Synthesis and Geometry Determination of Cofacial Diporphyrins. EPR Spectroscopy of Dicopper Diporphyrins in Frozen Solutions

Article abstract of DOI:10.1021/ja00297a024

Frozen solution EPR spectra have been obtained for the dicopper complexes of six covalently linked diporphyrins whose synthesis is also described.The distance between the copper atoms in the diporphyrins was determined from the ratio of the intensity of the half-field transitions to the intensity of the allowed transitions and by computer simulation of the spectra.The values obtained by the two methods were in good agreement and ranged from 4.1 to 5.6 Angstroem.The porphyrin planes were parallel within experimental uncertainty.The angle between the interspin vector and the normal to the porphyrin planes (slip angle) was determined by computer simulation of the spectra and values ranged from 20 degree to 45 degree.For the majority of the diporphyrins the separation between the porphyrin planes was 3.9 +/- 0.1 Angstroem.In an anthracene pillared diporphyrin the interplanar separation was 4.6 Angstroem.These results were compared with those determined from crystal structures.Although there was no short bond pathway between the two copper atoms, the simulations of the spectra indicated that the absolute value of the copper-copper exchange interaction, J, was >0.3 cm^-1.