PHOTOCHEMISTRY AND PHOTOPHYSICS OF 1-AZAXANTHONE IN ORGANIC-SOLVENTS

The photochemical and photophysical properties of 1-azaxanthone have b een studied to determine its usefulness as a probe for polarity, react ivity, and/or radical pair dynamics in supramolecular systems. Contrar y to the behavior of xanthone, a structurally related ketone, the trip let-triplet absorption spectrum of 1-azaxanthone does not present pola rity-induced shifts in its maximum despite its n,pi character. Self-q uenching 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 f rom the unaltered n,pi triplet character as a consequence of the pres ence 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.