Proton transfer of magnolol in ground and excited states

Magnolol, 5′,5-di-2-propenyl-[1,1′-biphenyl]-2,2′-diol, has been characterized by steady-state and time-resolved spectroscopy as well as 1H MR and 13C NMR. And the proton transfer reactions both in ground and excited states have been investigated. The binary acid enhances its acidity upon excitation at the first deprotonation reaction and exhibits strong photoacidity. The relationship between the spectroscopic property and the geometric conformation of magnolol with unique biphenyl group has been discussed.