The trans to cis isosomerization of the central para-coumaric acid (pCA) chromophore in photoactive yellow protein. There are Nobel prizes for theoretical simulations of these chemically extremely important isomerizations. We observe it, for the first time ever, directly by shifting electron density clouds, and on the fly!!!, ultrafast, in extreme slow motion (Pande et al., 2016, Science 352, 202-206), see also: Recent Highlights.

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