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Conical Intersections of Retinal

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Since Newton, vision has attracted physicists seeking to explain how light is sensed by organisms. Recently, the structure of a visual receptor protein has been solved crystallographically and physicists have a new opportunity to explain vision in atomic level detail. Vision starts with optical excitation of retinal, located in the receptor protein, and the subsequent vibrational - torsional motion in retinal's electronically excited state. Retinal reaches within less than a picosecond (0.000000000001 s) geometries for which excited state and ground state merge energetically, the so-called conical intersections. Here retinal converts back to the ground state and becomes trapped into a new stable geometry. A recent study by the Theoretical Biophysics Group explains how the conical intersections of retinal steer retinal towards the right trapped geometry, one that is capable of triggering a visual signal.