Two ground state conformers of the proton sponge 1,8-bis(dimethylamino)naphthalene revealed by fluorescence spectroscopy and ab-initio calculations

The S1 S0 transitions of the "proton sponge" 1,8-bis(dimethylamino)naphthalene have been studied by experiment and ab initio calculations. Fluorescence excitation and single vibronic level emission spectroscopy on the sample seeded in a supersonic expansion lead to the conclusion that the molecule can adopt two conformations in the ground state. This conclusion is supported by ab initio calculations at the HF/6-31G* level. The most stable conformer is shown to carry the spectroscopic characteristics of the naphthalene chromophore, while torsional motions of the dimethylamino groups dominate the spectroscopy of the other conformer.