Dye LB Film Research Articles

Characteristics of Intramolecular Charge Transfer by J-Aggregates in Merocyanine Dye LB Films.

In this study, for the development of future molecular electronic devices, we have investigated the characteristics of the aggregates of Langmuir-Blodgett films. The characteristics of intramolecular charge transfer by J-aggregates in merocyanine dye LB films have been studied experimentally by using UV irradiation and heat treatment. In addition to intramolecular charge transfer, we also studied the conjugation and energy changes of the molecules. In case a dye is thinned by LB method, the alkyl chain is often displaced in order to form a mono-molecular film with ease. Since the molecular association form is often made by self-organization of molecules themselves, in case the dye and the alkyl chain are strongly bonded by the covalent bond, it may be said that the properties of the LB film to be built up are almost determined at the time of synthesis of film-forming molecules. Meanwhile, since, in case LB film is fabricated by the diffusion absorption method, the cohesive force between the water-soluble dye and the surface-active mono-molecular film is electrostatic, the dye molecule can move relatively freely on the air/water interface, which may be regarded as a two-dimensional crystal growth process.

Generation of disk-like domains with nanometer scale thickness in merocyanine dye LB film induced by hydrothermal treatment

We have characterized the binary LB films of merocyanine dye (MS) and arachidic acid (C20) before and after hydrothermal treatment (HTT), which is defined as a heat treatment under relative humidity of 100%, focusing on the morphology studied by bright field (BF) microscopy and fluorescence (FL) microscopy. BF microscopy observation has revealed that the as-deposited MS-C20 binary LB film is found to emit intense red fluorescence over the whole film area by 540-nm excitation. Since the surface image is almost featureless, it is considered that the crystallite sizes of J-aggregate are less than 10 μm. Interestingly, after HTT, round-shaped domains are observed in the LB systems, and the sizes are reaching 100 μm in diameter. Crystallites of J-aggregate, which are bluish in color and emit intense red fluorescence, tend to be in the round domains. We have observed two different types of domains, i.e., blue-rimmed domains and white-rimmed domains, which are postulated to be confined in the inner layers and located at the outermost layer, respectively. The thickness of the domains is equal to or less than that of the double layer of the MS-C20 mixed LB film, which is ca. 5.52 nm. The molecular order of MS in the J-aggregate is improved by the HTT process leading to the significant sharpening of the band shape together with the further red shift of the band (from 590 to 594 nm up to 597 to 599 nm). The reorganized J-band is considered to be ‘apparently’ isotropic owing to the random growth of the J-aggregate in the film plane. We consider that the lubrication effect by the presence of water molecules predominates in the HTT process.

Photolysis Properties of Merocyanine Dye LB Films by Various Time of UV Irradiation

We fabricated the merocyanine dye LB films with arachidic acid (MD LB films). We compared absorption peak of before and after added Cd2+. The optical absorption peak of the MD LB films was shifted to 610 nm at 535 nm, when Cd2+ ions were added. We also investigated the optical absorption peak of the LB films by various time at 365 nm UV. We confirmed J-aggregation and photolysis properties. This is that studied the application possibility of the switching device and the nonvolatile memory.

The monitoring of J-aggregate behavior of merocyanine dye based on electrochemical QCM

In this paper, the electrical behavior of a quartz crystal microbalance (QCM) with dye LB film in UV irradiation has been examined by the impedance analysis method. The equivalent electrical parameters, such as resonant frequency ( f 0) and resistance ( R 1), were investigated. The preparation conditions, using a mixing ratio of fatty acids, subphase effect, and π-A isotherms were investigated to obtain the J-aggregated dye LB film and its optical characteristics were evaluated by UV spectroscopy. The resonant frequency was originated without considering mass adsorption and dependence on the mixing ratio with arachidic acid or resultant absorbance peak at the J-band (optical characteristics). This result could be described by the observation of morphological change before and after UV irradiation, i.e. the resonant frequency shift had a connection with the morphological change. This result strongly suggests that the QCM can be applied to monitor the structural change or optical characteristics of an organic film on the QCM.

Enhancement of Second-Harmonic Response and Photocurrent Generation from a Benzothiazolium Styryl Dye LB Film through an Interfacial Self-Assembly Reaction

An interface self-assembly reaction between HgCl2 and an amphiphilic heteroaromatic styryl dye, 2-(4-dihexadecylaminostyryl) benzothiazole methiodide (I), was studied. Its Langmuir−Blodgett films Ia, Ib, and Ic fabricated from different subphases (pure water, 5 × 10-8 M HgCl2, and 5 × 10-7 M HgCl2, respectively) were characterized by using UV−vis spectra and XPS measurements. Compared to those of film Ia, the seond-harmonic responses and photocurrent generation from film Ib and Ic were obviously enhanced with the addition of HgCl2 into the subphase. Under ambient conditions (0.5M KCl), the quantum yields of photoelectric conversion are 0.73%, 0.95%, and 2.45% for Ia, Ib, and Ic respectively. The effects of some factors such as bias voltage, methyl viologen (MV2+) and hydroquinone (H2Q) on the photocurrent generation have also been investigated.

Effect of RuCl 3 subphase on second harmonic generation and photocurrent generation from a benzothiazolium styryl dye LB film

Langmuir–Blodgett film of an amphiphilic heteroaromatic styryl dye, 2-(4-dihexadecylaminostyryl) benzothiazole methiodide ( I), was fabricated from RuCl 3 subphases, and was characterized by using UV–VIS spectra and XPS measurements. Experimental data indicated that addition of RuCl 3 into subphase is favorable to the second harmonic generation of the films, but unfavorable to photocurrent generation from the film. Effects of some factors such as bias voltage, methyl viologen (MV 2+), O 2 and hydroquinone (H 2Q) on the photocurrent generation have also been investigated. Based on the experimental data, a possible scheme concerned effect of RuCl 3 on the SHG and photocurrent generation of the films was proposed.

The subtle role of heteroaromatics in the second-order susceptibility in a series of amphiphilic styryl dye Langmuir–Blodgett films

A series of amphiphilic styryl dyes: 2-(4-dihexadecylaminostyryl) benzothiazole methiodide (BTM), 2-(4-dihexadecylaminostyryl) benzoxazole methiodide (BOM), and 2-(4-dihexadecylaminostyryl) benzimidazole methiodide (BIM), were synthesized; their monolayers were successfully deposited on quartz slides by the Langmuir–Blodgett technique and formed H aggregates. Second-order susceptibilities χzzz(2) of the monolayers were determined with a polarized laser beam (Nd:YAG, λ=1.064 μm). The values of χzzz(2) are 215, 132, and 67 pm V−1 for BTM, BOM and BIM, respectively. Charge distributions over the entire molecules for the dye models were calculated using the MINDO/3 method in the MOPAC 7.0 program. Experimental data and semiempirical quantum chemical calculation results show that electron deficiencies of the heteroaromatic rings play an important role in determining the second harmonic generation of organic dye LB films.

The Influence of Counter Ions on the Morphology of Cyanine Dye Aggregates at the Air/Water Interface

In a cyanine dye LB film, the J-aggregates of the dye molecules form domain structure. The shape and size of this structure are largely influenced by the conditions of film fabrication. We made a through investigation about the effects of counter anions of the dye molecules and ions as additives in the subphase on the domain structure in dye monolayers at the air/water interfaces and in LB films by using a fluorescence microscope. We found the conditions under which we can promote or prevent the growth of the domains, and discussed the influence of anions on π-A isotherm.

Formation and Characterization of H-Like Band in Merocyanine Dye LB Films

The merocyanine-arachidic acid mixed LB films have been found to exhibit H-like band whose absorbance maximum is blue-shifted from that of monomer band. It is indicated that alkane molecules added to the mixed system induces the formation of H-like band.

Gas Detection by a Multi-Hybrid Sensor with Dye Langmuir-Blodgett Films Deposited on a Quartz Oscillator

Abstract A hybrid gas sensor combined an optical detector with a weighing system for adsorbed gas is realized by dye LB-films deposited on a quartz oscillator. With this sensor, the change of fluorescence intensity from dye LB-film is simultaneously measured with the change of oscillation frequency of the quartz oscillator which depends on the amount of adsorbed gas in the LB-film. Squarylium dye LB-film and perylene dye LB-film were applied for this hybrid gas sensor. The quartz oscillators with LB-film commonly showed decrement of their oscillation frequency corresponding to the adsorption of gases. On the other hands, changes of fluorescence intensity depend on the type of gases, the dye molecules and its aggregation forms. These results suggest advantage of a multi-hybrid gas sensor using multiple quartz oscillators with different dye molecules. In this report, we discuss the responses of hybrid gas sensor in connection with the semiconductivity of the dye and its aggregate in LB-films.

Single beam self-interaction in Langmuir-Blodgett films

Multiple diffraction rings are observed after a pulsed laser beam passes through an absorbing dye LB film. The theoretical analysis, based on the model of transverse self-phase modulation, is also given. The saturated nonlinear refractive index n 2 is estimated to be 2.0×10 −6 cm 2 W from the number of rings induced in the LB films. The main contribution to this larger nonlinearity is believed to be from laser-induced transformation between H-aggregates and monomers of molecules in the LB films.

Hybrid gas detector of squarylium dye Langmuir-Blodgett film deposited on a quartz oscillator

A hybrid gas detector combined optical detector with a weighing system for absorbed gas in Langmuir-Blodgett films deposited on a quartz oscillator is reported. With this detector, the fluorescence intensity change from a squarylium dye LB film containing J-aggregates and the amount of adsorbed gas in the dye LB film are measured simultaneously. Responses of this detector for NO 2, trichloroethylene, NH 3 were evaluated. On exposure to NO 2, the fluorescence was sharply quenched in correspondence with a decrement of oscillation frequency. The ratio of fluorescence quenching to the amount of adsorbed NO 2 gas molecules was estimated with two different signals from this hybrid gas detector. On the other hand, a slight increment of fluorescence was observed with a decrement of oscillation frequency after introduction of NH 3 gas. In the case of an organic solvent such as trichloroethylene, a decrement of oscillation frequency was observed without change of fluorescence intensity. trichloroethylene, a decrement of oscillation frequency was observed without change of fluorescence intensity.

Organic electroluminescent device with cyanine dye Langmuir-Blodgett film as an emitter

Double hetero-structure electroluminescent (EL) devices with a cyanine dye LB film as an emitter were prepared. The cyanine dye formed J-aggregate in the LB film, and intense fluorescence with very narrow bandwidth was observed in the LB film. When DC voltage was applied to the devices, EL corresponded well with the resonance fluorescence of the J-aggregated cyanine dye. As a result of confinement of charge carriers and excitons within the cyanine dye emitter, efficient electroluminescence was attained even in the device with the J-aggregated cyanine dye bimolecular layer as an emitter.