If you have a molecule such as a quinoline or an indole, if it is treated with an acidic solution, does fluorescence get enhanced because the n-Pi* state is no longer possible or because photoinduced electron transfer from the donor nitrogen to the Pi* state of the quinoline moiety is no longer possible (in the way molecular sensors work)?

I understand that photoinduced electron transfer involves molecules with donor and acceptor moieties with a spacer in between but I am also aware that PET can occur in molecules where the donor and acceptor moieties are integrated such as in quinolines and indoles.