Amphiphilic Merocyanine Dye Research Articles

Crystallographic coherent lengths of J-aggregates and their absorption spectra

The Langmuir (L) and Langmuir–Blodgett (LB) films of the J-aggregates formed by amphiphilic merocyanine dye (MD) differ their absorption bands (J-bands), and the J-band in the LB film is located in shorter wavelength than that in the L film. From the grazing incidence X-ray diffraction patterns, the lattice structures and the crystallographic coherent lengths of the MD J-aggregates in the L and LB films were evaluated. Besides a 7% shrinkage of the 2-dimensional lattice in the LB film, more than two-order of magnitude shorter coherent lengths were observed in the LB film, suggesting that the difference of the J-band wavelength was attributed to the size effect of the J-aggregate crystal.

X-ray analysis on the size and shape of J-aggregates formed at the air-water interface

The X-ray analysis on the J-aggregate monolayer formed by amphiphilic merocyanine dye (MD) molecules at the air-water interface was carried out. For the analysis, a grazing incidence X-ray diffraction method was applied by using monochromatic synchrotron radiation. After deconvolution of the instrumental broadening factor from the obtained diffraction peaks, the pure widths of the diffraction peaks were substituted for the Scherrer formula, and the size and shape of the MD J-aggregate were evaluated. It was found that the MD J-aggregate had oval or elliptical shape with the long axis of submicrometer.

Structural Analysis of a J-aggregate Monolayer at the Air-water Interface by a Grazing Incidence X-ray Diffraction Method and Calculation of the Energy Level of Its Excitonic Absorption Band

The monolayer of amphiphilic merocyanine dye (MD) molecules at the air-water interface was observed by the grazing incidence X-ray diffraction (GIXD) method. At the air-water interface, the MD molecules formed two-dimensional crystallites (J-aggregates), whose excitonic absorption bands were located at longer wavelength than the monomer band. The structural analysis on the MD J-aggregate was carried out, and, using the determined structure, the relationship between the molecular arrangement and the energy shift of the visible absorption band upon crystallization was clarified. For the calculation of the energy shift, simple formulas were derived on the basis of molecular exciton theory. It was revealed that not only the transition dipole moment interaction but also the electric dipole moment interaction among the molecules plays an important role in the energy shift.

J-aggregate to J-aggregate relaxations in langmuir films of amphiphilic merocyanine dye derivatives studied by optimum difference spectrum method

Langmuir (L) films of amphiphilic merocyanine dye derivatives (DS and DSe) mixed with arachidic acid have been prepared on a Mg 2+-containing aqueous subphase. Time evolution of the molar absorption coefficient ( ɛ) spectra observed for them has shown that J-aggregates with relatively large red shifts (ca. 2800 cm −1) are the majorities at the initial stage, but J-aggregates with smaller shifts (ca. 2400 cm −1) become major within few minutes of compression. Isosbestic points clearly seen in the time evolution of the spectra imply those films include no other appreciable components. A similar phenomenon has been observed for DS films on Ca 2+-containing subphase. The pure spectra of the initial and final J-aggregates have been extracted from the experimentally obtained ɛ spectra by employing the optimum difference spectrum (ODS) method. Semi-quantitative discussion based on the extracted pure spectra has suggested that the observed phenomena are structural relaxations, i.e., changes in the molecular arrangements in the J-aggregates, and that the interactions between the static dipoles born by the dye molecules are not the main driving force of the J-aggregation of DS and DSe.

Formation of two-dimensional herringbone aggregates in Langmuir films of amphiphilic merocyanine dye derivatives

Doublet absorption bands are seen in visible spectra of Langmuir films of amphiphilic merocyanine dyes, DS, DO and DSe, prepared on pure water. In the DS and DO cases, the both maxima of the doublet bands exhibit red shifts upon the compression of the films. These phenomena cannot be explained by assuming that isolated monomers and/or dimers are the majority in the films. Contrastively, they can be well explained by assuming that large herringbone aggregates are the majority. In the latter model, the surface pressure-induced spectral change is interpreted as a structural phase transition. A numerical simulation for herringbone aggregates of DS reproduces the observed excitation wavenumbers. Infrared absorption spectra have been observed for Langmuir–Blodgett films of the dyes transferred from pure-water surfaces. They indicate the formation of mutual hydrogen bonds between the carboxylic groups in adjacent dye molecules and then suggest that the interaction between those groups is a part of the driving force of the aggregation.

Spectroscopic study of J aggregates of amphiphilic merocyanine dyes formed in their pure Langmuir films.

It is known that an amphiphilic merocyanine dye, 3-carboxymethyl-5-[2-(3-octadecyl-2(3H)- benzothiazolylidene)ethylidene]-2-thioxo-4-thiazolidinone (DS) and its derivatives DSe and 6MeDS form J aggregates under the presence of metallic cations, although the dyes' static dipole moments must be favorable for H aggregates. A metal-free J aggregate of 6MeDS has been generated in its pure Langmuir films and transferred onto CaF2 substrates to investigate the molecular environment around the carboxylic group born by the dye. Combining visible and infrared spectroscopy, geometrical consideration based on ab initio calculations, and simulation of the excitation energy, a structural model of this J aggregate has been proposed. With this model, formation of intermolecular carboxyl-keto hydrogen bonds, which can compensate the electrostatic disadvantage of the J aggregate under the presence of water, has been suggested. As for another derivative of DS, DO, similar discussion has been made for its Mg2+ -containing J aggregate, which is found in this work. In addition, the proposed structural model can tell the cause of the difference in the tendency to J aggregate among 6MeDS, DSe, DS, and DO.

Preparation of J-Aggregate Liposome Dispersions and Their Chromic Transformation

We report the preparation of aqueous liposome dispersions of J-aggregates formed by the amphiphilic merocyanine dye (MD). A series of liposome-forming lipids were dispersed together with MD J-aggregates at different molar ratios of MD to lipid. The MD J-aggregate dispersions prepared with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at the MD to DMPC ratio of 0.16 exhibit good dispersibility; that is, they can be readily redispersed without any flocculation even after their precipitation. By use of different counterions for the MD molecules, two types of J-aggregate dispersions, one that exhibits an absorption band (J-band) at 635 nm (type I) and the other at 600 nm (type II), were obtained. As an example of the use of MD J-aggregates liposome dispersions, the thermochromic transformation of MD J-aggregates was demonstrated. When the dispersions are heated, J-aggregates of type I transformed into type II at a certain temperature (T(disp)). The parameters that control the speed of the transformation and the value of T(disp) were determined.

FT-IR study of Langmuir–Blodgett films of a merocyanine dye: effect of 13C-substitution and influence of J-aggregation

Abstract An amphiphilic merocyanine dye, C 18 DS, forms J-aggregates in its Langmuir–Blodgett (LB) films. In order to investigate the influence of the J-aggregation upon the electronic state of the dye, IR absorption spectra were observed for LB films of 13 C-substituted C 18 DS, in which a carbon atom in the central conjugated system of the dye is replaced by 13 C. Clear red shifts due to the 13 C-substitution were observed for the IR bands that exhibit red shifts upon the J-aggregation. This result shows that these bands originate from stretching of central conjugated system, and then suggest an enhancement of the intramolecular charge transfer upon the J-aggregation. Frequency calculation using the density functional method was performed for C 4 DS, in which the octadecyl group of C 18 DS is truncated to a butyl group. The calculation results coincide with both the IR spectrum of C 18 DS and the 13 C-substitution effect on it. The observed IR bands were assigned on the basis of this calculation.

Fatty Acid May Assist Nucleation of J-Aggregates in Mixed Langmuir Films of an Amphiphilic Merocyanine Dye Prepared on a Pure-Water Subphase

Langmuir films of 1:x (x≤1) mixtures of an amphiphilic merocyanine dye (DSe) and a fatty acid prepared at an air–pure water interface were characterized by in-situ observation of their visible absorption spectra. A distinct J-band was observed at low surface pressures even with x≪1. The time and x dependence of the absorption spectra indicate that the fatty acid assists the nucleation of the J-aggregates and that one J-aggregate can contain 102 DSe molecules. In addition, a surface pressure-induced phase transition was detected, suggesting that, in these Langmuir films, J-aggregated DSe requires a larger area than non-J-aggregated DSe.

Phase transition between different J-aggregate states of amphiphilic merocyanine dye molecules

The two-dimensional phase transition between different J-aggregate states in the amphiphilic merocyanine dye monolayer was investigated using a multi-purpose nonlinear optical microscope. Precise in-situ observations of the transition on cooling revealed the nucleation and growth process of the low temperature phase in the matrix of high temperature phase.

Structural Phase Transition in Two-Dimensional Polar Crystallites of Organic Dye Molecules: In-Plane X-ray Diffraction Analysis

The two-dimensional polar crystallite of amphiphilic merocyanine dye molecules exhibits a thermochromic phase transition on the aqueous subphase. Grazing incident X-ray diffraction measurements were performed onto Langmuir-Blodgett films consisting of the high and/or low temperature phases of the crystallites. It was clarified that the transition accompanies the structural change of the crystallite.

Structural Phase Transition in Two-Dimensional Polar Crystallites of Organic Dye Molecules: In-Plane X-ray Diffraction Analysis

The two-dimensional polar crystallite of amphiphilic merocyanine dye molecules exhibits a thermochromic phase transition on the aqueous subphase. Grazing incident X-ray diffraction measurements were performed onto Langmuir-Blodgett films consisting of the high and/or low temperature phases of the crystallites. It was clarified that the transition accompanies the structural change of the crystallite.

Structural phase transition of merocyanine J-aggregate induced by ion-recombination in the aqueous sub-phase

By using the sub-phase, which contains two different kinds of counter-ions, we found a reversible thermochromic transition between different J-aggregate states of amphiphilic merocyanine dye (MD) molecules in the monolayer at the air–water interface. This chromatic change is attributed to the structural phase transition of MD J-aggregate crystallites induced by the mutual recombination of different counter-ions to MD molecules. The drastic morphological change of the MD monolayer during the transition is revealed by the in-situ observation using a multipurpose non-linear optical microscope.

Reversible Thermochromic Transition between Different J-Aggregate States of Amphiphilic Merocyanine Dye Crystallites

Reversible Thermochromic Transition between Different J-Aggregate States of Amphiphilic Merocyanine Dye Crystallites

Reversible Thermochromic Transition between Different J-Aggregate States of Amphiphilic Merocyanine Dye Crystallites

ABSTRACTOn the subphase, which contains Cd2+ and Mg2+ ions, two-dimensional (2D) J-aggregate crystallites of merocyanine dye molecules exhibit a thermochromic transition. The J-aggregate absorption band of the low (LT) and high temperature (HT) phases are located at 620 and 595 nm, respectively. In order to clarify the in-plane structure of the 2D J-aggregate crystallites, grazing incident X-ray diffraction measurements were performed on the Langmuir-Blodgett multi-layers which consisted of the monolayers of LT and HT phases. It was revealed that the in-plane arrangement of the dye molecules is slightly different in the J-aggregate crystallites of LT and HT phases.

Brickstone arrangement in J-aggregates on an amphiphilic merocyanine dye

J-aggregates formed in monolayers of an amphiphilic merocyanine dye were transferred onto solid supports and were investigated by scanning force microscopy (SFM). Islands of bulk phase deposited material were observed after the monofilm transfer onto mica. The islands are up to several μm 2 in area and several nm height. On these islands molecular resolution was achieved in the SFM. The dye molecules are arranged in a rectangular unit cell. The unit cell area was in agreement with data from surface pressure—area isotherms and with the dimensions of the dye molecule. Our SFM data were consistent with a brickstone arrangement of dye molecules in the J-aggregates.

Spectroscopic characteristics of an amphiphilic merocyanine dye: A probe of polarity in micelles

The amphiphilic merocyanine dye C 16M was synthesized and its absorption spectra were investigated in organic solvents of varying polarities and solutions of different pH. The spectral behaviour was also studied in aqueous and in reversed micelles of two differently charged detergents, CDBA (cetyldimethylbenzylammonium chloride) and AOT (sodium bis 2-ethylhexyl sulfosuccinate). The results show that the p K a value of C 16M is more acidic by four p K a units in aqueous micelles than that in methanolic buffer solutions. The spectral changes observed in methanol/H 2O mixtures are indicative of self-aggregation of C 16M forming micelles. It was found that this molecule exhibits an extreme negative solvatochromic effect, which permits its use as a chemical probe to monitor the polarity of aqueous micellar systems as well as the polarity of the water pools in reversed micelles.