We report the optical properties of the cyanine dye molecule thin film fabricated by a layer-by-layer method. While the absorbance and the film thickness increase with the dipping time, the use of a multilayer structure enables fabrication of the thin film without the creation of the molecule bundle that suppresses light scattering and the large absorbance obtained for the shorter dipping time. Exciton dynamics are studied by using a pump-probe technique; the signal shows two decay components in the multilayer sample that originates from the fast intramolecular relaxation and from the slow exciton relaxation. The temporal profiles show at the high signal-to-noise ratio. These results indicate that the thin film without the creation of the molecule bundle fabricated by the layer-by-layer method can be used for ultrafast all-optical switches.

Increase in exciton decay rate due to planeto-plane interaction between cyanine thin filmsWe report an increase in exciton decay rates because of long-range interaction based on surface charge between cyanine thin films. The dependence of the decay rate on the spatial separation between the cyanine molecule layers shows that the rate is almost constant, which is different from the well-known energy transfer process. The rate is hardly affected by the fluctuation of the film thickness,

Exciton decay dynamics can be optically controlled by changing the excitation conditions, particularly, the excitation intensity. In this study, we report how the exciton dynamics in cyanine thin films depend on the excitation intensity and sequence. The excitons in these films have two decay components, and the ratio of the population of the fast decay component to the total population depends on the excitation intensity. Conversely, sequential excitation by a second optical pulse does not alter this ratio. Although the total excitation power is comparable, the change in the dynamics by the second pulse is different from the simple increase in the excitation power. Therefore, the sequential excitation by the second pulse can be a key point for realizing low-power optical switches.