Langmuir-Blodgett Films Of Merocyanine Dye Research Articles

Optical and Electrical Properties of Merocyanine Dye LB Films by Various Time of UV Irradiation and Heat Treatment

The Langmuir-Blodgett (LB) technique provides many possibilities for the control of film thickness, dimensions, and molecular structures on the nanometer scale. Various kinds of dye molecules have been found to form the J-aggregation which has been used as sensitizers of silver halide photography for long time. In recent years, they attract attention as model systems for investigating the ultra-fast exciton dynamics, materials for ultra-fast nonlinear optical devices, fluorescence probes for mitochondrial membranes. We fabricated the merocyanine dye LB films with arachidic acid (AA). In order to observe the J-aggregation of the merocyanine dye LB films, CdCl2 and KHCO3 solutions were added in subphase. From the optical absorption spectra of the mixed dye LB films (6Me-Ds:AA = 1:2) at different layers, the optical absorption peak was about 520 nm. However, the optical absorption peak of the LB films was shifted to 600 nm, when CdCl2 and KHCO3 solutions were added. This is the consequence result to the J-aggregation of the merocyanine dye. We also investigated the optical absorption peak of the LB films according to various time at 60 degrees C and 275 nm UV. We measured the STM morphology of the merocyanine dye LB film (1 layer) before UV irradiation and heat treatment. The morphology size of the LB film on HOPG was 5 nm. The roughness and molecular size were about 66.163 pm and 0.176 nm, respectively. The J-aggregation of this type was also accompanied by large morphological changes. We analyze the morphology and electrical properties of the LB films by the scanning tunneling microscopy (STM).

Modification of optical characteristics in langmuir-blodgett films of merocyanine dye by reduced pressure treatment

We have modified the optical characteristics of various aggregation states including J- and H-aggregates in Langmuir-Blodgett(LB)films of merocyanine dye(MS)by reduced pressure treatment. The J-band peaks at 590 nm almost remain unchanged after the treatment. On the other hand, the peaks of blue-shifted bands involving the H-band at 505 nm drastically diminish, resulting in the formation of the broad bands having the absorption maximum at 530-540 nm with the bands showing in-plane isotropy. The results indicate the dissociation of the MS aggregates. Therefore, the MS blue-shifted aggregates were found to dissociate easily by the reduced pressure treatment.

The spectroscopic and morphological behavior of merocyanine dye Langmuir–Blodgett films

Abstract We fabricated the optical system of merocyanine dye (MD) using the Langmuir–Blodgett (LB) method with various mixing ratio and the number of layers to control its optical characteristic. The optical characteristic of MD LB films was evaluated by UV spectroscopy and their surface morphologies were also observed using atomic force microscope. The optical characteristics of MD LB film were controlled by mixing ratio and LB layer deposited, which includes the potential control of the performance of photo-electric devices. The optical characteristic and surface morphology were also observed when MD LB films were modified using UV irradiation or heat treatment. As a result, we obtained the quantitative optical characteristic by controlling the mixing ratio with archidic acid and LB layer deposited. Also, the mixing ratio dependent surface morphology was observed. The experimental results strongly suggest that high efficient photo-electric devices can be obtained by LB method and modified by second treatment such as UV irradiation, heat treatment, and nano-lithography.

Optical properties and transmission features of J-aggregate in the merocyanine dye LB films by SNOAM

Abstract The changes of the absorption spectra by UV irradiation were measured with the optical spectrum of the J -band and the monomer band. We illustrated the topographical structure and optical structure of the merocyanine dye Langmuir–Blodgett (LB) films obtained by the scanning near-field optical/atomic force microscopy. The topographic image of the mutually mixed LB films shows more rough surface structure than expected and grains with average size of about 50 nm. In the optical transmission image, the elevated area means higher transmission than lower parts. In the continuous measurement of these dyes and the mutually mixed films, the appearance of near-field optical transmission images showed a certain dependence on the kinds of dyes with the shift and increase of transmission and the mutual mixing ratios of dyes. These experimental results suggest that there is a certain kind of interaction between these two dyes.

Optical Behavior of Thickness Shear Mode Quartz Crystal Resonator

In this study, we fabricated the optical system of merocyanine dye (MD) using the Langmuir-Blodgett (LB) method with various mixing ratios and numbers of layers to control its optical characteristics. We used quartz crystal microbalance (QCM) measurements and UV-visible spectroscopy to monitor and analyze the adsorption process of MD LB film. Aggregates, J form, were detected in MD LB film by UV-visible spectroscopy. The thermal relaxation kinetics for MD LB film was also investigated using UV-visible spectroscopy and the QCM. The thermal relaxation of MD LB film affected the vibration model of QCM and produced a resonant frequency shift. This strongly suggests that QCM technology has potential application in understanding the optical processing of MD LB films.

The Study on Optical Characteristics and Surface Morphologies for J-aggregates Formation of Merocyanine Dye LB Films

In this study, we investigated the optical characteristics of merocyanine dye Langmuir-Blodgett (LB) film and had analysis combined with surface morphology using AFM. And preparation condition for merocyanine dye LB film was determined. As a result, domains could be observed in the J-aggregate LB film and domain size was dependent on the mixing ratio. And the domain had very homogeneous two-dimensional structure. After UV irradiation, the domain size was decreased or disappeared correspond to the decrease of absorbance peak, which mean the dissociation of J-aggregate. These results can suggest the modulation of structure by light

Monolayer flow and in-plane orientation induced by a rotating disk in Langmuir and Langmuir-Blodgett films of a merocyanine dye

We have demonstrated that the rotating-disk method, which was proposed by Mingotaud et al. [J. Phys. Chem. 99, 17 068 (1995)] recently, is effective to induce in-plane orientation in the Langmuir-Blodgett films of merocyanine dye--behenic acid mixtures. To clarify the orientation mechanism, the monolayer flow due to the disk has been observed directly and interpreted by an analytical model incorporating a non-Newtonian behavior of the films. Based on this observation, a steady-state orientation-distribution function has been calculated. The comparison of the calculated orientation-distribution function and the experimental data shows that our model gives a guideline of the rotating-disk method.

Transient photoelectric responses in C60 LB films

Transient photoelectric responses in Schottky-type photoelectric cells with a photoconductive layer made of C60 arachidic acid mixed Langmuir-Blodgett (LB) film were examined to investigate the effects of symmetry and orientation of the molecules in the LB films for conduction process of photocarriers. Unlike merocyanine dye LB films, C60 LB films did not show a dispersive conduction, but only a highspeed response with a time constant of nanoseconds or less. These results suggest that symmetry and orientation of molecules play an important role in the response.

Characterization of Langmuir—Blodgett films using electron spin resonance spectroscopy

The role of electron spin resonance (ESR) spectroscopy in the characterization of Langmuir—Blodgett (LB) films is discussed. Early examples of the application of ESR spectroscopy in LB films are the studies of the structural and magnetic properties of fatty acid LB films containing metallic ions such as Cu 2+ and Mn 2+ and those of photoinduced electron-transfer processes in films containing donor and acceptor monolayers. In recent years, many varieties of molecules have been incorporated into LB films to develop films having new functions related to optical, electrical and other properties. LB films have also been employed as model systems for the study of the basic properties of molecular aggregates. As a result, there are increasing numbers of cases where the ESR technique has played a major role in elucidating the microscopic properties of these new LB films. Three cases are discussed here as illustrative examples. The first topic is the analysis of the in-plane anisotropy of the ESR spectra of the stable radical in merocyanine dye LB films, from which a flow orientation of the dye aggregates has been suggested as the origin of the in-plane anisotropy often observed in LB films. The hyperfine coupling due to a nitrogen in the dye molecule has been identified. The second case introduces the studies of conducting LB films composed of charge-transfer complexes. ESR can provide direct evidence for the formation of the conducting columnar structures of the constituent molecules through the temperature-dependent spin susceptibilities, which show the characteristics of low-dimensional metals or magnetic systems associated with structural disorder. In some systems, the molecular orientation and the magnetic interactions of quasi-one-dimensional spin chains have been deduced from the analysis of the spectral line shapes. The third case refers to LB films containing paramagnetic metallic ions, which still represent an important class of materials. The metallic ions act as well-localized probes in revealing the local orientation of molecules, the aggregation structure of molecules (such as dimer formation) and so on. Most of the research so far has been based on the standard continuous-wave ESR technique. A few works have been reported using the more advanced techniques of ESR, such as ENDOR (electron nuclear double resonance) and ESE (electron spin echo). These techniques, as well as others, are expected to extend the area of ESR application in the studies of LB films.

Preparation of merocyanine-dye Langmuir-Blodgett films and some of their physicochemical properties

We have developed a group of photo-active and/or surface-active stable merocyanine dyes as a promising candidate for a so-called biomimetic photosynthetic pigment. The dye surfactant molecules have been found to form Langmuir-Blodgett (LB) films where the molecules constitute J-aggregates. The dye, in aqueous organic solutions as well as in vacuum-evaporated films, have been studied by absorption and by fluorescence spectroscopy to gain insight into the physicochemical properties of the merocyanine-dye LB films on various solid substrates. In addition, the LB films of the dye with an octadecyl group have been studied by photoelectrochemical and electron spin resonance techniques. It has been found that the dye monolayer-deposited SnO 2 optically transparent electrodes tend to act as photocathodes. The behaviour of the photo-induced electron spin resonance signal is also reported.