The photochemical and photophysical properties of 1-azaxanthone have been studied to determine its usefulness as a probe for polarity, reactivity, and/or radical pair dynamics in supramolecular systems. Contrary to the behavior of xanthone, a structurally related ketone, the triplet-triplet absorption spectrum of 1-azaxanthone does not present polarity-induced shifts in its maximum despite its n,pi* character. Self-quenching is a remarkably fast process that occurs at nearly diffusion-controlled rates. Nevertheless, the reactivity of 1-azaxanthone toward hydrogen atom abstraction in polar media is by far superior compared to the reactivities of other aromatic ketones. This property results from the unaltered n,pi* triplet character as a consequence of the presence of a pyridine ring and makes it a convenient probe for the study of radical pair reactions and guest/host interactions in highly polar microheterogeneous systems.