Excited-State Sudden Polarization Dynamics of Sulfone-Functionalized Symmetric Stable Diradicaloids

The sudden polarization (SP) effect converts a resonant zwitterionic state into a polarized charge-separated (CS) state, yet its dynamics in stable diradicaloids remain insufficiently understood. Here we investigate a pair of C₂-symmetric sulfone-functionalized Chichibabin's hydrocarbons with nearly degenerate zwitterionic states but differing in symmetric electron-withdrawing groups (EWGs). Femtosecond transient absorption spectroscopy directly captures subpicosecond SP processes in both systems and, together with quantum-chemical calculations, reveals the thermodynamic accessibility of the CS state governed by solvent polarity and excitonic coupling. Increasing solvent polarity facilitates the SP effect, which leads to full charge separation via the relaxation of polarized zwitterionic states. Additionally, weakening excitonic coupling through the substituent effect allows the CS state to be accessible across all polar media. These results establish the SP effect as the trigger for symmetry breaking and establish tunable substituents and dielectric environments as effective handles for directing SP relaxation dynamics in symmetric diradicaloids.