A Benchmark Study on the Properties of Unsubstituted and Some Substituted Polypyrroles

Collins U Ibeji

doi:10.4172/2161-0398.1000193

Abstract

The geometric, thermodynamic, electronic and absorption properties of Pyrrole and some of its derivatives have been carried out using CCSD/6-311++G(d,p)/STO-3G, TD-DFT and DFT/B3LYP/6-31G(d) from monomer to five repeating units. Substitution by a methyl group at C3 and functional groups at C4 cause small changes in atomic distances. The estimated inter-ring bond length based on Badger's rule of 1.41 A indicates that the average structure is about 30% quinoid. The geometries indicates that strong conjugate effects and effective aromatic structure are formed in the order Pyrrole>MPCam>MPC. The oligomers of simulated compounds have been extrapolated to polymer through second-degree polynomial-fit equation with r2 value ranging from 0.96-0.99. Calculated band gap of pyrrole, which is 2.9 eV, significantly correlates with the experimental value which ranges from 2.9-3.2 eV and this corresponds to π-π* transition energies. Natural bond orbitals of polypyrrole reveals that the wavefunctions contain dynamic correlations (single reference), closed shell character while substituted polypyrrole are multireference (static correlation), open shell character.

Highlights

The applications of conducting polymers have been extensively studied over the years due totheir electronic, electrochemical and optical properties
We have designated the two orbitals with occupancies closest to 1 the highest occupied natural orbital HONO with occupancy greater than 1 and lowest unoccupied natural orbital LUNO with occupancy less than 1, respectively. These natural orbitals together with usual highest occupied molecular orbital Highest Occupied Molecular Orbital (HOMO) and lowest unoccupied molecular orbital Lowest Unoccupied Molecular Orbital (LUMO) are shown in Figure 7 The result shows that poly pyrrole is a single reference(dynamic correlation), closed shell system while other studied systems are multireference, open shell in nature
The mutual comparison of the obtained equilibrium geometries showed that the Density Functional Theory (DFT) predicted C-C and C=C bond length are in agreement with the experimental values

Summary

Introduction

The applications of conducting polymers have been extensively studied over the years due totheir electronic, electrochemical and optical properties. T1 diagnostics and Natural bond orbital coupled cluster tool calculation have been carried out These methods are useful and reasonably accurate tools for the exploration of the spectroscopic and geometric properties of conjugated polymers. The geometric properties studied at ground state were selected bond length, bond angle, dihedral angle (torsional angle) and the intermolecular charge transfer (ICT) These were determined using restricted hybrid Density Functional Theory (DFT) method at B3LYP/6-31G*. Thermodynamic properties considered in this study include: Calculated energies (E0) Zero Point Energy (ZPE), Enthalpy of formation (∆Hof), Entropy (∆S) and Heat of formation (∆Hfo) These have been determined using restricted hybrid Density Functional. For UV−VIS calculations, TDDFT calculations have been performed at B3LYP/6-31G*

Findings

Result and Discussion

Conclusion