Laser spectroscopy of a chiral drug in a supersonic beam: conformation and complexation of S-(+)-Naproxen

The S0–S1 electronic transition of jet-cooled Naproxen has been investigated by laser-induced fluorescence excitation and emission spectroscopy. Two electronic transitions separated by 102 cm−1 have been evidenced and attributed to the presence of two conformers. With the help of DFT calculations, the structure of these conformers has been shown to correspond to a rotation by 180° of the chiral substituent with respect to the aromatic plane. When associated with alcohols, both conformers of the chromophore form complexes which give rise to different microscopic solvent shifts of the S0–S1 transition. In the case of complexation with R- or S-2-butanol, the hetero- and homo-chiral pairs are characterised by different spectroscopic patterns, which allow a clear discrimination between them.