Ionization of chlorophyll-c2 in liquid methanol

The ionization of chlorophyll-c2 in liquid methanol was investigated by a sequential quantum mechanical/Monte Carlo approach. Focus was placed on the determination of the first ionization energy of chlorophyll-c2. The results show that the first vertical ionization energy (IE) is red-shifted by 0.47 ± 0.24 eV relative to the gas-phase value. The red-shift of the chlorophyll-c2 IE in the liquid phase can be explained by Mg⋯OH hydrogen bonding and long-ranged electrostatic interactions in solution. The ionization threshold for chlorophyll-c2 in liquid methanol is close to 6 eV.