DUAL FLUORESCENCE OF 4-N,N-DIMETHYLAMINOPYRIDINE - ROLE OF HYDROGEN-BONDED COMPLEX IN THE GROUND-STATE

A correlation is shown between the appearance of the dual fluorescence of 4-N,N-dimethylaminopyridine (DMAP) solutions and the formation of hydrogen-bonded complexes in the ground state. A comparative absorptio n study between pyridine, N,N-dimethylaniline and DMAP shows that the hydrogen-bonded complex is situated on the amino nitrogen of DMAP. A ' 'pretwisted'' conformation of DMAP in the ground state is assumed due to this hydrogen-bonded complex. Simulations by intermolecular interac tion calculations and spectroscopic calculations (CNDO/s) confirm the ''twisting'' influence of water molecules (and/or any other hydrogen b onding) on the amine in the ground state. This ''pretwisting'' in the ground state by hydrogen bonding is common in many other aromatic amin es. Moreover, the deforming role of hydrogen bonding in the ground sta te seems to be a general phenomenon in flexible aromatic molecules.