Two-path photo-induced electron transfer in naphthalimide-based model compound

A photo-induced electron transfer (PET) model compound in the form acceptor–fluorophore–donor and its reference compounds were synthesized. Because the fluorescence of the fluorophore 4-amino-1,8-naphthalimide (ANI) was quenched by any PET process from donor to fluorophore (PET input path) or from fluorophore to acceptor (PET output path), therefore, if one of the above two paths was switched off, the occurrence of the PET process via the other PET path could be investigated by the fluorescence behavior of 4-amino-1,8-naphthalimide. Thus, the two-path PET in the model compound could be probed individually through the fluorescence signal of 4-amino-1,8-naphthalimide. Switching off the PET input path could be achieved by protonation (or quaternization) of the tertiary amine donor. The intramolecular electric field, which forced the electron transfer to proceed via the output path, could be destroyed through symmetrization of the model compound by the introduction of an identical amine substituent on the non-substituted 1,8-naphthalimide acceptor. It is worth noting that once either of the paths was of the status of "on", PET occurred and the fluorescence signal of 4-amino-1,8-naphthalimide was quenched.