Interplay between Optical and Electronic Characteristics of Castor Oil-Derived Hybrid Polymers

Abstract

This work explores the correlation between information obtained from optical and electrochemical spectroscopy─specifically impedance-derived electrochemical capacitance spectroscopy (ECS)─applied to castor oil-derived hybrid polymers. The organic–inorganic hybrid polyurethane, called t-urethanesil_CO, was synthesized via a mild, catalyst-free sol–gel route and characterized by using FTIR spectroscopy, ²⁹Si nuclear magnetic resonance, and thermogravimetric analyses. ECS analysis provided unprecedented information about the electronic structure of t-urethanesil_CO through the chemical capacitance (C_q) response as a function of the applied potential, which is proportional to the experimental pseudocapacitive density of states (DOS). A Gaussian-shaped DOS profile was observed, characteristic of noncrystalline materials. Furthermore, light-assisted ECS─performed under continuous photoirradiation─revealed an enhancement in the C_q response, attributed to electron occupancy of excited states, consistent with the population of excited states under photoirradiation. To further investigate the optical-electronic interplay, the polymer was doped with photoactive polyoxometalate H₃PW₁₂O₄₀ (HPWA). The resulting PWA@t-urethanesil_CO exhibited potential shifts in the C_q profile and the emergence of new features under light-assisted ECS, indicating the formation of new electronic states within the polymer matrix arising from strong interactions with the dopant and their reduced specie W⁵⁺, respectively. These findings highlight light-assisted ECS as a powerful in situ probe of the electronic structure in optically active hybrid materials.