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.
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.
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