Carotenoid response to retinal excitation and photoisomerization dynamics in xanthorhodopsin

► Ultrafast spectroscopy of xanthorhodopsin (XR) and bacteriorhodopsin (BR). ► Salinixanthin (SX) in XR exhibits an electrochromic shift after retinal excitation. ► Electrochromic shift of SX decays co-ordinately with excited state of retinal. ► Differences in ultrafast dynamics of XR and BR were found.