Reorganization of Redshifted Band in Merocyanine–Cd Arachidate Mixed Langmuir–Blodgett Films Induced by Hydrothermal Treatments

Abstract

The effect of hydrothermal treatments (HTT) on merocyanine (MS)–Cd arachidate mixed Langmuir–Blodgett (LB) films has been studied. At temperatures ranging from 30 to 90 °C, the redshifted J-band in the as-deposited state has been found to reorganize under the condition of 100% relative humidity, forming a new phase of further redshifted bands with spectra sharper than those of the as-deposited J-band. The HTT-induced phase closely resembles that induced by the heat treatment without humidity control, while the occurrence of the latter is limited to 60–70 °C. The water content introduced into the LB system during HTT is suggested to play a catalytic role in facilitating the reorganization by its lubricating and/or hydrolyzing effects to soften the film structure.

Thermal Stability of the Hydrothermally-induced J-band in Merocyanine-containing LB Films

“…The film, originally blue in color, turns red as a consequence. It has been previously reported that the in-plane anisotropy tends to decrease as the DHT process proceeds, with R decreasing down to approximately unity in the present case [10][11][12][13][14][15][16]. Figure 3 shows the <A> spectra successively taken on the same sample, where the thin solid, thick solid and dotted lines refer to the as deposited state, after HTT(60'C, 40 min) and after HTT(60'C, 40 min) ->DHT(llO'C, 270 min), respectively.…”

“…2. The A l l and A_~_ components of the as-deposited spectrum are associated with in-plane anisotropy with the dichroic ratio R=A 11 /A_~_ usually falling within a range of 1.2-2.5, depending on the deposition condition [8][9][10][11][12]. Three components are recognized as reported in previous papers [10,13,16]: two shoulders at A-~490 nm and 540 nm, respectively, and the J-band at A-~490 nm.…”

“…20 mm in diameter and 150 mm long) with a screw lid at one end was employed for both DHT and HTT. A small amount of pure water (2 cm 3 or less) was introduced into the tube to satisfy the condition of 100% humidity for HTT as described in previous papers [8][9][10][11][12][13][14][15][16]. A spacer was then put at the bottom to avoid direct contact between the sample and the water.…”

“…It has been reported that the J-band is dissociated by acid treatments (ATs) and dry-heat treatments (DHTs), and restored by basic treatments (BTs) [5,6]. Further, we have recently shown that the J-band is reorganized by hydrothermal treatments (HTTs) under condition of 100% humidity at a temperature range of 30 ~90°C to form a new phase of J-aggregate with spectra further redshifted and sharper in shape than that in the as-deposited state [8][9][10][11][12][13][14][15][16]. The photomicroscopic image, initially anisotropic and featureless, is changed by the application of HTT into isotropic and filled with round-shaped superstructures as large as up to ea.…”

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

“…The as-deposited J-band originally located around 590 nm is reorganized by HTT to form a new phase associated with a further narrowing and a red shift of the peak [16-26]. …”