Dft Study of the Structural and Electronic Properties of Conducting Oligo(p-Fluorophenylthiophene)

A comprehensive theoretical study on the conducting oligomeric systems is carried out in view of their potential application in electrochemical charge storage. Density functional theory (DFT) calculations are carried out on a series of oligomers made up of 3-(p-fluorophenyl)-thiophene (FPT) to estimate the geometric and electronic structures, conjugated lengths, bandwidths, and energetic properties of polymeric systems. The calculations are performed on the dimer up to octamer chains in the ground state and both pand n-doped phases. The results obtained show that the conjugated system in p- and n-doped oligo(FPT)s has a higher distance with more planar chains with respect to their neutral forms. The band gap energy between the frontier molecular orbitals decreases dramatically for both ionic states, and approaches a low limiting value with increasing oligomer length. The charge delocalization through the monomer rings along the backbone oligo(FPT)s reveals that the p- and n-doped states had more suitable properties, reflecting the electron and hole transport characteristics for conductivity, respectively. The calculated first excitation energies for oligo(FPT)s at the time-dependent B3LYP/6-31G(d,p) level of theory indicate that both doped oligomers have lower excitation energies, which display a red shift in their absorption spectra. For polymeric systems, the evolution of ionization potential, electron affinity, electron chemical potential, molecular hardness, and thermodynamic stability is made through the extrapolated oligomer ones.