Conical intersection dynamics in Rhodopsin and its analog isorhodopsin

In this paper, pump-probe spectroscopy with simultaneous sub-20-fs time resolution and broad spectral coverage from the visible to the near infrared was used to track the wavepacket motion through a conical intersection (CI) in rhodopsin (Rh). Results show that the wavepacket reaches the CI in ≈75 fs, after which it leaves the excited state of the reactant. The transient signals were simulated by hybrid quantum-mechanical/molecular-mechanical trajectories following the evolution of the opsin-embedded chromophore from the excited to the ground electronic state. Excellent agreement between the experimental observations and molecular dynamics calculations that involve a true electronic state crossing were observed. This suggests that the CI seam has a strongly “peaked” topography.