Morphology/potential-dependent electrochromic behaviour of poly(Hydroxyphenyl porphyrin) films

Abstract

Polymer films based on two different hydroxyphenyl porphyrins were obtained by the superoxide-assisted electrochemical method. Using atomic-force microscopy, we demonstrated the uniformity and low roughness of the films with a thickness of up to ∼200 nm. The spectral data obtained in this work confirm that the porphyrin moieties are preserved and connected via C-O-C bridges in the prepared materials. The spectral response of the films was studied in a wide range of potentials. It is shown that electrooxidation and electroreduction of 100–150-nm-thick 2H-5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin polymer films leads to significant and reversible spectral changes, which makes the films promising for electrochromic applications. The work also shows the limiting factors for the formation of electrochromic porphyrin-based polymers. We found that 2H-5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin films cracked if the film was over 230 nm thick and observed degradation of the 2H-5,10,15,20-tetrakis(m-hydroxyphenyl) porphyrin films at high potentials. In addition, the paper discusses the causes of spectral changes in the poly-hydroxyphenyl porphyrin films as well as their degradation phenomena.