Methylviologen (MV(2+)) incorporated within medium- and large-pore zeolites (NaZSM-5, Namordenite, NaY, and CsY) emits fluorescence at 330 and 420 nm; the latter is most prominent in zeolite NaY. The intensity ratio between these two bands depends on the structure of the zeolite. On the basis of molecular modeling and C-13 CP/MAS NMR using the dipolar dephasing technique, the first band has been ascribed to the emission of MV(2+) in a planar conformation. The unprecedented 420 nm band has been attributed to a twisted conformer probably interacting with the basic oxygen sites of the framework.