Rapid dissociation of merocyanine dye aggregates by reduced pressure in mixed Langmuir-Blodgett films

Abstract

We have examined the influence of reduced pressure on the redshifted and the blueshifted aggregates formed in the mixed Langmuir-Blodgett (LB) films of the merocyanine dye–arachidic acid (MS–C20) binary and the MS–C20–n-octadecane (MS-C20-AL18) ternary systems with the molar mixing ratios of [MS]:[C20]:[AL18]=1:2:x in the range of 0≦x≦5.0. The peak of the redshifted band at 590nm in the binary system remains constant before and after the reduced pressure treatments. On the other hand, not only the peaks of the blueshifted bands at 505nm and 520nm but also the redshifted shoulder at around 580nm in the ternary systems drastically diminishes after the treatments, indicating the dissociation of the MS aggregates. The long axis of AL18 molecules with the all-trans conformation, which tends to fill the MS empty spaces, is aligned along the stacking direction of the mixed LB films before the treatments, whereas almost all the AL18 molecules are absent after the treatments. Therefore, the dissociation is considered to be ascribed to the removal of the AL18 molecules with the uniaxial orientation in the mixed LB films by reduced pressure, leading to a change in the MS aggregation state.

Conversion of the Aggregation State of Merocyanine Dye, Modification of the Subcell Packing of Arachidic Acid, and Removal of the Majority of n-Octadecane by Hydrothermal Treatment in the Liquid Phase in a Mixed Langmuir−Blodgett Film of the Ternary System

“…We have been engaged in research on the control of dye aggregation states by using mixed Langmuir−Blodgett (LB) films with merocyanine dye having an octadecyl group ( n = 18, MS 18 , 3-carboxymethyl-5-[2-(3-octadecylbenzothiazolin-2-ylidene)ethylidene]rhodanine; see Figure ). In a mixed LB film composed of an MS 18 −arachidic acid (C 20 ) binary system, a sharp, red-shifted J-band with an absorption maximum at 590 nm is formed, which is markedly shifted to a lower-energy side from the MS 18 monomer peak near 530 nm when it is prepared under an aqueous subphase containing a cadmium (Cd 2+ ) ion. − In addition, a blue-shifted band appears at 505 nm by adding a small amount of n -octadecane (AL 18 ) to the above MS 18 −C 20 binary system. − We assigned the 505 nm band to the H-band on the basis of the shift to the higher-energy side, sharpness, and in-plane anisotropy of the band. − …”

Structural Characterization of a Mixed Langmuir−Blodgett Film of a Merocyanine Dye Derivative−Deuterated Arachidic Acid Binary System and the Influence of Successive Hydrothermal Treatment in the Liquid Phase on the Film as Investigated by Polarized UV−Visible and IR Absorption Spectroscopy

“…The concentration of CdCl 2 and NaHCO 3 mixed was the same as that reported previously. [12][13][14][15][16][17][18][19][20] The subphase was kept at 20 °C during surface pressure (π)-area (A) isotherm measurement and film deposition. The π-A isotherm measurement of monolayers was performed at a compression rate of 0.0500 {Å 2 /(molecule • sec)}.…”

“…The MO 18 concentration was on the order of 10 −4 M. An aqueous subphase containing cadmium chloride (CdCl 2 ) and sodium hydrogencarbonate (NaHCO 3 ) was prepared using ultrapure water with a resistance of 1.82 MΩ·cm, and a TOC level of 1 ppb at 20 °C (Purelab Ultra, Analytic, Organo Co. Ltd., Tokyo, Japan). The concentration of CdCl 2 and NaHCO 3 mixed was the same as that reported previously. − The subphase was kept at 20 °C during surface pressure (π)−area ( A ) isotherm measurement and film deposition. The π− A isotherm measurement of monolayers was performed at a compression rate of 0.0500 {Å 2 /(molecule·sec)}.…”

“…[1][2][3][4][5][6][7][8][9][10][11] Because the J and H aggregates can be easily controlled in Langmuir-Blodgett (LB) films containing merocyanine dye (see Figure 1A; MS 18 , X ) S, 3-carboxymethyl-5-[2-(3-octadecylbenzothiazolin-2-ylidene)ethylidene]rhodanine), we have been using LB films containing MS 18 to investigate the abovedescribed topics. [12][13][14][15][16][17][18][19][20] The formation mechanisms of the J and H aggregates of MS 18 have been revealed by Ikegami et al [21][22][23] and our group, 19 respectively. On the other hand, when the LB film of an analogous merocyanine dye (see Figure 1A; MO 18 , X ) O) and arachidic acid (C 20 ) binary or pure MO 18 system is prepared under an aqueous subphase containing a cadmium ion, it is well-known that the absorption band with a maximum near 505 nm, which is broader in shape than the MS 18 J and H bands, is formed.…”

“…The formation of dye aggregates based on self-organized molecular nanostructures, control of chromophore arrangements in the dye aggregates, and elucidation of the aggregation mechanism in ultrathin films have been the subjects of significant research aimed at enhancing the higher performance of photovoltaic cells, optical waveguides, and ultrafast optical switches that include such dye-containing ultrathin films. − Because the J and H aggregates can be easily controlled in Langmuir−Blodgett (LB) films containing merocyanine dye (see Figure A; MS 18 , X = S, 3-carboxymethyl-5-[2-(3-octadecylbenzothiazolin-2-ylidene)ethylidene]rhodanine), − we have been using LB films containing MS 18 to investigate the above-described topics. − The formation mechanisms of the J and H aggregates of MS 18 have been revealed by Ikegami et al − and our group, respectively. On the other hand, when the LB film of an analogous merocyanine dye (see Figure A; MO 18 , X = O) and arachidic acid (C 20 ) binary or pure MO 18 system is prepared under an aqueous subphase containing a cadmium ion, it is well-known that the absorption band with a maximum near 505 nm, which is broader in shape than the MS 18 J and H bands, is formed. − This 505 nm band of MO 18 has been ascribed to the monomer , or a non-J aggregation. − …”