Porphyrins linked to high acceptor strength cyano quinones as models for the photosynthetic reaction center

Article abstract of DOI:10.1016/0040-4020(96)00405-X

The synthesis of biomimetic photosynthetic model compounds, composed of 10,15,20-tritolylporphyrins linked to different quinones by cyclohexylene bridges, is described. Cyclic voltammetry measurements show a significant change of the reduction potential of the quinone moiety through introduction of cyano groups as electron withdrawing substituents. EPR and ENDOR spectra of the semiquinone anion radical derivatives reveal a considerable spin density redistribution within the semiquinone moiety caused by the substituents. Lamp irradiation in situ of the porphyrin hydroquinones, dissolved in reversed Triton X-100 micelles, through the resonator slits of the EPR spectrometer does not only yield hyperfine resolved absorptive, but also emissive EPR spectra. This is indicative of strong electron spin polarization effects. From the polarization pattern it can be deduced that the radical/triplet pair mechanism between two photoactive species, located in one micelle, gives rise to this effect.