Calculation of conductive polymer-based SO₂ and SO₃ gas sensor mechanisms by using the DFT method

In this study, we carried out with the DTP (dithieno(3,2-b:2,3-d) pyrrole) molecule which is a member of the conductive polymer class that is one of the topics that have been studied prevalently in recent times, and the density functional theory's (DFT) calculation methods were used to shed light on the sensor mechanisms of its interactions with SOx (SO₂ and SO₃) sulfur oxides. The changes in the geometric and electronic characteristics of a sensor mechanism designed with the DTP molecule when it encountered sulfur oxides were examined. With these changes, the usability of DTP as a sensor material was proven. DTP sensor applications using this method were not investigated in previous studies. The B3LYP 6-31 G(d) levels of DFT were used in the calculations. In the calculations, during the interaction between analyte (SO₂-SO₃) and the conductive polymer DTP (dithieno(3,2-b:2,3-d) pyrrole), especially, the changes in its geometric and electronic structures were observed. With these changes that were observed in the geometric structure, as a result of the interaction between the conductive polymer and gas molecules, the resistance on the polymer's main chain decreased, and conductivity increased. Calculations on the bandgap on HOMO-LUMO energy levels were observed to decrease. Thus, the structural conductivity of the molecule increased. Additionally, the experiments showed that, as a result of interaction with gas molecules, the bandgap in the ionization potential, electron affinity, and HOMO-LUMO energy levels varied. These variations showed the detection mechanisms for sulfur oxides by the DTP (dithieno(3,2-b:2,3-d) pyrrole) molecule that may be used to design sensors.