The spectroscopic behaviour of J-aggregates of cyanine dyes without long chains incorporated in the monolayer assemblies

Abstract

Cyanine dyes without long alkyl chains can be incorporated into composite monolayers with stearic acid at the air-water interface. In the composite monolayer of a 1:1 mixture of dye I (5,5′-dichloro-3,3′,9-triethylthiacarbocyanine chloride) and stearic acid on the water surface, two J-bands were observed, depending on the surface pressure. In the case of dye II (5,5′-dichloro-3,3′-diethyl-9-phehylthiacarbocyanine chloride) the J-aggregate was more stable than those of dye I. The composite monolayers including the dyes can be transferred onto a solid support, retaining the J-aggregate between stearic acid layers. When the temperature was raised above 55°C, the J-band decreased very rapidly with a simultaneous increase in dimer and monomer bands. These spectral changes can be repeated with good reversibility. The correlation between the absorption spectra and the formation of J-aggregates for dyes I and II is discussed.