Abstract
The nondegenerate two-photon absorption spectrum of all- trans retinal in a nonpolar solvent at room temperature has been measured for the first time. The multichannel detection utilizing the technique of femtosecond time-resolved pump–probe absorption spectroscopy has enabled us to obtain precise two-photon absorption spectra. It was found that the two-photon absorption maximum of all- trans retinal is located at 376 nm, which is 7 nm longer than the one-photon absorption peak. This peak wavelength difference indicates the 500-cm −1 energy gap between the S 3 (B u) state and the S 2 (A g) state. On the basis of the obtained two-photon absorption data and the available fluorescence data, we determined the 0–0 position of the S 2 state to be 2.47 × 10 4 cm −1.
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