Spectroscopic and theoretical studies of the excited states of fenofibric acid and ketoprofen in relation with their photosensitizing properties

A study of the different excited states of fenofibric acid (FB) and ketoprofen (KP), two aromatic acids derived from benzophenone, has been achieved by absorbance and low temperature emission spectroscopy to take into account their photochemical reactivity and their in vitro and in vivo photosensitizing properties. These experiments have shown that FB mainly exhibits a singlet-singlet transition of pi pi* character, the n pi* transition being undetectable, in contrast with KP. In phosphate buffer as well as in ethanol or in isopentane, the lowest triplet excited state of fenofibric acid appears to be, as for KP, an n pi* triplet state with characteristics similar to those of benzophenone. These assignments were fairly well supported by theoretical calculations performed at the TD-DFT level. The transient formation of a ketyl radical detected in hash photolysis experiments performed in ethanol confirms that the photochemical reactivity of FB towards hydrogen abstraction in ethanol is typically that of an n pi* triplet state. The good agreement between the experimental and theoretical results is discussed with respect to those previously obtained by ether theoretical methods.