Refractive index change of an amorphous bisbenzothienylethene

A bisbenzothieneylethene exhibiting a photochromic behavior in the amorphou s bulk solid state was synthesized. Upon alternate ultraviolet (UV) and vis ible light irradiation the amorphous thin film underwent a reversible color change and modulation of the refractive index. The refractive index chan-e was determined at 632.8 nm and 817 nm using a prism coupling method. The d ifference in the refractive index value between the open- and closed-ring i somers was as high as 0.064 at 817 nm.