Electrochromism of Metal-Free Phthalocyanine Langmuir-Blodgett Films

A metal-free phthalocyanine film was prepared by Langmuir-Blodgett (LB) technique. It was observed for the first time that the LB film deposited on a ITO/glass showed electrochromic color changes in aqueous solutions of KCl. The color of the film was changed from original blue-green to purple-red in an oxidation process, and to dark-purple in a reduction process. The color changes observed in the LB film were quite similar to those in lantanoid-diphthalocyanine evaporated films. On the contrary, the annealed LB film, of which the structure was dimeric-like, did not show any electrochromic color changes.