The full AM1 optimized geometries and energies of some para-substituted N,N-dimethylaniline derivatives in their ground and first singlet excited states have been used to probe if either a rotational isomerization or a change in the nitrogen pyramidalization could explain the dual fluorescence phenomenon. The internal charge transfer state characteristics are given from the AM1 theoretical study of the free molecules. Solvent effects have been analyzed using a microstructural solvation model associated with the AM1 results. This theoretical study infers that the dual fluorescence phenomena can be related to the presence of a twisted internal charge transfer state which is stabilized even in a nonpolar solvent but cannot be related to the presence of a wagged internal charge transfer state, even in a strong polar solvent.