Time-dependent density functional theory studies on polyBIMN, a functionalised conducting polymer

Conducting polymers (CPs) have wide applications in various devices such as sensors, supercapacitors, energy storage devices, dye-sensitized solar cells (DSSCs) and others. Here, detailed Time-dependent Density Func-tional Theory (TDDFT) studies on a novel functionalised conducting polymer, 2-(3-nitrophenyl)-4,7-di(thiophen-2-yl)-1H-benzo[d]imidazole) (BIMN) is reported. BIMN is a D-A-D (Donor-Acceptor-Donor) type conjugated molecule. The poly-BIMN polymer provides lower oxidation potential, lower bandgap and higher optical contrast, and is found to be useful in optical devices. The performance of various GGA, hybrid, and meta-GGA functionals to calculate the optical bandgap were studied, and the the hybrid-GGA functional PBE0 was selected to perform all calculations. All calcu-lations were performed on the ORCA 5 package. TZV basis set were used for all calculations. The 450 nm peak in the the experimental UV-Visible spectrum was resonably reproduced by the TDDFT calculations. The evolution of the bandgap for one to six rings of the oligomer was studied. Reasonable chain length saturation was obtained at 4 rings, and a bandgap of 420 nm was found for the 6-ring oligomer. Despite the calculations performed in gas phase, there results are in good agreement with the reported experimental values. It is suggested that modelling 4 rings, especially of these D-A-D molecules, is sufficient for predicting the optical bandgap.