New developments in photochromic materials showing large change in the refractive index

Organic photochromic materials have been studied as active materials in optical devices since they show a reversible change of color in the visible region and appreciable reversible changes of the refractive index (?n) in the NIR. The latter peculiar property can be suitably exploited for the realization of holographic optical elements (HOEs) and in particular volume phase holographic gratings (VPHGs). Photochromic polyester based on diarylethene alcohol was synthesized and characterized both in solution and in thin film. The optical properties of the films were good enough for making optical devices and the modulation of the refractive index (measured by spectral ellipsometry) was large at 1.5 micron and it became even larger at shorter wavelength where the material is still transparent. Such photochromic material is a good candidate for making rewritable efficient HOEs.