Polaron Induced Conductance Switching in Conjugated Oligophenylene: A First-Principles Analysis

For π-conjugated systems, polaron formation has a major impact on their optoelectronic properties. In fact, for such systems, an exquisite interplay between electron delocalization and the steric effect determines their ground state properties. However, an excess charge (positive or negative) injection causes structural reorientation because of extended conjugation. Herein, we investigate the effect of such an excess charge in an individual polyphenylene on its quantum conductance behavior. By combining the DFT and NEGF formalisms, we characterize both structural and electronic changes occurring upon electron and hole injection. We demonstrate that for both the cationic and anionic radicals, the excess charge is observed to be localized, inducing a partial planarization of the molecule and forming cationic and anionic polarons, respectively. The calculated low-bias conductance values determine the polaronic effect and could be implemented for easy determination and measurement of polaron formation. In fact, cationic and anionic polarons induce a large degree of conductance switching, involving a decrease and increase of conductance, respectively.