[Nescafe]

Hi,

I keep on reading that "pH sensitivity is due to a reconfiguration of the fluorophore's π-electron system that occurs upon protonation". But what happens exactly? I have learnt that in the protonated form they are less fluorescent. So the fluorescence is decreasing as the electron density within the fluorophore itself is reduced, but I cant wrap my head around what is the fundamental reason behind this? I can kind of imagine that as you lose electrons the likelyhood of exciting electrons to a higher energy state and therefore energy emission (light) decreases but is there another reason as to why the fluorescence decreases?

Thanks =)

Nescafe.