Figure 5.

Trans-to-cis isomerization in PYP. Weighted difference electron-density maps are shown in red (−3σ) and blue (3σ). The reference structure is shown in yellow, structures before the transition (but still in the electronic excited state) are shown in pink and the structure after transition in the ground state is shown in green. Important negative features are denoted α and positive features are denoted β. Pronounced changes are highlighted with arrows. (a, b, c) Representative time delay before transition. Dashed line: direction of the C2=C3 double bond, feature β1. Dotted lines: hydrogen bonds of the ring hydroxyl to Glu46 and Tyr42. Chromophore configuration from 100 to 400 fs pump–probe delay. (d) Chromophore configuration at 799 fs after transition. (e, f) Chromophore configuration at longer times from 800–1200 fs. (g) 3 ps chromophore configuration; the dashed line shows the direction of β (Pande et al., 2016 ▸).