Photophysics of 1,8-Bis(dimethylamino)naphthalene in Solution: Internal Charge Transfer with a Twist

The photophysical properties of the excited states of 1,8-(bisdimethylamino)naphthalene have been investigated by a combination of experimental spectroscopic methods and quantum chemical calculations. The experiments show that vertical excitation occurs to an 1La-type state from which internal conversion occurs to a state with dominant internal charge-transfer character. This character gives rise to weak emissive properties, a strong solvent dependence of the emission, and transient absorption spectra that carry the signature of the steady-state absorption spectra of the naphthalene radical anion. The quantum chemical calculations support the interpretation of the experimental studies, and enable us to put their results into a broader perspective. They explain the order of the lower excited states of 1,8-(bisdimethylamino)naphthalene and related compounds as well as the role of intramolecular relaxation upon excitation, thereby elucidating the large Stokes shift already observed in nonpolar solvents.