After coadsorption of electron-donor (p-terphenyl, PTP) and electron-acceptor (1,4-dicyanobenzene, DCB) molecules within the channels of silicalite-1 and MZSM-5 (M = Na + , H + ) zeolites, photoinduced or spontaneous electron transfers were investigated. In aluminum-free silicalite-1, the reaction mechanisms after PTP ionization are similar in the presence and in the absence of the acceptor molecule. Photoionization leads to a PTP •+ radical cation, which recombines directly. In NaZSM-5, p-terphenyl photoexcitation induces PTP •+ formation evolving to an electron-hole pair through capture of another electron of zeolite. This behavior is observed with and without DCB. However, when DCB is coadsorbed with PTP, recombination decays for PTP •+ and for the electron-hole pair are significantly slower. Pulsed EPR experiments show strong electron density close to DCB, through a coupling of unpaired electrons with 14 N nuclei. Nevertheless, the electron transfer remains insufficient to allow DCB •- radical anion formation. High confinement within ZSM-5 and intrinsic strength of zeolite acceptor sites might be put forward to explain the nonformation of the anion. The acceptor properties of DCB and of the zeolite might then be competitive. The zeolite electron acceptor character is even more marked when PTP is coadsorbed with DCB in acidic HZSM-5. Ionization occurs spontaneously, and transient species are stabilized for months. No electronic coupling with nitrogen atoms of DCB could be observed, indicating no partial transfer to the acceptor molecule and electron trapping in acidic zeolite.