Excited state structural dynamics of the charge transfer state of peridinin

We present infrared and visible transient absorption measurements of the first excited singlet state (S₁ and S_1/ICT) of peridinin in methanol, isopropanol, and chloroform solution following one-photon excitation, using 490 nm light, to excite the S₂ state that populates S₁ via rapid (∼50 fs in methanol) internal conversion. This technique enables the study of subsequent structural dynamics in S₁ involved in the formation of the charge transfer state. The S₁ lifetime of peridinin in methanol, isopropanol, and chloroform is found to be 12, 54, and 65 ps, respectively, as determined by infrared transient absorption. We observe two formation timescales in the S₁ state. We attribute the shortest timescale to relaxation following internal conversion and the longer timescale to formation of the S_1/ICT state.