J-aggregates Of Cyanine Dyes Research Articles

Nonlinear trimer resonators for compact ultra-fast switching

We propose and numerically verify a scheme for compact optical modulation which can enable complex directional switching of signals in integrated micro-optical circuits within hundreds of femtoseconds. The scheme is based on a trimer comprised of two identical silica whispering gallery mode (WGM) microresonators spaced by a central non-linear WGM resonator. The non-linear resonator is in the form of a silica cylinder with a thin coating of an ultrafast Kerr nonlinear material (a J-aggregate of cyanine dye). Using a two-dimensional finite-difference time-domain method and realistic material and structural parameters, we investigated the near-field coupling from a waveguide to the trimer and the subsequent switching process. In our scheme the sandwiched central control resonator has a resonant frequency that is mismatched to that of the input and output resonators. Therefore the optical energy is coupled from the waveguide into only the primary resonator in linear operation. However, for control light intensities of more than approximately 10(-2) W/microm the effective index and hence eigenfrequency of the central resonator can be shifted to match that of its neighbors and hence the optical energy can be redirected.

Uniform exciton fluorescence from individual molecular nanotubes immobilized on solid substrates

Self-assembled quasi one-dimensional nanostructures of pi-conjugated molecules may find a use in devices owing to their intriguing optoelectronic properties, which include sharp exciton transitions, strong circular dichroism, high exciton mobilities and photoconductivity. However, many applications require immobilization of these nanostructures on a solid substrate, which is a challenge to achieve without destroying their delicate supramolecular structure. Here, we use a drop-flow technique to immobilize double-walled tubular J-aggregates of amphiphilic cyanine dyes without affecting their morphological or optical properties. High-resolution images of the topography and exciton fluorescence of individual J-aggregates are obtained simultaneously with polarization-resolved near-field scanning optical microscopy. These images show remarkably uniform supramolecular structure, both along individual nanotubes and between nanotubes in an ensemble, demonstrating their potential for light harvesting and energy transport.

J-aggregation of cyanine dyes by self-assembly

The importance of highly ordered surfaces, containing adsorptive surface states, is discussed for J-aggregation by self-assembly. Such nucleating surfaces are nanometer-sized edges and corners of cubic AgBr microcrystals, or surface iodide-clusters located along edges and corners of AgBr:I microcrystals. Of particular interest are dendrimers, monoatomic steps on terraced silver halide microcrystals and fullerene derivatives as nucleating surfaces. Molecular organisation into J-aggregates by self-assembly was realized using aprotic, apolar solvents for fullerenes, and polar solvents for dendrimers and monoatomic surface steps. By using dendrimers as nucleating agents in mesopores of metal oxide nanoparticle coatings, size-controlled and stable J-aggregates with high optical densities and strong fluorescence were obtained reproducibly. Such films may be useful for sensors, opto-electronics, lighting and photovoltaics.

Synthesis and Spectroscopic Studies of Composite Gold Nanorods with a Double-Shell Structure Composed of Spacer and Cyanine Dye J-Aggregate Layers

The composite gold nanorods (Au NRs) having a double-shell structure composed of Au NR (core), spacer layer (inner shell), and J-aggregate (JA) layer (outer shell) have been synthesized to examine the spectroscopic properties of the hybrid system in which the localized surface plasmon is coupled with the molecular exciton of JA. The spacer layer consisting of N,N,N-trimethyl(11-mercaptoundecyl)ammonium chloride plays a significant role in the formation of JA shell for several kinds of cyanine dyes. The absorption spectra of composite NRs are characterized by a distinct dip near the J-band when the plasmon energy of Au core is close to the exciton energy of JA shell, whereas a normal J-band peak appears when two energies are widely different from each other. The gradual change from the dip type to peak type absorption was observed when the plasmon energy was modulated by varying the aspect ratio of Au NR. Furthermore, composite NRs with thicker spacer layers have been fabricated by inserting the multilayer shell of polyelectrolytes between TMA and JA layers. They exhibited an alteration of the spectral line shape from the dip type to peak type with increase in the thickness of spacer layer. These observations have been interpreted in terms of the strength of the exciton-plasmon coupling, which is sensitive to the configuration of composite NRs as well as the relative difference between plasmon and exciton energies.

Tuning of the Spectroscopic Properties of Composite Nanoparticles by the Insertion of a Spacer Layer: Effect of Exciton−Plasmon Coupling

Composite nanoparticles (NPs) having a double-shell structure, Au core, spacer layer (inner shell), and J-aggregate (JA) layer (outer shell) (Au/spacer/JA) have been synthesized. The spacer layer composed of N,N,N-trimethyl(11-mercaptoundecyl)ammonium chloride played an important role in promoting the J-aggregation of anionic cyanine dyes on the surface, as evidenced by the successful formation of the JA layers with four kinds of anionic cyanine dyes. It was found that the presence of a spacer layer causes a significant change in the line shape of the absorption spectrum, particularly near the J-band; there is the appearance of a peak type absorption for the composite NPs with the double-shell structure, while there is a dip type absorption for the ones without the spacer layer. The change from the peak type absorption to the dip type absorption in the Au/spacer/JA NPs occurs when the size of the Au core is varied from 5 to 15 nm. These observations would indicate that the strength of exciton-plasmon coupling between the Au core and the JA layer is enhanced with the increase in the core size or the decrease in the separation between the Au core and the JA shell. The photoluminescence arising from the JA can be detected for the composite NPs with the double-shell structure, showing that the quenching by the Au core is effectively suppressed by the spacer layer.

UV-vis Spectroscopy and Cyclic Voltammetry Investigations of Tubular J-Aggregates of Amphiphilic Cyanine Dyes

The redox and light absorption properties of immobilized aggregates of the cyanine dye 3,3'-bis(2-sulfopropyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimidacarbocyanine (C8S3) on transparent, conductive indium tin oxide (ITO) electrodes have been studied directly using cyclic voltammetry (CV) in conjunction with UV-vis spectroscopy to elucidate unique mechanistic features of J-aggregate oxidation. C8S3 self-assembles in aqueous solution to form double-walled, tubular J-aggregates with ~13 nm diameter and lengths up to several hundred nanometers. Spectroelectrochemical measurements indicate that irreversible J-aggregate oxidation occurs primarily along the outer wall of the tubular structure as evidenced by the potential-induced irreversible bleaching of J-band absorption. Additionally, J-aggregate oxidation involves both electrochemical and chemical steps in which dimerization and subsequent dehydrogenation of the J-aggregate leads to the formation of a new dehydrogenated dimer oxidation product.

Transfer of optically active polyelectrolyte multilayers by micro-contact printing

We describe the patterning of optically active material using the micro-contact printing technique. The optical active layer is an organized J-aggregated cyanine dye film, deposited onto a patterned PDMS stamp using a layer-by-layer technique, based on an alternate adsorption of oppositely charged species. The resulting polyelectrolyte multilayers (PEMs) are transferred by micro-contact printing onto bare Pyrex or silver-coated Pyrex substrates. AFM, SEM and optical images are presented, showing that the micrometer scale pattern is well transferred onto the substrate. The absorption spectra of the transferred active layer indicate that the particular optical properties of the transferred aggregated dye, which are crucial for polariton diodes or plasmonic devices, are not modified by the process. This work shows that micro-contact printing used in combination with the layer-by-layer deposition of PEMs (allowing molecular scale control of the layer thickness) has a specific potential for the fabrication of devices involving optical organic materials.

Ternary AOT/water/hexane systems as “micellar sieves” for cyanine dye J-aggregates

We investigate the behavior of J-aggregates of a cyanine dye, 3 , 3 ′ -di-( γ-sulfopropyl)- 4 , 5 , 4 ′ , 5 ′ -dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt, in AOT/water/hexane reverse micelles ( W = 2 – 50 ), both during the course of rapid microemulsion formation and then after stabilization of the microemulsions at thermodynamic equilibrium. We suggest a new mechanism for J-aggregate formation in reverse micelle solutions. According to this model J-aggregates are formed in the aqueous phase prior to formation of a stable microemulsion, rather than in the process of intermicellar exchange. Reverse micelles encapsulate only those J-aggregates whose size is smaller than the mean size of the water pool. Larger J-aggregates located in hexane gradually precipitate from solution. It is demonstrated that micellar solutions can be used as “sieves” for selection and stabilization of J-aggregates with a desired size.

Efficient fluorescence resonance energy transfer in highly stable liposomal nanohybrid cerasome

Highly stable and freestanding nanohybrid cerasome with non-covalently linked two J-aggregates of cyanine dyes was constructed as a model to advance conceptual understanding of excitation energy transfer and energy trapping in connection with photobiological processes.

Spectroelectrochemical Investigation of Double-walled Tubular J-aggregates of Amphiphilic Cyanine Dyes

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Anomalous Surfactant-Induced Enhancement of Luminescence Quantum Yield of Cyanine Dye J-Aggregates

Formation of the “J-aggregate-surfactant” complex for three cyanine dyes (L-21, LC-1 and PIC) in binary solutions containing cationic surfactant CPB at the concentration higher than the critical micelle concentration has been observed. The complex formation causes a significant increase of J-aggregate luminescence quantum yield and a decrease of radiative lifetime. The model of exciton self-trapping suppression in the “J-aggregate-surfactant” complex that causes changes of luminescence parameters has been proposed.

Particularities of surface plasmon–exciton strong coupling with large Rabi splitting

This paper presents some of the particularities of the strong coupling regime occurring between surface plasmon (SP) modes and excitons. Two different active materials were deposited on a silver film: a cyanine dye J-aggregate, and a two-dimensional layered perovskite-type semiconductor. The dispersion relations, which are deduced from angular resolved reflectometry spectra, present an anticrossing characteristic of the strong coupling regime. The wavevector is a good parameter to determine the Rabi splitting. Due to the large interaction energies (several hundreds of milli-electron-volts), the calculations at constant angle can induce an overestimation of the Rabi splitting of more than a factor of two. Another property of polaritons based on SP is their nonradiative character. In order to observe the polaritonic emission, it is thus necessary to use particular extraction setups, such as gratings or prisms. Otherwise only the incoherent emission can be detected, very similar to the bare exciton emission.

Spectroelectrochemical Investigation of Double-Walled Tubular J-Aggregates of Amphiphilic Cyanine Dyes

The amphiphilic cyanine dye 3,3‘-bis(2-sulfopropyl)-5,5‘,6,6‘-tetrachloro-1,1‘-dioctylbenzimidacarbocyanine (C8S3) self-assembles in aqueous solution to form double-walled, tubular J-aggregates with ∼13 nm diameters and lengths up to several hundred nanometers. The redox and light absorption properties of immobilized J-aggregates on transparent, conductive indium tin oxide (ITO) electrodes have been studied directly using cyclic voltammetry (CV) in conjunction with UV−vis spectroscopy to elucidate unique mechanistic features of J-aggregate oxidation. Morphological properties were examined using in situ atomic force microscopy (AFM). Irreversible J-aggregate oxidation appears to occur primarily along the outer wall of the tubular structure as evidenced by the potential-induced irreversible bleaching of J-band absorption. Voltammetric studies as a function of scan rate and pH indicate that J-aggregate oxidation involves both electrochemical and chemical steps in which dimerization and subsequent dehydrogena...

Excitons in molecular J-aggregates of cyanine dyes: Simulation of trapping and energy transfer

A theoretical model is provided to simulate the energy transfer and trapping of excitons in cyanine J-aggregates for various geometrical configurations. Intermolecular interactions are calculated using the extended dipole method. Frenkel exciton states are obtained by a numerical diagonalization of the aggregate Hamiltonian taking into account the static disorder. A model of exciton–phonon coupling is used to describe the trapping and the energy transfer processes among the exciton states. Scattering rates are calculated and used in a Master Equation to obtain the time evolution of the excitonic populations after initial excitation. Configurationally averaged absorption lineshapes and time-resolved fluorescence decays are obtained. Our simulation model is applied to describe the excitation energy transfer between two closely spaced linear chains of pseudoisocyanine (PIC) molecules and to a two-dimensional monolayer composed of a mixing of oxacyanine and thiacyanine molecules.

Highly efficient resonant coupling of optical excitations in hybrid organic/inorganic semiconductor nanostructures

The integration of organic and inorganic semiconductors on the nanoscale offers the possibility of developing new photonic devices that combine the best features of these two distinct classes of material. Such devices could, for example, benefit from the large oscillator strengths found in organic materials and the nonlinear optical properties of inorganic species. Here we describe a novel hybrid organic/inorganic nanocomposite in which alternating monolayers of J-aggregates of cyanine dye and crystalline semiconductor quantum dots are grown by a layer-by-layer self-assembly technique. We demonstrate near-field photon-mediated coupling of vastly dissimilar optical excitations in the two materials that can reach efficiencies of up to 98% at room temperature. By varying the size of the quantum dots and thus tuning their optical resonance for absorption and emission, we also show how the ability of J-aggregates to harvest light can be harnessed to increase the effective absorption cross section of the quantum dots by up to a factor of ten. Combining organic and inorganic semiconductors in this way could lead to novel nanoscale designs for light-emitting, photovoltaic and sensor applications.

Solid state cavity QED: Strong coupling in organic thin films

We review our research efforts to develop solid state integrated devices that operate in the strong coupling limit of cavity quantum electrodynamics (QED) for eventual application in high speed optical switching, optical computing, and quantum computing. Our devices contain J-aggregates of (organic) cyanine dyes which, by virtue of their molecular arrangement and strong dipolar coupling, exhibit a collective narrow linewidth high oscillator strength optical transition. Using J-aggregates, the strong coupling limit can be reached at room temperature with large coupling strengths (Rabi-splitting >250 meV) in exciton–polariton microcavity structures. We demonstrate that high quality nanoscale thick J-aggregate films can be uniformly deposited over macroscopic substrates, engineered at the molecular level, and patterned into single or multi-dimensional photonic bandgap structures. Our unique methods for depositing J-aggregates enabled us to structure light emitting devices that demonstrated the first ever electrically pumped polariton emission, uniquely accomplished in room temperature operation. Additionally, we demonstrated critically coupled resonators that concentrate nearly all of the incident light into 5 nm thick J-aggregate films, yielding a record high effective absorption constant of 6.8 · 10 6 cm � 1 for films with thickness that is less than 1% of the incident light wavelength. Such remarkable optical properties, enabled by scalable deposition techniques, suggest that J-aggregates are a unique materials platform on which to demonstrate integrated exciton–polariton devices with the far reaching properties of polaritons in the optical domain. � 2007 Elsevier B.V. All rights reserved. PACS: 71.36.+c; 71.35.Aa; 85.60.Jb; 78.40.Me

Single Particle Spectroscopic Investigation on the Interaction between Exciton Transition of Cyanine Dye J-Aggregates and Localized Surface Plasmon Polarization of Gold Nanoparticles

The interaction between molecular exciton and localized surface plasmon (LSP) polarization has been investigated by measuring light scattering spectra of single gold nanoparticles coated with cyanine dye J-aggregate. The spectral dip reflecting absorption spectral band of the J-aggregate varies with the particle size and the distance between the J-aggregates and the surface of gold nanoparticles. By comparing the experimental results with theoretical calculations based on the Mie theory, we demonstrate that the LSP polarization affects the peak and shape of the J-aggregate absorption band when the exciton resonance peak locates near the LSP resonance peak and when the separation of the J-aggregate from the metal surafce is short. The modification of the J-aggregate exciton band induced by LSP is considered to be due to strong coupling between the molecular exciton transition and the LSP resonance of metallic nanoparticles.

Formation and Behavior of J-aggregated Cyanine Dyes in Silver Halide Photographic Materials

Formation and Behavior of J-aggregated Cyanine Dyes in Silver Halide Photographic Materials

Polaritonic emission via surface plasmon cross coupling

In this letter the authors demonstrate that the emission of plasmon/exciton polaritons in an organic semiconductor can be extracted using surface plasmon cross coupling. A J-aggregated cyanine dye layer is deposited on a silver film and then the whole structure is periodically corrugated. As a result of this corrugation, the dispersion lines of the surface modes on both sides of the silver layer may cross. At this crossing point, an increase in the polaritonic emission is observed. The contributions of unpolarized incoherent states and of the TM polarized polaritons emission are separated.

Enhanced Intra-Aggregate Charge Separation from Binary Excitons in Mixed J-Aggregates of Cyanine Dyes

Well-ordered, two-dimensional, amalgamation-type J-aggregates consisting of two different kinds of structurally analogous anionic cyanine dyes were self-assembled on an amino-functionalized Au(111) electrode surface. Similar binary J-aggregates, though considerably less ordered in either one- or three-dimensional structure, could also be grown easily in a concentrated ( approximately 1.5 M) aqueous solution of NaCl. These binary J-aggregates are characterized by a singly peaked J-band associated with a unique molecular exciton shared by the two different dye components coherently. This cooperative binary excitonic state can live with substantial (more than 0.1 eV) energy gaps between the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels of the two dyes mixed together. These energy gaps allow the binary exciton to relax very rapidly to an intra-aggregate charge-separated state in good competition with the metal-induced quenching of the excited-state energy. The enhanced charge separation leads to a high-efficiency photocurrent generation with a simple binary J-aggregate-coated Au(111) electrode in a reversible redox solution and results in strong quenching of the fluorescence from the corresponding aggregate grown in solution free from substrate-induced quenching.