The aim of the present work was to find a ketoprofen (KP) equivalent suitable for time-resolved studies on the interactions of its KP-like triplet state with biomolecules or their simple building blocks, under physiologically relevant conditions. Such a compound should fulfill the following requirements: (i) it should be soluble in aqueous media; (ii) its triplet lifetime should be longer than that of KP, ideally in the microsecond range; and (iii) its photodecarboxylation should be slow enough to avoid interference in the time-resolved studies associated with formation of photoproducts. Here, the glycine derivative of ketoprofen (KPGly) has been found to fulfill all the above requirements. In a first stage, the attention has been focused on the photophysical and photochemical properties of KPGly, and then on its excited-state interactions with key amino acids and nucleosides. In acetonitrile, the typical benzophenone-like triplet-triplet absorption ((3)KPGly) with lambda(max) at 520 nm and a lifetime of 5.3 mu s was observed. This value is very close to that of (KP)-K-3 (5.6 mu s) obtained under the same conditions. In methanol, the (3)KPGly features were also close to those of (KP)-K-3 with detection of a short-lived triplet state that evolves to give a ketyl radical. By contrast with the behavior of KP, in deaerated aqueous solutions at pH = 7.4, the transient detected in the case of KPGly displayed two bands at lambda(max) at 330 and 520 nm, very similar to those observed in acetonitrile solution but with a lifetime of 7.5 mu s at 520 nm. Hence, it was assigned to the KPGly triplet. In the case of KP, efficient decarboxylation occurs in the subnanosecond time scale, via intramolecular electron transfer. This process gives rise to a detectable carbanion intermediate (lifetime similar to 250 ns) and prevents detection of the shorter-lived (KP)-K-3 signal. In a second stage, the attention has been focused on the excited-state interactions between (3)KPGly and amino acids or nucleosides; for this purpose, 2'-deoxyguanosine (dGuo), thymidine (Thd), tryptophan (Trp), and tyrosine (Tyr) have been chosen as photosensitization targets. In general, efficient quenching (rate constant k(q) > 10(9) M-1 x s(-1)) was observed; it was attributed for dGuo, Tyr, and Trp to a photochemical reaction involving initial electron transfer from the biological target to (3)KPGly, followed by proton transfer from the amino acid or the nucleoside radical cation to KPGly(-center dot). As a matter of fact, ketyl radical together with guanosinyl, tyrosinyl, or tryptophanyl radicals were detected; this supports the proposed mechanism. The results with Thd were somewhat different, as the efficient (3)KPGly quenching was ascribed to oxetane formation by a Paterno BUchi photocycloaddition.