Time-resolved fluorescence study of all-trans-retinal

UV-vis steady-state and time-resolved emission techniques were employed to study the ultrafast relaxation path of all-trans-retinal. We found that the steady-state emission spectrum consists mainly of two bands that we assign to the allowed transition from the state and the forbidden transition from the (ππ) state. The time-resolved emission signal is dependent on the excitation wavelength, and is composed of three decay components. The short-time component of less than 80 fs, irrespective of the solvent, is assigned to the transition from the state. The intermediate-time decay component is assigned to the transition from the (ππ) state, depends on the solvents polarity and not on the existence of hydrogen bonds between the solute and the solvent or the viscosity of the latter. It has a lifetime of ~1 ps in polar solvents, and of 0.6 and 0.4 ps in the non-polar solvents n-octane and cyclohexane, respectively.