Pump-probe and pump-deplete-probe spectroscopies on carotenoids with N=9-15 conjugated bonds

A series of all-trans-carotenoids with N=9, 13, and 15 conjugated bonds has been studied by pump-probe and pump-deplete-probe spectroscopies to obtain a systematic analysis of the energy flow between the different electronic states. The ultrafast dynamics in the carotenoids are initialized by excitation to the S-2 state and subsequently manipulated by an additional depletion pulse in the near-IR spectral range. The changes in the dynamics after depletion of the excited state population allowed differentiation of the excited state absorption into two components, a major one corresponding to the well known S-1 state and the small contribution on the red wing of the S-0-S-2 absorption band originating from the hot ground state. We found no evidence for an additional electronically excited state, usually called S-*. Instead, a deactivation mechanism that includes the hot ground state supports the observed results nicely in the framework of a simple three state model (S-2, S-1, and S-0). (c) 2006 American Institute of Physics.