Characterization of hemicyanine Langmuir-Blodgett films by picosecond time-resolved fluorescence

Hemicyanine Langmuir-Blodgett films have been elaborated and characterized using stationary and time-resolved spectroscopic techniques. Depending on the experimental conditions, especially the pH of the water subphase, the absorption spectra of the films indicate the presence of non-fluorescent H-aggregates in the monolayer. Time-resolved fluorescence measurements revealed three mono-exponential decay times: a very short one (20-23 ps) attributed to an excited intramolecular charge transfer state and two longer ones (100-120 ps and 400-590 ps) attributed to the photoisomerization of the chromophores.