Ultrafast photoresponsive materials and molecular photonics applications by guided wave mode geometry

Molecular photonics, information processing based on strong interactions of photons and molecules, has attracted much attention, since it can fully utilize many superior properties of both photons and molecules. We have developed polymeric materials showing ultrafast absorption changes in the visible to near-infrared regions including the telecommunication wavelength by photoinduced electron transfer and reverse reactions between substituted pyridinium and its counter anion. By selecting the counter anion we succeeded in making steady and ultrafast absorption changes. Time-resolved absorption and fluorescence spectroscopy upon femtosecond laser excitation revealed reaction mechanism and ultrafast dynamics. In order to fully utilize such photoresponses in molecular photonics, we proposed guided wave mode (GWM) device composed of a prism, a low refractive index polymer film, and a photoresponsive polymer film. The reflectance in this GWM is controlled by many factors such as thickness values and complex refractive indices of two polymer layers as well as an incident angle and wavelength. We successfully achieved sensitive, all optical, and very fast control of reflectance by means of photoinduced complex refractive index changes upon femtosecond laser excitation.