Transient absorption from the 1Bu+ state of all-trans-beta-carotene newly identified in the near-infrared region.

We have attempted subpicosecond time-resolved absorption spectroscopy of all-trans-beta-carotene in organic solvents in the 820-1060 nm region and found novel transient absorption features which lived in subpicosecond time scales. A first component that appeared immediately after excitation showed a lifetime of 190 +/- 10 fs in n-hexane in agreement with the 1Bu+ lifetime that had been determined by fluorescence upconversion spectroscopy (195 +/- 10 fs). (Kandori et al. [1994] J. Am. Chem. Soc. 116, 2671-2672.) Therefore, this component is assigned to a transient absorption from the 1Bu+ state.