DETERMINATION OF THE ELECTRON-TRANSFER PARAMETERS OF A COVALENTLY-LINKED PORPHYRIN-QUINONE WITH MESOGENIC SUBSTITUENTS - OPTICAL SPECTROSCOPIC STUDIES IN SOLUTION

The photoinduced electron transfer (PET) of a covalently linked porphy rin-quinone with mesogenic substituents was studied using visible and near-IR (NIR) spectroscopy. Mesogenic substituents were introduced at the porphyrin moiety in order to mimic the anisotropic membrane proper ties of the native reaction centre of photosynthesis. Photophysical ch aracterization of this system in homogeneous solution is a prerequisit e for a better understanding of the effects occurring in anisotropic m edium. For this reason, we studied the fluorescence and phosphorescenc e quenching and lifetime of the charge-separated state. Time-resolved fluorescence measurements indicated an effective singlet PET, The comp lete set of PET parameters was calculated using Marcus theory of non-a diabatic electron transfer (ET). Steady state measurement of singlet o xygen luminescence, which allows indirect access to phosphorescence qu enching, indicated that no tripler PET was involved in the decay proce sses. Using transient absorption spectroscopy, the lifetime of the cha rge-separated state was found to be 1.9 ns. (C) 1997 Elsevier Science S.A.