The investigation of acid effect on chemical polymerization of indole

The present study investigates the effects of Lewis acid and protonic acid on the chemical polymerization of indole using electrical conductivity measurements and nuclear magnetic resonance, UV–visible, and Fourier transform infrared spectroscopy techniques. These effects are explained by theoretical calculations on the basis of molecular mechanic (MM+) and semi-empirical Austin Model 1 methods. As a result, it has been shown that indole interacts with proton and Lewis acids by the way of different mechanisms. Theoretical research has demonstrated that while BF₃, a Lewis acid, adds to the N atom in the indole, which has a basic character due to its lone-pair electrons, proton, H⁺ adds to the indole ring on C₃ atom. These additions affect both the polymerization of indole and the conductivity of polyindole. Polyindole conductivity is increased by BF₃ addition and decreased by H⁺ addition.