Self-cross-linkable ferrocenyl-containing polysiloxanes as flexible electrochromic materials

Abstract

Flexible ferrocenyl-containing silicone rubbers (FSRs) with various ferrocenyl-substituted unit contents of 25, 50, and 75 mol% were obtained by applying a simple method included catalytic hydrosilylation (between polymethylhydrosiloxane and vinylferrocene) and self-cross-linking reactions (dehydrocoupling between Si–H groups). Self-cross-linking is one of the most suitable and simple methods to coat and obtain FSRs on various contact conductive surfaces, such as onto indium tin oxide (ITO) glass or ITO-poly(ethylene terephthalate). The synthesized FSRs exhibit the electrochromic (EC) properties, resulting from the reduction-oxidation of ferrocenyl groups (Fc/Fc+ transformations at E0 c.a. 0.36 V) and leading to color change: oxidation causes new band formation at 634 nm in ultraviolet-visible spectra. FSRs with ferrocenyl-substituted unit content of 50 mol% (FSR50) is the most optimal in terms of EC (coloration efficiency of 10.98 cm2/C, coloring and bleaching times of c.a. 49 and 66 s, which are close to undoped oligoaniline-functionalized polysiloxanes and carbazolyl-modified polysiloxanes) and mechanical properties (the tensile strength, Young's modulus, and elongation at break are 2.80 MPa, 25.33 MPa, and c.a. 50%, respectively). The previously reported EC polysiloxanes have lack of mechanical characteristics. Both electrochromism and flexibility predominantly make FSR50 promising materials for the creation of flexible and stretchable EC devices.