J-aggregates of thiacyanine dye organized in LB films: Effect of irradiation of light

In the present communication we report the preparation and characterizations of Langmuir and Langmuir–Blodgett films of a thiacyanine dye N,N′-dioctadecyl thiacyanine perchlorate (NK) mixed with Octadecyl trimethyl ammonium bromide (OTAB). The relationship between the molar ratio of OTAB and NK and the orientation of molecules at the air–water interface was investigated using surface pressure-area per molecule (π–A) isotherm. UV–vis absorption and fluorescence spectroscopic investigations reveal that prominent J-aggregation of NK molecule was observed in the LB films lifted at higher surface pressure. This J-aggregation can be controlled by diluting the NK molecules with OTAB. It was observed that the J-aggregates of NK decayed to monomer and H-aggregates when the NK-LB film was exposed to a monochromatic light of wavelength 460 nm (λmax of J-aggregates).