Fig. 3

(a) (i) Mechanistic possibility involving an alkene as a directing group for Au(III) to activate a carbonyl group towards hydrolysis. (ii) Model substrate with a thiol directing group failed to release free amine, eliminating the possibility of such a mechanism. (b) Phenyl amide with its lone pair in conjugation with the ring did not show any reaction, while the benzyl amide results in complete release of the free amine, suggesting that the carbonyl group should initially act as a nucleophile through its C–O resonance form. (c) Naphthalimide-based fluorogenic probes (QF1–4) were designed to study the cleavage efficiency of the Au(III) for uncaging alkene-containing molecules. The caged naphthalimide derivatives exhibited high stability in solution, and their quenched fluorescence could be reactivated upon removal of the caging group (λex = 445 nm, λem = 535 nm). (d) Representative example with QF4 demonstrating the increase in fluorescence intensity during the time course of the uncaging reaction with Na[AuCl4]. (e) Determined half-time for the uncaging reaction for QF1–4. QF3 showed no increase of fluorescence under standard reaction conditions. (f) HPLC trace showing the formation of F4 from QF4 upon treatment with Na[AuCl4] at 37 °C. Time = 0 h is the time point recorded prior to the addition of the Au salt.