Unveiling the Spectroscopic\nSignatures of Poly(3,4-ethylenedioxythiophene)\nby Controlling Polaron and Bipolaron Concentrations

The electronic and\noptical properties of conductive polymers\n(CPs)\nare related to the formation of polarons and bipolarons localized\nalong the polymer backbone. Their concentration is affected by the\nconformational and morphological features of the CPs, making it crucial\nto understand how they are affected by chain conformation and π-electron\ndelocalization. In this work, we studied the modulation of the concentration\nof polarons and bipolarons in PEDOT:PSS after post-treatment with\nhydrazine and H<sub>2</sub>SO<sub>4</sub>, which influence the optical\nand electronic properties. Through a combination of electron spin\nresonance spectroscopy, UV–vis–NIR spectroscopy, Raman\nspectroscopy, and conductivity measurements, we evaluate changes in\nthe properties of PEDOT, which are related to the chain conformation\nand π-electron delocalization within the polymer backbone. We\npresent experimental evidence supporting the recently revised interpretation\nof the UV–vis–NIR spectrum of PEDOT:PSS, and through\na combination of theoretical and experimental analysis, we propose\na new interpretation of the Raman spectrum of PEDOT:PSS. Furthermore,\nwe provide the first experimental evidence of the presence of polaron\npairs in the triplet state in PEDOT:PSS, which have a spin of S =\n1, which were only predicted theoretically up to this point.