Photophysical studies on molecular chirality: Ground and excited state enantioselective interactions between 2-naphthyl-1-ethanol and natural bicyclic compounds

Jet-cooled isolated diastereoisomeric pairs formed between R- and S-2-naphthyl-1-ethanol and a series of optically active terpenes have been investigated by studying both the fluorescence excitation spectra and the fluorescence decays. While the homo- and heterochiral complexes with cr-pinene and borneol can be resolved spectrally, no spectral enantiodifferentiation was obtained in the case of camphene and camphor complexes. Chirality-dependent fluorescence decays were however observed for these complexes which exhibit either longer lifetimes than the bare chromophore for the diasteroisomers involving camphene, or shorter for those with camphor. The enantioselective quenching of fluorescence of 2-naphthylethanol by R- and S-camphor has also been observed in n-hexane solution and has been shown to be due to a singlet-singlet energy transfer taking place at a rate lower than diffusion. In contrast, the energy transfer to R- and S-camphorquinone and biacetyl was shown to be diffusion controlled and nonenantioselective.