Resolving the primary dynamics of bacteriorhodopsin, and of a `C13C14 lockedʹ analog, in the reactive excited state

The evolution of stimulated emission from the reactive excited state of bacteriorhodopsin is compared with that of a modified protein containing a synthetic retinal which is unable to twist around the C13C14 bond. The rise of the emission is demonstrated to be structured, multistaged and wavelength dependent, appearing later in the red edge of the emission bands in both proteins. Spectral modulations associated with vibronic wavepacket motion are also observed in both. The mechanism of strong Stokes shifting of the emission resolved here, and the nature of coherences observed in the excited state are discussed.