Effects of Spatial Constraints and Brønsted Acid Site Locations on para‐Terphenyl Ionization and Charge Transfer in Zeolites

The locations of Brønsted acid sites (BAS) in the channels of medium‐pore zeolites have a significant effect on the spontaneous ionization of para‐terphenyl (PP₃) insofar as spatial constraints determine the stability of transition states and charge‐transfer complexes relevant to charge separation. The ionization rates and ionization yield values demonstrate that a strong synergy exists between the H⁺ polarization energy and spatial constraints imposed by the channel topology. Spectroscopic and modeling results show that PP₃ incorporation, charge separation, charge transfer and charge recombination differ dramatically among zeolites with respect to channel structure (H‐FER, H‐MFI, H‐MOR) and BAS density in the channel. Compartmentalization of ejected electrons away from the initial site of ionization decreases dramatically the propensity for charge recombination. The main mode of PP₃^.+ decay is hole transfer to form AlO₄H^.+ ??? PP₃ charge‐transfer complexes characterized by intense absorption in the visible range. According to the nonadiabatic electron‐transfer theory, the small reorganization energy in constrained channels explains the slow hole‐transfer rate.