influence compensation in the hydrogel microsensor system are the interval time between measurements, material, concentration of photo initiator, and the composition of the fluorescence microsensor. These factors were evaluated by comparing a polystyrene fluorescence microsensor and a hydrogel fluorescence microsensor, both with diameters of 20 µm. The hydrogel fluorescence microsensor made from 9% poly (ethylene glycol) diacrylate (PEGDA) 575 and 2% photo initiator showed excellent fluorescence intensity stability after exposure (standard deviation of difference from initial fluorescence after 100 measurement repetitions: within 1%). The effect of microsensor size on the stability of the fluorescence intensity was also evaluated. The hydrogel fluorescence microsensors, with sizes greater than the measurement area determined by the axial resolution of the confocal microscope, showed a small decrease in fluorescence intensity, within 3%, after 900 measurement repetitions. The temperature of deionized water in a microchamber was measured for 5400 s using both a thermopile and the hydrogel fluorescence microsensor. The results showed that the maximum error and standard deviation of error between these two sensors were 0.5 °C and 0.3 °C, respectively, confirming the effectiveness of the proposed method.

Optical imaging and spectroscopy of SnO2-rhodamine 6G composite's desiccation patterns

In this study, we produced self-assembly structures (desiccation patterns) in the drying sessile drops of SnO2-R6G colloidal suspension that have functional applications. Colloidal suspensions of SnO2 nanoparticles were synthesized using the sol-gel method and, subsequently, R6G molecules were added into the suspension. Centimeter-sized honeycomb- or tree-like self-assembled structures of the nanoparticle-dye composite are formed from the evaporating droplets on a flat glass surface. The usual “coffee ring” effect observed in the case of drying of a sessile drop of dye solution is inhibited this way, which is desirable in many applications. The structures were investigated using optical microscopy and spectroscopy. The resemblance between transmission and fluorescence images illustrates the feasibility of organizing dye molecules in a specific way using self-assembled nanoparticles as a template. However, dye fluorescence from the self-assembly is very weak, which might be due to photoinduced interfacial electron transfer from the excited dye molecules to the nanoparticles.

Investigation of Fluorescent Optical Properties of Fluorine-Boron Cored Dye

In this contribution, an F-B containing dye is readily synthesized. In chloro-carbon medium, it exhibit good solubility and stability. The emission peak value is determined to be 519 nm in chloroform. The highly emissive character is ascribed to the coordination lock, which inhibits the free rotation of methoxybenzene around the single bond. This BF2 locker inhibits the energy dissipation by thermal vibration to an extent and results strong fluorescence emission. In addition, electron deficiency feature of B atom also contributes to its strong emission character. Even though the π-conjugate system is small, the emission shifted significantly and the Stoke’s shift reaches to 170 nm. In addition, the film by doping into polycarbonate is also emissive. In solid state, the emission maximum reaches to 529 nm. Both in film and in solid, only slightly redshift are observed, demonstrating less interference of intermolecular interaction toward the excited dye molecules.

Kinetic Mechanism of Metal Enhanced Fluorescence by Gold Nanoparticle with Avidin–Biotin as Spacer and by Gold–Silver Core–Shell Nanoparticle Using Fluorescence Lifetime Image Microscopy

We study the effects of metal-enhanced fluorescence (MEF) on rhodamine B fluorophore by nanoparticles of varied shapes. The avidin–biotin system was used as spacer to connect the fluorophore to the surface of nanoparticles. Fluorescence lifetime image microscopy (FLIM) was used to detect emission lifetime for dye molecules on single nanoparticles. Spherical gold particles diameter of 60 and 170 nm, respectively, cube length of 70 nm, and rhombic dodecahedron (RD) diameter of 63 nm were used. In the measured emission curves of rhodamine B, we obtained a short component with lifetime 16–26 ps attributed to the fluorophore under influence of the local electric field of gold nanoparticle and energy dissipation to nanoparticle. The second lifetime is 200, 270, 280, and 330 ps for 170 nm sphere, 70 nm cube, 63 nm RD, and 60 nm sphere, respectively. This component is referred to as the bright mode of nanoparticle which is coupled to the excited dye molecule and transfers energy back to the fluorophore. On the ba...

Quantum Sensing of Motion in Colloids via Time‐Dependent Purcell Effect

AbstractLight–matter interaction dynamics is governed by the strength of local coupling constants, tailored by surrounding electromagnetic structures. Characteristic decay times in dipole‐allowed fluorescent transitions are much faster than mechanical conformational changes within an environment and, as a result, the latter can be assumed static during the emission process. However, slow‐decaying compounds can break this commonly accepted approximation and introduce new interaction regimes. Here, slow‐decaying phosphorescent compounds are proposed to perform quantum sensing of the nearby structure's motion via observation of collective velocity‐dependent lifetime distributions. In particular, characteristic decay of an excited dye molecule, being comparable with its passage time next to a resonant particle, is modified via time‐dependent Purcell enhancement, which leaves distinct signatures on properties of emitted light. Velocity mapping of uniformly moving particles within a fluid solution of phosphorescent dyes is demonstrated via the analysis of modified lifetime distributions. The proposed interaction regime enables performing studies of a wide range of phenomena, where time‐dependent light–matter interaction constants can be utilized for extraction of additional information about a process.

Water solvates slower than expected

Given how common water is, you’d think by now we would know just about everything there is to know about it. Not so. A new study shows that when it comes to orienting around a solute, water molecules are a lot more sluggish than generally thought (J. Chem. Phys. 2018, DOI: 10.1063/1.5034225). Years of spectroscopy experiments using lasers with short pulses, led researchers to consider water to be among the fastest-acting solvents, with a response time in the subpicosecond range. Those studies have generally been done by probing electronic properties of a water-dissolved solute, often an excited dye molecule. But rather than study water solvation from the solute’s point of view, Saima Ahmed, Peter Hamm, and coworkers at the University of Zurich used a fast terahertz (THz) vibrational spectroscopy method to carry out the experiment from water’s perspective. THz, or far-infrared, light uniquely probes collective motions of groups of water

Minimizing the charge recombination rate at the FTO/Zn2SnO4 interface by metal oxide semiconductors in DSSCs

Charge recombination at interfaces is one of the main factors that limit the power conversion efficiency of dye-sensitized solar cells. In this work, to reduce the charge recombination at the transparent conductive oxide/mesoporous Zn2SnO4 interface and then to improve the photovoltaic performance, different types of metal oxide semiconductor thin films (including SnO2, TiO2 and ZnO) are deposited on the FTO substrate by thermal evaporation method. The results reveal that in comparison with SnO2 and ZnO, the TiO2 dense layer acts as the most appropriate blocking layer for suppressing the charge recombination and increasing the short-circuit current density and power conversion efficiency of the fabricated device. Furthermore, because of the formation of energy barrier at the FTO/Zn2SnO4 interface, the charge recombination rate is minimized and the injected electrons from the excited dye molecules into the conduction band of Zn2SnO4 are accumulated in its conduction band which leads to upward shift of the Fermi level and increases open-circuit voltage. The maximum power conversion efficiency of 3.02% with short-circuit current density of 7.36 mA/cm2 and open-circuit voltage of 664 mV is obtained for the device comprising TiO2 blocking layer.

Probing of Reorganization Dynamics within the Different Phases of Themotropic Liquid Crystals

AbstractSolvent properties of two liquid crystalline solvents (LCs), 4‐n‐pentyl‐4/‐cyanobiphenyl (5CB) and 4‐n‐octyl‐4/‐cyanobiphenyl (8CB) are studied by exploiting their intrinsic fluorescence. Solvation dynamics of LCs in crystalline, liquid crystalline and liquid phases are observed by utilizing the dynamic Stokes shift in the time resolved emission spectrum (TRES) of an excited dye molecule coumarin 153 (C153) immersed within the LCs. With increasing temperature, transitions occur from crystalline to smectic/nematic and finally to liquid phase for these thermotropic LCs. At high temperature, liquid crystalline phases with substantial orientational orders are transformed to isotopic liquid phases. In this phase, peak positions of intrinsically fluorescent LCs are shifted towards the higher energy side with lowering its fluorescence quantum yields (φf) as compared to the emission peak positions and quantum yields of LCs in other anisotropic phases. Solvation dynamics study shows that the average solvation time of C153, immersed within the liquid phases of LCs, is about an order of magnitude faster as compared to that within a crystalline phase of the same substrate (5CB or 8CB). This observation is substantiating the fact that even within a complete crystalline phase a fluid like motion of the LC solvent molecules still exists. Average solvation time of C153 follows a descending order when we move from a complete crystalline phase to liquid crystalline phase to complete liquid phase.

SnO2/ZnO composite dye-sensitized solar cells with graphene-based counter electrodes

Abstract We have pioneered in developing dye-sensitized solar cells with interconnected nanoparticles of semiconductors other than TiO2 and we found that despite impressive properties of semiconducting materials such as ZnO and SnO2 which should theoretically give better performances than those based on TiO2, they give quite inferior performances and we explained this unprecedented fact by considering faster recombination of injected electrons in the latter semiconductor nanoparticles than those in TiO2 nanoparticles. To circumvent this problem, we introduced a novel technology in which we covered the surfaces of interconnected nanoparticles of SnO2 by an ultra-thin layer of a wide band-gap semiconductor or an insulator where the thickness of the layer is ∼1 nm or less such that electron injection from the excited dye molecules to the conduction band of the semiconductor nanoparticles is possible but injected electrons are incapable of penetrating the insulating barrier layer. In this way, we were able to suppress recombination significantly and such composite film based dye-sensitized solar cells gave efficiencies comparable to those based on TiO2 nanoparticles. We then realized that platinum used in dye-sensitized solar cell counter electrodes accounts for nearly 40% of the cost of these solar cells and hence limits their practical application. We then worked on alternative materials and found that carbon based counter electrodes can be tailored to give efficiencies closer to those of Pt counter electrode based solar cells. In extending this study we now worked on graphene as counter electrode material for composite SnO2/ZnO dye-sensitized solar cells. We report in this manuscript the optimizations of this low-cost counter electrode based dye-sensitized solar cell to give performance closer to those of expensive platinum based counterparts.

Active Tuning of Strong Coupling States between Dye Excitons and Localized Surface Plasmons via Electrochemical Potential Control

Here we report the tuning of a number of excited dye molecules that were strongly coupled with the localized surface plasmons (LSPs) of Au nanostructures by electrochemical potential control. Using the redox-state-tuned dye molecules and several types of metal nanostructures with distinct LSP energies, active control of the high coupling strength was achieved via an electrochemical potential-based control method. One interesting finding of the present work is that the parabolic behavior of the coupling strength in the range between 0.10 and 0.27 eV is dependent on the electrochemical potential; this has not been observed previously. Anticrossing plots showing the energies of the upper and lower states of the coupling to the LSP energy suggest that the number of dye molecules contained in the cavity-confined LSP field is controlled not only by the redox states of the dye molecules but also by the interactions between the dyes and the metal surfaces. The present finding provides a novel route to control lig...