Subpicosecond infrared spectroscopy on the photoisomerisation of the protonated Schiff base of all-trans retinal

The light induced isomerisation reaction of the protonated Schiff base retinal with butylamine was studied in solution by subpicosecond infrared spectroscopy in the spectral range of the CC, CC and CNH+ stretching modes. Upon heating by the internal S1 → S0 conversion process, vibrationally hot molecules are formed which are characterized by pronounced red-shifts of the CC, the CC and CNH+ stretching modes. The frequency shifts can be used to estimate an intramolecular temperature of the chromophore of 550 K immediately after the S1 → S0 transition.