J-aggregates Of Dyes Research Articles

Kinetics study of ultrafast electron transfer from sensitized dyes to silver halide microcrystals

Spectral sensitization micromechanism of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr microcrystals with different dye concentrations is studied by using picosecond time-resolved fluorescence spectroscopy and the dependences of electron transfer and spectral efficiency sensitization on different conditions are analysed in detail. With the steady spectroscopy, the wavelengths of absorption and fluorescence of J-aggregate adsorbed on AgBr microcrystals are found to shift to red relative to dye monomer. The spectrum of fluorescence has a red shift relative to the absorption peak. With the time-resolved fluorescence spectroscopy, the fluorescence decay curves of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr grains are found to be fitted well by a double-exponential decay function. The fitting curves consist of a fast and a slow component. Because of the large amplitude of the fast component, this fast decay should be attributable mainly to the electron transfer from J-aggregate of dye to a conduction band of AgBr.

Molecular exciton theory calculations based on experimental results for Solophenyl red 3BL azo dye–surfactants interactions

The influence of anionic surfactant: sodium dodecyl sulfate (SDS) and cationic surfactants: cetyltrimethylammonium bormides (C 16TAB) and cetylpyridinium chloride (CPC) on the electronic spectrum of Solophenyl red 3BL azo dye (C.I. Direct 80) in aqueous solution was studied by means of UV–vis spectroscopy. Since, Solophenyl red 3BL azo dye was an anionic soluble dye, therefore, did not observed any interaction between SDS and 3BL dye. On the other hand, in the case of C 16TAB, aggregation was reflected by a hyosochromic shift of the main absorption band and dye H-aggregation was responsible for the short wavelength absorption band. Also, UV–vis spectra showed that micelle formation occurs for C 16TAB surfactant in 3BL dye aqueous solution in lower concentration in comparison with C 16TAB in aqueous solution lonely. Micelle formation was indicated by a red shift of the whole spectra with respect to monomer location. The importance of hydrophobic interactions was revealed by the dependence of aggregation on the cationic surfactant structure. Further results showed that dye H-aggregation was occurred under the cationic surfactant CPC as well, but in this case micelle formation could not occur. Addition of CPC surfactant into the J-aggregate dye solution in highly acidic aqueous solution was also caused completely disaggregating of dimer molecules, which may be related to occuring an acid–base reaction between them. Applicability of the molecular exciton (Kasha) theory in order to interpret of aggregation results and to estimate dimer structure of 3BL dye under C 16TAB and CPC surfactants addition was very poor and the calculated data based on this model showed that this simple point-dipole model could not describe our experimental results.

Study of strong coupling between surface plasmon and exciton in an organic semiconductor

In this paper the optical properties of thin films comprising J-aggregated dyes (TDBC) in a polymeric matrix (PVA) deposited on a metallic (silver) layer are studied. Angular reflectometry experiments are conducted in order to obtain the dispersion energy curve of the Surface Plasmon (SP) in relation with the exciton mode. It exhibits an anticrossing behavior characteristic of the strong coupling regime. Simulations using a transfer matrix method with complex optical indices are applied and discussed. They show a roughly good agreement with the experimental results and allow us to estimate the value of the oscillator strength of organic J-aggregate semi conductors used in our experimental studies.

Anisotropic observation of absorption and fluorescence transition dipoles in exciton–polariton properties of PIC J-aggregates

Fibril-shaped J-aggregates of pseudoisocyanine dyes are prepared in thin-film matrices of polyvinyl sulfate and their microscopic fluorescence and reflectance imaging are investigated at room temperatures. Improved experiment, both in sample preparations and in microscope optics, allows us to resolve the higher-energy bands in the spectrum and to determine the directions of local absorption and fluorescence transition dipoles more precisely. Based on the anisotropies of the local transition dipoles, we have assigned the 540 nm middle band to be the upper exciton, Davidov split, transition and the higher 495 nm to its vibronic sub-band, while the J-band at 572 nm to be the lower Frenkel exciton transition. Assuming linear chain directions of individual J's to be parallel in average to the long axis of the fibril, the result also implies that a zigzag-type molecular conformation is most suitable for the model of PIC-J aggregates.

Self-localization of excitons in a periodically modulated molecular medium

Electromagnetic field propagation is analyzed in a one-dimensional Bragg grating consisting of periodically arranged linear molecules making up a resonant medium. Dye J-aggregates and conjugated polymers are considered as examples of the medium. Both adiabatic and nonadiabatic dynamics of the acoustic waves generated by electromagnetic field in the system are examined. The effects of exciton-phonon and exciton-phonon-photon interactions on the band structure and formation of self-localized excitations are examined on various time scales. A new mechanism for controlling bandgap parameters in a bistable regime is described. Some effects of electromagnetic-field nonuniformity on generation of phonons in molecules and exciton self-localization are investigated.

Spectroscopic properties of persistence-type dye aggregate in wide temperature range

Spectroscopic properties of the monolayer assemblies, S9(J) + S11(J), which incorporate the mixed J-aggregate (JA) of oxacyanine dye; N, N′-dioctadecyl-oxacyanine perchlorate (S9) and thiacyanine dye; N, N′-dioctadecyl-thiacyanine perchlorate (S11), have been studied in the wide temperature range of T = 6.0–293 K. The mole fraction X of S11, X = [S11]/([S9] + [S11]), in the S9(J) + S11(J) assemblies has been varied from 0 to 1. At room temperature, absorption and fluorescence spectra of the monolayer assemblies incorporating the individual dye aggregate, S9 J-aggregate (S9(J)) or S11 J-aggregate (S11(J)), are characterized by a distinct J-band and resonance fluorescence. The S9(J) + S11(J) assemblies with X = 0.1–0.9 display two absorption bands; shorter-wavelength (SW) band and longer-wavelength (LW) band and a single fluorescence band (LW-fluorescence). With lowering temperature, the blue shift and narrowing of the absorption bands are observed. The low-energy tails of the J-band of the S9(J) ( X = 0) and the S11(J) ( X = 1) assemblies, as well as the LW-band of the S9(J) + S11(J) assemblies obey the Urbach–Martienssen (U–M) rule. The steepness parameter σ versus T curves show characteristic changes caused by mutual mixing of S9 and S11, which would supply us with a supporting evidence for the formation of the homogeneous aggregate of persistence-type (HP-aggregate) in the S9(J) + S11(J) assemblies.

Photo-induced reduction of Noble metal ions to metal nanoparticles on tubular J-aggregates

Palladium and silver nanoparticles are formed on the surface of tubular J-aggregates of an amphiphilic tetrachlorobenzimidacarbocyanine dye by reduction of the respective metal cations in aqueous solution. Upon addition of the palladium complex Na2PdCl4to the aggregate solution, the absorption spectrum shows significant changes which is explained by partial destruction of the aggregates. Cryogenic transmission electron microscopy (cryo-TEM) images show that the tubular J-aggregates are randomly covered by well-separated Pd nanoparticles of approximately 1–3 nm size. Larger particles and higher particle density along the aggregates are obtained when an auxiliary reducing agent is added to the solution. The presence of the metallic particles leads to efficient fluorescence quenching giving clear evidence for super quenching. In similar experiments using AgNO3, silver nanoparticles are grown which are larger in size but less dense distributed along the aggregates. At least in the case of the silver particles, the spontaneous formation of metal nanoparticles is assumed to be initiated by a photo-induced electron transfer process (PET).

真空蒸着膜におけるビスアゾメチン色素のJ会合体

真空蒸着膜におけるビスアゾメチン色素のJ会合体

Super-Helix Formation Induced by Cyanine J-Aggregates onto Random-Coil Carboxymethyl Amylose as Template

The J-aggregation of Cyanine-1dye in the presence of carboxymethyl amylose (CMA) is described. The J-aggregation requires a large excess CMA concentration; the J-band maximum appears in the concentration range, [CMA]/[dye] = 10-50, depending on the degree of substitution (DS) of carboxylation, where [CMA] is the concentration of polymer repeat units. An extraordinarily large induced circular dichroism (CD) is observed from J-aggregates of the achiral cyanine dye in association with a random coil CMA, suggesting that the CMA is transformed into a helix. The magnitude of CD intensity increases with increasing DS of CMA and pH up to neutral (where a maximum J-aggregation occurs), while the CMA-bound dye monomer and H-aggregates (occurring at pH > or = 9) exhibit no induced CD. The trend in the CD intensity (of the J-aggregates) is in parallel with the fluorescence intensity of the J-aggregates. This suggests that binding of the J-aggregates onto the template CMA is sterically controlled by the asymmetric environment of glucose residues (of CMA) so that more twisting power is exerted with increasing DS (of CMA), rendering the cyanine dye/CMA complex a more rigid (a high fluorescence intensity) super-helix. This is also revealed by the AFM image of a long strand.

Formation of J-aggregates of mixed merocyanine dyes in Langmuir–Blodgett films

The formation and stability of J-aggregates of a [6Me-DS] 1− x [DO] x mixed dye system in Langmuir–Blodgett films have been investigated using absorption and photoluminescence measurements. The variations of the spectral weights of the J-aggregate and DO monomer bands with DO content x allowed us to find that there exist two different regions: phase separation and solid solution. For 0 ≤ x ≤ 0.3, J-aggregates are formed from 6Me-DS molecules, and DO molecules exist as a monomer. In the range 0.4 ≤ x ≤ 0.8, J-aggregates are stably formed from both 6Me-DS and DO molecules. We have also found that the quantum efficiency of the J-aggregate emission for x = 0.6–0.7 is higher than for the pure 6Me-DS dye system.

Optical nonlinearity of J-aggregates in vapor-deposited films of a bisazomethine dye

The third-order optical nonlinearity of the J-aggregates of nonionic dye in vapor-deposited films has been investigated in terms of electroabsorption measurement. Compared with that of a monomer film of the dye, the nonlinearity was enhanced by a factor of 4000. However, the number of aggregates in the J-aggregate film was estimated to be only a few. The obtained enhancement is mainly caused by the concentration of oscillator strength on the J-band and not by the development of the coherence size of excitons. Therefore, a much larger optical nonlinearity can be expected in highly ordered J-aggregates of the nonionic dye, and it is demonstrated that J-aggregate formation is an effective strategy for nonionic dye to improve its optical nonlinearity.

INFRARED PHOTOREFRACTIVE COMPOSITES BASED ON POLYIMIDE AND J-AGGREGATES OF CYANINE DYE

Photorefractive composites sensitive to 1064 nm on a base of an aromatic polyimide containing J-aggregates of a thiacarbocyanine dye are presented. The molecules of the dye form the nanocrystalline J-aggregates that are responsible for photoelectric sensitivity at 1064 nm and nonlinear third-order optical properties. The net gain coefficient 266 cm-1 and the response time 0.09 s were achieved at an external electric field of about 15 V/μm.

Fast Charge Transport in Nanocomposite Polymer Materials Containing J-Aggregates

ABSTRACT Charge transport in polymers containing J-aggregates of cyanine dyes serving as fast transport channels is considered. Shape of photocurrent transient depends on initial spatial distribution of carriers. If carriers are homogeneously generated at the electrode surface, then at the initial stage current raises reflecting carrier collection to fast channels and corresponding rate constant is determined by channel density.

Strong exciton-photon coupling in a length tunable optical microcavity with J-aggregate dye heterostructures

We report the incorporation of thin films of a cyanine dye J aggregate into a versatile, length tunable, optical microcavity. The dense J-aggregate layers give an optical response that can be modified by embedding them at specific positions within heterostructures of dielectric and metal layers. The microcavities are composed of separate gold mirrors, which can be individually nanopositioned, and give sharp resonant modes in the red/near-infrared region of the spectrum. With the dye layer favorably placed, anticrossing behavior is observed as the cavity modes are successively swept through the absorption resonance. Large Rabi splittings of up to 170meV are achieved at room temperature, agreeing well with predictions from a transfer-matrix model. These strongly coupled microcavities pave the way for microelectromechanical systems-integrated microdevices with tailored nonlinear optical properties.

Luminescence Properties of the Mixed J-Aggregate of Oxacyanine Dye and Thiacyanine Dye. Formation of a Persistence-Type Aggregate

The monolayer assemblies incorporating the J-aggregates of oxacyanine dye, N,N'-dioctadecyloxacyanine perchlorate (S9), and thiacyanine dye, N,N'-dioctadecylthiacyanine perchlorate (S11), S9(J) + S11(J), have been fabricated by the Langmuir-Blodgett (LB) technique. The mole fraction X of S11, X = [S11]/([S9] + [S11]), was varied from 0 to 1. Steady-state absorption spectra, fluorescence spectra, and picosecond fluorescence decay curves of the monolayer assemblies have been measured. Spectroscopic properties of the monolayer assemblies incorporating the individual dye aggregates, S9 J-aggregate (S9(J), X = 0) or S11 J-aggregate (S11(J), X = 1), are characterized by a distinct J-band and resonance fluorescence at lambda(ab) = 403 nm and lambda(em) = 403 nm for S9(J) and lambda(ab) = 456 nm and lambda(em) = 463 nm for S11(J). On the other hand, absorption spectra of the S9(J) + S11(J) assemblies for X = 0.1-0.9 display two absorption bands, a shorter wavelength one and a longer wavelength one, whose peak positions are blue-shifted from those of the corresponding J-bands of the S9 J-aggregate and the S11 J-aggregate, respectively. Furthermore, fluorescence spectra are characterized by a single band (longer wavelength fluorescence) which is somewhat blue-shifted from the resonance fluorescence of the S11 J-aggregate. The fluorescence lifetimes of the S11 J-aggregate and isolated S11 molecules in LB films appear to be tau = 110 and 1900 ps, respectively, while the fluorescence lifetime of the longer wavelength fluorescence of the S9(J) + S11(J) assemblies takes practically a constant value of tau = 170-180 ps for X = 0.2-0.8. These observations would indicate that S9 and S11 molecules in the S9(J) + S11(J) assembly can form a specific mixed aggregate distinct from the individual S9 and S11 J-aggregates. From detailed considerations of the former works on luminescence properties of the S9 J-aggregate doped with isolated S11 molecules, as well as the mosaic-type mixed J-aggregate (M-aggregate) composed of a certain thiacyanine dye, 3,3'-disulfopropyl- 5,5'-dichlorothiacyanine sodium salt, and thiacarbocyanine dye, meso-substituted 3,3'-disulfopropyl-5,5'-dichlorothiacarbocyanine potassium salt, it is suggested that S9 and S11 can form a homogeneous aggregate of the persistence type (HP-aggregate). The HP-aggregate is distinguished from the M-aggregate because it is characterized by homogeneous mixing of two component dyes and persistence of two absorption bands.

Photoluminescence properties of vapor deposited films of a bisazomethine dye

Steady-state and time-resolved photoluminescence (PL) measurements on vapor deposited films of a non-ionic bisazomethine dye have been performed. In the films, it is possible to control the ratio between J-aggregate and crystalline phases of the dye by means of exposure to chloroform vapour, and thus the origin of PL can be determined from comparison between several films. In the films, PL was emitted exclusively from the crystalline phase. Although the origin of PL was not from the J-aggregate phase, some features of the observed PL were very similar to those reported for J-aggregates of ionic dyes. We also found that these features in the vapor deposited films were caused by a competition between free excitons and excitons trapped at defect sites.

Up-converted luminescence of cyanine dye J-aggregates

A J-band photoluminescence of cyanine dye J-aggregates was observed under excitation below the band gap. This emission is not due to two-photon absorption. The luminescence intensity becomes weaker with a decrease in temperature. For the excitation below the band gap, the rise and decay times of the J-band luminescence from cyanine dye concentration of 4×10 −4 M are 9.0 and 155 ps, respectively. In case of the band-to-band excitation, the radiative decay starts just after excitation and fast and slow decay components have time constants of 13 and 54 ps, respectively. The lifetime of luminescence depends on the concentration of the cyanine dye.

J-Aggregates of Cyanine Dyes in Aqueous Solution of Polymers: A Quantitative Study

The effect of polyvinylsulfate (PVS) on the spectroscopy of the cyanine dye, 1,1’-diethyl-2,2’-cyanine iodide (PIC), has been investigated using UV-vis spectroscopy. J-aggregates of the PIC dye were formed upon addition of PVS to the monomers of the dye in solution. The appearance of only one isosbestic point in the UV-vis spectra suggests that the dye monomers are quantitatively converted to J-aggregates and equilibrium was reached. Using Benisi-Hildebrand kinetics, aggregation number of 4 was calculated for the dye. In addition, a 1:2 mole ratio of PIC/PVS was calculated at the maximum capacity of the polymer.

PASSIVE MODE LOCKING OF A Nd3+:YAG LASER WITH A SATURABLE ABSORBER IN THE FORM OF THIN FILMS OF J-AGGREGATES

A novel type of a saturable absorber for passive mode locking was proposed. As the novel saturable absorber, we studied the thin solid films of the molecular J-aggregates of polymethyn dyes. The films of the J-aggregates were prepared using different polymethyn dyes. Linear and nonlinear optical properties of these films were investigated. Passive mode locking using these films as the saturable absorber was performed in a Nd 3+: YAG laser. Stable generation of short pulses (pulse duration 13 ps) was achieved.

Third-harmonic generation in J-aggregates of a cyanine dye immobilised in a polymer matrix

Third-harmonic generation is obtained for the 1245-nm laser radiation in monolayers of J-aggregates of a cyanine dye in a diallydimethylammonium chloride polymer matrix. The third-order susceptibility of J-aggregates is two orders of magnitude higher than that of fused silica. The wavelengths of fundamental and third-harmonic radiation lie in the transparency region of the material.