When cyanine dye with long chain hydrocarbon octadecane form mono-layer at air-water interface

the long axes of chromcphore all lie in the layer while the short axes stand perpendicular to it.Under certain pressure

the long axes of near neighbors are usually parallel and closely to some extent forming a strure so called J-aggregates.The structure cf J-aggregates is such that the dipole of the dye can coupled together so the molecular exciton theory of Davydov for weakly coupled composite systems can be used.According to this theory

the energy transfer in such systems is the rapid

long range exciton transfer.To study the energy transfer inside the Langmuir-Blodgett monolayer

we prepare the monolayer by standard L-B technique

i.e.

mixing proper molar ratio of dye Ⅰ and dye Ⅰ and adding sufficient quantity of hexadecane so that dye 1+dye Ⅱ: hexadecane=1:1. The fluorescence spectrum of dye I and the absorption spectrum of dye Ⅱ overlap partially

providing the possibility for energy transfer from excited dye Ⅰ to dye Ⅱ. It is well known

that there are various types cf energy transfer between molecules.In our case

Forster transfer and exciton transfer are considered.