1,5-Prodan Emits from a Planar Intramolecular Charge-Transfer Excited State.

1-Propionyl-5-dimethylaminonaphthalene (, 1,5-Prodan) and two derivatives where the amino group is constrained in a seven-membered () and five-membered () ring are prepared. All three exhibit strong fluorescence and similar degrees of solvatochromism. Their fluorescence is strongly quenched in alcohol solvents. Because the amino group in and especially is forced to be coplanar with the naphthalene ring, the similar photophysical behavior of all three suggests that emission arises from a planar excited state (planar intramolecular charge transfer).