Femtosecond Transient Grating Studies of Chlorophylls and Chlorophyll-Based Electon Donor-Acceptor Molecule

Article abstract of DOI:10.1021/j100021a069

Ultrafast, polarization selective, transient grating studies are performed on several chlorophylls and an electron donor-acceptor molecule, Zn DMPPH-PI, that consists of a zinc methyl 13¹-desoxopyropheophorbide a donor covalently linked to a pyromellitimide acceptor.The covalent linkage between the donor and acceptor constrains the distance and geometric relationship between them.The ability of the experiment to determine the nature of a particular physical phenomenon through separable polarization characteristics of the diffracted signal is used to analyze photophysical and photochemical processes in these molecules.This is achieved for cases in which the observed physical processes have overlapping spectral contributions, a situation where linear dichroism experiments are very difficult to interpret.Careful analysis of the absorption grating data allows us to determine rotational anisotropy values for the molecules in solution, two-photon absorption-state symmetries, and the relative orientation of the donor and acceptor in the Zn DMPPH-PI molecule.These results demonstrate complete separation of the contributions to the time dependent diffracted signal from the two radical ion pair products formed in the electron transfer reaction.