LAUSR

To evaluate the sensing ability of poly(3,4-ethylenedioxythiophene) (PEDOT) towards CO2 and SO2 gaseous molecules, an extensive quantum mechanical study has been carried out by using two different level of theories, i.e., B3LYP/6-31+G(d) and M06-2X/6-31+G(d,p). The comprehensive details of both physisorption and chemisorption mechanisms have been explored to understand the selectivity and sensitivity of PEDOT for these two analytes. Through the physisorption channel, the interaction energies of CO2 and SO2 with PEDOT are calculated as − 4.9 kcal/mol and − 7.5 kcal/mol at M06-2X/6-31+G(d,p), respectively, which indicate that the PEDOT molecule has strong sensing ability with SO2 than CO2. For the chemisorption, both [2+2] and [4+2] cycloaddition mechanisms have been explored extensively with all possibilities. The minimum activation energies have been found 38.2 and 22.7 kcal/mol for CO2 and SO2 through the [2+2] and [4+2] cycloaddition reactions with PEDOT, respectively, indicated that chemisorption mechanism is not thermodynamically favorable and kinetically accessible at room temperature. The frontier molecular orbital, natural bond orbital (NBO) charges, and UV-vis spectra analysis are further evident for the selectivity and sensitivity of PEDOT for SO2 molecule. In summary, it can be concluded that physisorption channel is more energetically favorable than chemisorption channel for PEDOT with both gases and it has greater response selectivity towards SO2 compared to CO2 at room temperature.