Aggregation and photoisomerization of amphiphilic crown-ether styryl dye in monolayers at the interface

The molecules of trans-isomer of styryl dye la, containing the benzo-18-crown-6 moiety and the methoxybenzothiazole residue with the N-octadecyl substituent, were shown to form stable, highly ordered monolayers at the water/air interface. Increasing the surface pressure of the monolayer results in the formation of the H-aggregated molecules of compound la. The H-aggregates tend to dissociate to the monomeric trans-form, when the monolayer forms in the Langmuir-Blodgett film (LB film). The light irradiation of the LB films leads to the partially reversible trans-cis-photoisomerization of compound la, whose efficiency is much lower than that observed in an acetonitrile solution of In. The aggregation of cis-la isomers in the LB film is suggested to hamper the reverse cis-trans-isomerization. The aggregation of trans-1a molecules in the LB films does not occur in air, but, after dipping in an aqueous solution, molecules of the LB film slowly form J-aggregates. A model of the structural organization of trans-la molecules in the LB films was proposed.