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

TL;DR

This study explores the formation and light-induced decay of J-aggregates in LB films of a thiacyanine dye mixed with OTAB, revealing controllable aggregation and photobleaching effects relevant for optical applications.

Contribution

It demonstrates the controlled formation of J-aggregates in LB films and their decay under monochromatic light, a novel insight into dye aggregation behavior in such films.

Findings

J-aggregates form at higher surface pressures in LB films.

Dilution with OTAB controls the extent of J-aggregation.

Exposure to 460 nm light causes decay of J-aggregates to monomers and H-aggregates.

Abstract

In the present communication we report the preparation and characterizations of Langmuir and Langmuir-Blodgett films of a thiacyanine dye-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 ({\pi}-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 (Lambda max of J - aggregates).