We report on our method to perform fifth-order 3D electronic spectroscopy (3DES) based on a pulse-shaper assisted pump-probe beam geometry setup. Fifth order 3D spectra, involving three coherence periods and two separate controllable population/waiting time periods can be obtained. We show how 8-step and 27-step phase cycling schemes can measure purely absorptive 3D spectra as well as 3D spectra for the individual fifth-order processes that contribute to the purely absorptive spectrum. With appropriate phase cycling schemes, the exact same setup can be switched from performing 2D to 3D optical spctroscopy.We apply this technique to the study of the excitonic energy transfer (EET) processes of LHC II light harvesting. The EET process in light harvesting complexes is typically complex and proceeds in a multistep fashion. Third order two dimensional spectroscopy (2DES) has been used to study the EET processes in several light harvesting complexes. In 2DES, the spectra are presented in two frequency dimensions: one excitation frequency and one of the emission frequency. The crosspeaks on the 2D spectra correlates the donor exciton to the acceptor exciton. As this is a two point correlation, multistep processes can only be indirectly observed. In 3DES, with an additional frequency axis, three-step processes can be directly observed. A crosspeak on a 3D spectrum at (?a , ?b , ?c) will denote exciton a transferring energy to exciton c, via an intermediate exciton b. We have performed 3DES on LHCII trimers, and directly observed for the first time multistep EET process.

Fifth order 3D electronic spectroscopy of light harvesting complexes

248th National Meeting (2014)

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