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-aggrega te states of amphiphilic merocyanine dye (MD) molecules in the monolayer at the air-water interface. This chromatic change is attributed to the struct ural phase transition of MD J-aggregate crystallites induced by the mutual recombination of different counter-ions to MD molecules. The drastic morpho logical change of the MD monolayer during the transition is revealed by the in-situ observation using a multipurpose non-linear optical microscope. (C ) 2000 Published by Elsevier Science B.V.