MEROCYANINE J AGGREGATES - FORMATION AND STRUCTURAL-CHANGE ON CHEMICAL AND THERMAL TREATMENTS

The effect of counterions of a merocyanine dye, 3-carboxymethyl-5[2-(3-octadecyl-2(3H)-benzoselenazolinylidene) ethylidene]-2-thioxo-4-thiazolidinone, on the formation of J aggregates was investigated with the monomolecular films on water and the Langmuir-Blodgett films. As the counterions, ammonia and various amines as well as some metal ions were employed. The dye formed J aggregates with $lambdmax at 620-630 nm on the subphase containing Co2+, ammonia and primary amines of small size such as methylamine, ethylamine and ethylenediamine. On the subphase containing Ba2+ and Ca2+, on the contrary, the dye formed J aggregates with λmax at 600 nm. A chelate structure in the rhodanine ring was assumed to play an important role in J aggregation. The J aggregates in the film transferred onto a solid substrate were destroyed thermally and restored on subsequent treatment with water vapour as well as with ammonia vapour. In-plane anisotropy of the dye orientation did not change on treatment with aqueous HCl vapour, while the anisotropy disappeared on thermal treatment. The thermal and chemical destruction of the J aggregates was found to be based on different mechanisms.