The mere exposure of trans-stilbene (t-St) to three types of dehydrated medium pore acid zeolites that differ by their pore diameter induces t-St spontaneous ionization in high yield. In situ diffuse reflectance UV-visible, EPR, and Raman spectra recorded over several months highlight the exceptional stability of the charge separated states formed in ferrierite (H-FER), H-MFI, and mordenite (H-MOR). The increase in the pore diameter from H-FER to H-MOR induces different behaviors after radical cation formation. t-St*+ is stabilized for months in the narrow pores of H-FER, whereas in the larger pore H-MFI, relatively fast electron abstraction (hole transfer) takes place from the zeolite framework to create charge transfer complexes. Pulsed EPR experiments were performed using t-St and marked [D12]t-St and [13C2]t-St molecules to reveal the structural environment of the unpaired electrons through the assignment of the couplings with 1H, 2H, 13C, 27Al, and 29Si nuclei.
