Two 1,8-naphthalimide-based proton-receptor fluorescent probes for pH determination

Two newly synthesised 1,8-naphthalimide-based proton-receptor fluorescent probes N-allyl-4-(4’-N,N-diethylpropionamide-acetamido-piperazinyl)-1,8-naphthalimide I and N-(N,N-dibenzylpro- pionamide-acetamido)-4-allyl-1-piperazinyl-1,8-naphthalimide II were synthesised to monitor the change in pH in such a way that the presence of protons can increase the fluorescence intensity of these compounds. Unlike most of the other pH-sensitive probes reported, the probes possess the obvious advantage of being able to detect stronger acids at pH ≈ 2 and a combination of the two probes could detect a wider pH scale from 1.98 to 6.59; this should be very useful for monitoring the pH of the environment.