Structure dependence of electron spin polarization in Zn-porphyrin-quinoneensembles oriented in a liquid crystal

Photoinduced intramolecular electron transfer was studied by time-resolved electron paramagnetic resonance spectroscopy in two photosynthetic model sy stems oriented in a nematic liquid crystal. The donor-acceptor assemblies c onsisted of differently substituted zinc porphyrins covalently linked to a quinone with different spacers, i.e., triptycyl and cyclohexylene. The orie ntation of the guest molecules with respect to the director of the liquid c rystal was determined by line shape analysis of their triplet spectra and b y molecular modeling. It is demonstrated that the polarized pattern of the radical pair spectrum is sensitive mainly to the spacer structure, but to s ome extent also to the peripheral substituents.