Synthesis and spectral properties of a hydrophobic fluorescent probe: 6-propionyl-2-(dimethylamino)naphthalene.

Environmentally sensitive fluorescent probes involve two groups, an electron donor and an electron acceptor, attached to an aromatic ring system, and maximal effects may be expected when these groups are as far apart as feasible. The syntheisis, characterization, and spectroscopic properties of 6-propionyl-2-(dimethylamino)naphthalene (PRODAN), a compound that fulfills these conditions, are described. The maximum of emission is at 401 nm in cyclohexane solution and at 531 nm in water solution, indicating an increase of dipole moment of approximately 20 D units on excitation to the lowest singlet state. The effect of temperature upon the spectral distribution and the bandwidth of fluorescence of PRODAN in 1:1 complexes with albumin shows the existence of a dynamic relaxation process of the protein surroundings within th 2-4 ns of the fluorescence lifetime.