Molecular structure of the protonated retinal Schiff base in bacteriorhodopsin (IMAGE)
Caption
Figure 1. (a) Molecular structure of the protonated retinal Schiff base in bacteriorhodopsin (black molecular structure) and its binding pocket in the protein, consisting of amino acids and an embedded water molecule. The blue arrow indicates the electric dipole moment of retinal. (b) Molecular structure of the trans and 13-cis isomers of the protonated retinal Schiff base and schematic of the electronic potential energy surfaces of the ground state S0 and the excited states S1 and S2 along the reaction coordinate for isomerization. The mixing of the S1 and S2 states leads to the shallow potential minima in the excited states with a strong impact on the initial photoinduced dynamics. The isomerization reaction occurs upon crossing the conical intersection (CI) of the excited- and ground-state potentials. (c) Schematic of the THz Stark experiment with a strong THz pump pulse and optical probe pulse. The THz field acting on the sample is enhanced with the help of a metallic antenna structure (yellow structure on top of the grey sample layer) and reaches a value of several megavolts/cm. The THz-induced absorption change of the sample is measured with the probe pulse transmitted through the antenna gap. (d) Time-dependent electric field of the THz pulse (1 ps = 10-12 s).
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MBI/T. Elsaesser
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