Excited Dye Molecules Research Articles

A generalized electrodynamics model for surface enhanced Raman scattering and enhanced/quenched fluorescence calculations

A generalized electrodynamics model is proposed to describe the enhancement and quenching of the fluorescence signal of a dye molecule placed near a metal nanoparticle (NP). Both the size of the NP and quantum yield of the dye molecule are crucial in determining the emission intensity of the molecule. Changing the size of the metal NP will alter the ratio of the scattering and absorption cross sections of the metal NP and consequently results in different enhancement or quenching effect to the dye molecule. A dye molecule with a reduced quantum yield indicates that the non-radiative channel is dominant in the decay of the excited dye molecule and the amplification of the radiative decay rate will be easier. In general, the emission intensity will be quenched when the size of the metal NP is small and the quantum yield of the molecule is close to unity. A significant enhancement factor will be obtained when the quantum yield of the molecule is small and the particle size is large. When the quantum yield of the dye molecule is less than 10−5, the model is simplified to the surface enhanced Raman scattering equation.

Near Infrared Fluorescence Enhancement by Local Surface Plasmon Resonance from Arrayed Gold Nanoblocks

The near infrared (NIR) fluorescence enhancement by local surface plasmon resonanoce from arrayed gold (Au) nanoblocks was investigated by NIR fluorescent dyes, IR780, immobilized in hydrophobic DNA thin film on glass substrates, to clarify the gap mode effect on the fluorescence enhancement. In the substrate with Dimer type Au nanoblock arrangement, average total fluorescence intensity was larger by 10.0, 2.4, and 12.4 times for non-polarized, P- and S- polarization as compared with that on a glass substrate alone, respectively. These findings suggested that enhancement of excitation light intensity at nanogap in the Dimer type Au nanoblock arrangement affected the fluorescence intensity. Average total fluorescence intensity, on the other hand, was smaller by 0.63 times as compared with that on a glass substrate alone in the checkerboard type Au array. It is suggested that the fluorescence quenching was caused by the energy transfer from the excited state of IR780 to Au nanoblocks or by the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks at the checkerboard arrangement. We have firstly achieved the NIR fluorescence enhancement by LSPR due to the gap mode.

Launching plasmonic Bloch waves with excited dye molecules

In this paper, we will demonstrate that excited dye molecules can be used to launch the plasmonic Bloch waves (PBWs) propagating at multi-metal–dielectric interfaces. The properties of the PBWs, such as wavevectors, propagating bands, the interface and grating period effect, were characterized by a leakage radiation microscope. Theoretical simulations were also carried out to reveal the properties of the PBWs and were consistent with the experimental results. What is more, experimental results reveal an interesting phenomenon: the PBWs launched by the excited dye molecules present different optical behaviors from those launched by far-field laser beams through attenuated total reflection. The mechanism of this difference was analyzed based on the energy conversion between the optical near-field and far-field. Our work provides a new way to launch the PBWs. Further, the coupling between the dye molecules and PBWs also demonstrates a new method to manipulate the fluorescence emission from random to controllable.

Establishing the regularities and modelling the diffusion regime of random lasing in strongly scattering media

This paper describes how the experimental dependences of the energy parameters and the random lasing (RL) spectrum in the diffusion regime depend on the pump intensity, the concentration and refractive index of the scattering particles, the thickness of the sample, and the reflection at its boundaries. An algorithm is proposed for calculating these RL characteristics in the diffusion regime of light propagation by the Monte Carlo method, and calculated dependences of these RL characteristics on the parameters of the medium are obtained that agree with the experiment. It is shown that, because of reflection from the sample boundaries, there is an optimum thickness of the sample for which the RL energy is maximal, and its spectrum is narrowest. The dynamics of the number of excited dye molecules and the photons that they emit in a sample are calculated, along with the RL spectrum as a function of time. The existence of three stages in the formation of RL is established: accumulation of excited molecules, formation of multimode radiation, and relaxation with persistent lasing in high-Q modes. It is shown that the dominant role in the formation of RL radiation is played by the highest-Q modes.

Quantitative Comparison of Five Different Photosensitizers for Use in a Photopolymer

Several studies of the time varying photon absorption effects, which occur during the photoinitiation process involving in photopolymer materials, have been presented. Three primary mechanisms have been identified: (i) the dye absorption, (ii) recovery, and (iii) bleaching. Based on an analysis of these mechanisms, the production of primary radicals can be physically described and modelled. In free radical photopolymerization systems, the excited dye molecules induce the production of the primary radicals, R•, which are key in determining how many monomers are polymerized. This, in turn, is closely related to the refractive index modulation formed during holographic recording. In this paper, to avoid the complexities involved in estimating the rate constant of intersystem crossing, kst, in going from the excited singlet state dye to the excited triplet state dye, we introduce two rates, kaS and kaT these are the proposed rate constants of photon absorption in going from the ground state to the singlet and triplet states, respectively. Using the resulting model, four kinds of Xanthene dyes: Erythrosin B; Eosin Y; Phloxine B, Rose Bengal, and one Thiazine dye: Methylene Blue, are experimentally characterised for use in an AA/PVA photopolymer.

The Study of Dynamic Behaviour of Transient Grating in Azo Dye Doped Nematic Liquid Crystal

In this experimental work, we investigated the dynamic behaviour of the transient holographic grating in an Azo dye doped nematic liquid crystal, formed by a pulsed laser. Relaxation behaviour of the grating was studied in two experimental geometries, when the director is parallel or perpendicular to the grating vector. Relaxation time constants for different writing angles were used to measure the diffusion coefficients. The obtained results show the anisotropic diffusion of the photo excited dye molecules.

Similar Device Architectures for Inverted Organic Solar Cell and Laminated Solid-State Dye-Sensitized Solar Cells

Here, we examine the device architecture of two different types of solar cells mainly inverted organic solar cells and solid state dye-sensitized solar cells (DSSCs) that use organic materials as hole transportation. The inverted organic solar cells structure is dominated by work on titanium dioxide () and zinc oxide (ZnO). These layers are sensitized with dye in solid state DSSCs. Because of the similar device architecture, it becomes possible to fabricate laminated solid-state DSSCs. The performance of the device was improved by varying the top metal electrode. In laminated solid-state DSSC, we expect that excited dye molecules inject electron into the conduction band of nanocrystalline layer, whereas P3HT provides efficient hole transportation. These solar cells are promising for future energy source as they are cheaper, light weight, flexible and made into large areas, which are showing growing importance.

Formation of N719 Dye Multilayers on Dye Sensitized Solar Cell Photoelectrode Surfaces Investigated by Direct Determination of Element Concentration Depth Profiles

The structure of the dye layer adsorbed on the titania substrate in a dye-sensitized solar cell is of fundamental importance for the function of the cell, since it strongly influences the injection of photoelectrons from the excited dye molecules into the titania substrate. The adsorption isotherms of the N719 ruthenium-based dye were determined both with a direct method using the depth profiling technique neutral impact collision ion scattering spectroscopy (NICISS) and with the standard indirect solution depletion method. It is found that the dye layer adsorbed on the titania surface is laterally inhomogeneous in thickness and there is a growth mechanism already from low coverage levels involving a combination of monolayers and multilayers. It is also found that the amount of N719 adsorbed on the substrate depends on the titania structure. The present results show that dye molecules in dye-sensitized solar cells are not necessarily, as presumed, adsorbed as a self-assembled monolayer on the substrate.

Electrochemical impedance parameters elucidate performance of carbazole–triphenylamine–ethylenedioxythiophene-based molecules in dye-sensitized solar cells

Abstract Organic dyes are synthesized containing bridging ethylenedioxythiophenes (EDOT) between the electron donors and electron acceptors (2-cyanoacetic acid) on carbazole–triphenylamines. These compounds are then characterized by photophysical, electrochemical, and theoretical computational methods. Nanocrystalline TiO 2 -based dye-sensitized solar cells (DSSCs) are fabricated using these dye molecules as light-harvesting sensitizers. The overall efficiency of the sensitized cells is high (5.20%) compared to the efficiency of a cis-di(thiocyanato)-bis(2,2′-bipyridyl)-4,4′-dicarboxylate ruthenium (II) (N3 dye)-sensitized device (7.57%) fabricated and measured under the same conditions. The dye (ETPA3) containing one carbazole, two EDOT bridges, and two 2-cyanoacetic acid groups appears to assist in the charge transfer from the excited dye molecules to the conduction band of TiO 2 , leading to the higher efficiency of the devices using assembled with this dye. A supplementary study of the electrochemical impedance supports the enhancement of the charge transfer of TiO 2 (e − ) with the ETPA3 dye. A computational examination of the ETPA3 compound also indicates higher charge transfer efficiency in the electronically excited state.

Charge transport at the metal oxide and organic interface

This review focuses on electron transfer at the interfaces between metal oxides and dye molecules within the context of the chemical nature of the anchoring functional groups, the structure of the dye molecules and the morphology of the metal oxides. In dye-sensitized metal oxides, the efficiency of interfacial charge separation and hence photon-to-current conversion may be sensitively manipulated by the interfacial bonding interactions whereby the dye molecules are adsorbed onto the oxide surface, as well as by the oxide surface morphologies. In these studies, it has been found that upon photoirradiation, the electron injection from the excited dye molecules into the conduction band of metal oxides and electron transport in the metal oxide are two of the most important steps. Therefore, a fundamental understanding of how the interfacial electron transfer dynamics is impacted by these structural parameters is critical for the design and optimization of dye-sensitized photocatalysis and photovoltaics.

Synergistic effect of surface plasmon resonance and constructed hierarchical TiO2 spheres for dye-sensitized solar cells

We demonstrate a strategy for incorporating plasmon resonant metallic nanoparticles in the construction of hierarchical TiO(2) spheres. Localized electric fields can be produced by the addition of Au nanoparticles, which can excite dye molecules more effectively than incident far-field light. The synergistic effect of surface plasmon resonance with constructed TiO(2) nanostructures has been investigated, and was confirmed by optical spectroscopy, J-V characteristics, EIS analysis and OCVD measurements. When Au nanoparticles are incorporated into the constructed TiO(2) spheres, the device achieves a power conversion efficiency of 6.62%, a 4.6% increase compared to the device based on constructed TiO(2) spheres without plasmon resonant Au nanoparticles, and a 17.4% increase compared to that without any treatment.

Charge transport properties in nanocomposite photoanodes of DSSCs: crucial role of electronic structure

TiO 2 nanorods, TiO 2 nanorod/TiO 2 nanoparticle and TiO 2 nanorod/ZnO nanoparticle composite structures were integrated as photoanodes in backside illuminated dye-sensitized solar cells (DSSCs). Incorporation of TiO 2 nanoparticles into the bare nanorods increased the dye loading and improved the short-circuit current density ( J sc ) from 2.22 mA/cm 2 to 3.57 mA/cm 2 . ZnO nanoparticles electrochemically grown into the TiO 2 nanorod layer could increase the surface area. Nevertheless, this considerably reduced the J sc to 0.57 mA/cm 2 and consequently cell efficiency. Electrochemical impedance spectroscopy (EIS) results showed that ZnO incorporated samples have better effective diffusion coefficient of electrons in comparison with bare TiO 2 nanorods while the recombination rate of injected electrons to photoanode with electrolyte is near eight times faster than bare TiO 2 nanorods. ZnO incorporated samples showed lower electron density at steady state in the conduction band also. The worse performance of ZnO incorporated samples was attributed to lower electron injection efficiency from excited dye molecules. Monitoring electron transport properties of the cells measured by EIS pointed out the crucial role of electronic structure of composite film components on the performance of cells. Our results showed that EIS technique could be used as an efficient characterization method for precise monitoring of charge transport in nanocomposite photoanodes for DSSCs.

Chemical Conversion Synthesis of ZnS Shell on ZnO Nanowire Arrays: Morphology Evolution and Its Effect on Dye-Sensitized Solar Cell

Heterostructured ZnO/ZnS core/shell nanowire arrays have been successfully fabricated to serve as photoanode for the dye-sensitized solar cells (DSSCs) by a facile two-step approach, combining hydrothermal deposition and liquid-phase chemical conversion process. The morphology evolution of the ZnS coated on the ZnO nanowires and its effect on the performance of the DSSCs were systematically investigated by varying the reaction time during the chemical conversion process. The results show that the compact ZnS shell can effectively promote the photogenerated electrons transfer from the excited dye molecules to the conduction band of the ZnO, simultaneously suppress the recombination for the injected elelctrons from the dye and the redox electrolyte. As reaction time goes by, the surface of the nanowires becomes coarse because of the newly formed ZnS nanoparticles, which will enhance the dye loading, resulting in increment of the short-circuit current density (J(SC)) . Open-circuit photovoltage decay measurements also show that the electron lifetime (τ(n)) in the ZnO/ZnS core/shell nanostructures can be significantly prolonged because of the lower surface trap density in the ZnO after ZnS coating. For the ZnO/ZnS core/shell nanostructures, the J(SC) and η can reach a maximum of 8.38 mA/cm(2) and 1.92% after 6 h conversion time, corresponding to 12- and 16-fold increments of as-synthesized ZnO, respectively.

Fluorescence enhancement of dye-doped liquid crystal by dye-induced alignment effect

We investigated fluorescence from hemicyanine dye molecules in a liquid crystal (4,4′-n-pentylcyanobiphenyl) (5CB) medium at different temperatures. The fluorescence decay lifetime decreased monotonically irrespective of the thermodynamic phases of the host medium as the temperature was increased. This behavior is due to an intramolecular motion of the dye promoted with the decrease in the viscosity of the medium facilitating a nonradiative decay of the excited dye molecules. By contrast, fluorescence intensity from the dyes in the nematic phase was about 3 times stronger than that in the crystalline or isotropic phase. This fluorescence enhancement in the nematic phase was found to be due to an anisotropic alignment of the dye molecules following the anisotropic alignment of the host liquid crystal medium along the pump-beam polarization direction. This light-induced liquid crystal molecular alignment was markedly enhanced by the guest dyes preferentially excited along the pump-beam polarization direction. The orientational order parameter of the dyes in the liquid-crystalline phase deduced from fluorescence anisotropy measurement was similar to the known order parameter of the liquid crystalline 5CB.

Performance variation from triphenylamine- to carbazole–triphenylamine–rhodaniline-3-acetic acid dyes in dye-sensitized solar cells

Organic dyes have been synthesized which contain an extra-electron donor (carbazole) and electron acceptors (rhodaniline-3-acetic acid) on triphenylamines (TPA). Photophysical, electrochemical, and theoretical computational methods have categorized these compounds. Nanocrystalline TiO 2-based dye-sensitized solar cells (DSSCs) are fabricated using these dye molecules as light-harvesting sensitizers. The overall efficiency of sensitized cells has 4.64% relative to a cis-di(thiocyanato)-bis(2,2′-bipyridyl)-4,4′-dicarboxylate ruthenium (II) (N3 dye)-sensitized device (7.83%) fabricated and measured under the same conditions. Carbazole-electron donation in the dye molecules plays a key role in the increased efficiency. Two rhodaniline-3-acetic acid groups appear to help convey the charge transfer from the excited dye molecules to the conduction band of TiO 2, leading to a higher efficiency of devices using such a dye. Electrochemical impedance supports this dye's effect on enhancing charge transfer in TiO 2 (e −). Computations on this dye compound also indicate the larger charge transfer efficiency in the electronically excited state.

Modifying photoisomerization efficiency by metallic nanostructures

Trans-to-cis photoisomerization efficiency of azobenzene dye is artificially modified from 0.09 to 0.38 when dye molecules are placed close to gold nanoparticle films with different structures. Transient fluorescence and surface enhanced Raman scattering measurement verify that the enhancement and reduction of photoisomerization efficiency come from the competition between enhanced local optical field from surface plasmon resonance and the accelerated nonradiative decay of excited dye molecules. The photoisomerization efficiency can be further modified by controlling the distance between azobenzene dye and gold films. Our finding can be applied to improve the performance of photoisomerization effect in photochemistry and photonics.

Polarization Dependence for Enhancement of Near-Infrared Fluorescence Intensity by Local Surface Plasmon Resonance from Arranged Gold Nanoblocks

The polarization dependence of excitation light for fluorescence enhancement of near-infrared dyes immobilized in hydrophobic DNA thin film on glass substrates with regularly arranged Au nanoblocks was investigated. The enhancement factor for S-polarized excitation was about 1.2 to 1.5 times as large as that for P-polarized excitation. P-polarized light contributed to the excitation of plasmon band both of horizontal and vertical direction of Au nanoblocks. The vertical direction corresponds to the short axis for height direction which has the absorption in visible region did not contribute the excitation of IR780. When the absorption band of Au array and the fluorescence band of IR780 were overlapped, the fluorescence enhancement did not depend on the polarization of excitation light. It is suggested that the fluorescence quenching originates from the energy transfer from the excited state of IR780 to Au nanoblocks or the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks.

Chemiluminescence during interaction of 1,2,4-trioxolanes and 1,2,4,5-tetraoxanes with iron compounds

The reaction of triterpene 1,2,4-trioxolanes with the system FeCl3-L-cysteine hydrochloride in the presence of rhodamine G is accompanied by chemiluminescence, whose emitter is an excited dye molecule. Light emission was also found in the biologically important reaction of 1,2,4,5-tetraoxanes with Fe2+ ions in aqueous acetonitrile.

Probing colloidal interfaces by angle-resolved second harmonic light scattering

We report angle-resolved second harmonic light scattering from bare colloidal particles in water. A nonlinear Mie model is used to quantitatively analyze the nonresonant second harmonic (SH) scattering profiles and to determine the elements of the local second-order surface susceptibility. The SH signal is attributed to oriented and electrically polarized water molecules at the charged particle interface. The results show how angle-resolved SH light scattering can be applied to probe not only resonant excited dye molecules but also nonresonant molecules such as water at the interface of colloidal particles.

Optimization of Multiple Electron Donor and Acceptor in Carbazole-Triphenylamine-Based Molecules for Application of Dye-Sensitized Solar Cells

Organic dyes have been synthesized which containing multiple electron donors (carbazole) and electron acceptors (rhodaniline-3-acetic acid) on triphenylamine (TPA). Photophysical, electrochemical, and theoretical computational methods have categorized these compounds. Nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs) are fabricated using these dye molecules as light-harvesting sensitizers. The overall efficiency of sensitized cells is high (4.64%) as compared to a cis-di(thiocyanato)-bis(2,2′-bipyridyl)-4,4′-dicarboxylate ruthenium(II) (N3 dye)-sensitized device (7.83%) fabricated and measured under the same conditions. Both electron donor (carbazole) and acceptor (rhodaniline-3-acetic acid) play a key role in the increased efficiency. One carbazole and two rhodaniline-3-acetic acid-based dye appears to help convey the charge transfer from the excited dye molecules to the conduction band of TiO2, leading to a higher efficiency of the assembled devices using such a dye. Electrochemical impedanc...