Understanding the Stability of π-Conjugated Diradicaloid Organic Molecules

pi-Conjugated open-shell diradicaloid molecules have various applications in organic electronics. Herein, we have computationally designed 20 diradicaloids. The designed diradicaloids consist of a pi-bridge flanked between two carbene-derived end groups. We describe how the diradicaloid property of these molecules can be tuned through the choice of carbene end groups and pi-bridge. We quantified the diradical character of newly designed molecules using diradical indices (Y-0) and (Y-1), the fractional occupation number weighted electron density (N-FOD), and singlet-triplet energy gaps (delta E-ST). The performance of a wide range of density functional theory (DFT)-based methods is validated using complete active space self-consistent field (CASSCF) results. Global hybrid functional BHandHLYP provides the best accuracy among all DFT methods. Our results indicate that several diradicaloids are promising materials for organic electronics.