SOLVENT AND SUBSTITUENT EFFECTS ON ELECTROCHEMICAL PARAMETERS OF 5-MEMBERED HETERO AROMATIC MONOMERS: DENSITY FUNCTIONAL THEORY STUDY

Abstract

Pyrroles, thiophenes and furans represent building blocks conjugated poly(heterocycles) which, as organic conductors are potential materials for various applications. Oxidation of βsubstituted pyrroles, thiophenes and furans constitutes an important first step in the process of electroplymerization. Key electrochemical parameters such as function coefficient (Fn), atomic charge distribution, ionization potential (IP) and bandgap and salvation energy are most important properties regarding monomers and their radical cations. These properties are studied as a function of electron withdrawing and electron donating substituent of pyrrole, thiophene and furan ring and studied as a function of solvent polarity. Evaluation of electrical, structural and thermodynamic properties the monomers and their corresponding radical cations are studied as an effect on various electrochemical parameters using density functional theory (DFT) and B3LYP methods with 6-31G(d, p) and 6-31++G(d, p) basis set in solution phase using Polarized Continuum Model (PCM) method. The theoretical calculation indicates electron-withdrawing solvents increase the IP while electron-donating groups decrease the value and hence contributing for easer oxidation step. It was also observed that dipole moment, Fn, atomic charge distribution and bandgap follows generally the order pyrroles > furans > thiophenes. Besides, the results showed that charge distribution decrease with polarity of solvent and in the case of electron donating group whereas solvent polarity on Fn have no significant effect. On the other hand, bandgap of monomers are greater than their radical cations indicating the stability of the monomers. Generally, the DFT calculation demonstrates that efficiency of polymerization is affected with the nature of substituent and solvent polarity.