Halogen-Dependent Switching between σ-Hole and π-Hole Donor Modes in Bifunctional Halopolyfluorobiphenyl Platforms: From Perfluoroarene–Arene Stacking to Dominant Halogen Bonding

This study systematically investigates the halogen-dependent interplay between σ-hole (halogen bonding) and π-hole (perfluoroarene–arene stacking) interactions using a bifunctional perfluoroarene–arene XPh F Ph (X = F, Cl, Br, I) molecular scaffold. In all cases, molecular self-organization gives rise to infinite chains driven by Ar F –Ar interactions. Through cocrystallization with nitrogen Lewis bases DABCO and 4,4’-azopyridine, we reveal a remarkable gradient-controlled binding selectivity. Our results demonstrate a clear switching mechanism: a weaker halogen donor (Cl) preferentially engages in Ar F –Ar interactions, whereas stronger halogen donors dominate through halogen bonding, suppressing Ar F –Ar association. The experimental findings are corroborated by a comprehensive computational study using molecular electrostatic potential mapping, QTAIM, and EDA. Our calculations quantify the competitive energetic landscape, revealing that while perfluoroarene–arene stacking remains energetically stable across the series, the surge in σ-hole positivity reaching a maximum for IPh F Ph drives the transition toward dominant halogen bonding with Lewis bases.